EFFECT OF INTERCROPPING AND TILLAGEIRESIDUE MANAGEMENT
ON PLANT COMPETITION FOR WATER AND NUTRIENTS
by
SALlBO SOME
8.S., University of Ouagadougou, Burkina Faso, 1982
M.S., University of Georgia, 1985
A Dissertation Submitted to the Graduate Faculty of the
University of Georgia
in partial Fulfillment of the Requirements
for the Degree
DOCTOR OF PHILOSOPHY
ATHENS, GEORGIA
1993

RESUME
TRADUIT
DE
L A
THESE
EFFETS DE L'ASSOCIATION DES CULTURES
ET DU TRAVAIL DU SOL/GESTION
DES RESIDUS SUR LA COMPETITION DES PLANTES POUR
L'EAU ET LES ELEMENTS NUTRITIFS.
Problematique-Materiels et Methodes
Dans l'agriculture traditionnelle en Afrique de l'Ouest, les paysans ont
toujours pratique 1 'association des cultures sous divers systemes de gestion des
residus
de
recol te,
engendrant une
grande variabili te dans
les
rendements.
Malgre les difficultes enormes inherentes aces systemes complexes de production,
on y constate un deficit d'attention de la part des chercheurs.
Nos travaux
avaient pour but d'etudier, d'une part, les effets de 1 'association des cultures
sur la competition entre les plantes pour l'eau et les elements mineraux,
et
d'autre part, les effets des differentes pratiques de travail du sol/gestion des
residus de recolte sur les cultures et la fertilite chimique et physique du sol,
et enfin, d'etudier les interactions existant entre pratiques que de travail du
sol/gestion des residus et systemes d'association des cultures.
Pour cela nous avons utilise un dispositif "split-plot" pour, d'une part,
comparer la pratique paysanne courante qui consiste a exporter les residus de
recolte en fin de campagne, puis a semer directement au debut de la campagne
suivante avec les pratiques de 1 'incorporation des residus de recolte par labour
conventionnel (pratique courante dans les exploitations modernes industrielles)
et de semi direct sur sol paille (pratique conservatoire anti-erosive recommandee
par
certains
auteurs),
et
d' autre
part,
comparer
les
associations de
deux
legumineuses,
l'arachide,
Arachis
hypogeae
L.
et
le
mucuna,
Stizolobium
deeringianum (une legumineuse en regain d'interet comme engrais vert et four rage
dans les Ameriques du nord et du sud.) avec le sorgho, sorghum bicolor Moher.
Ces
etudes
ont
ete
menees
en Georgie
aux U. S .A.
dans des
conditions
pedologiques et agroclimatiques se rapprochant de celles du Burkina Faso dans le
but de favoriser la transferabilite des resultats.
Les resultats se presentent
succinctement comme suit:
Comparaison des Pratiques du Travail du Sol/Gestion des Residus
1) L'exportation des residus de recolte appauvrit plus rapidement le sol
en elements mineraux disponibles et surtout en azote total, contrairement a leur
incorporation ou a leur maintien a la surface du sol
(paillage),
ces deux
dernieres pratiques favorisant un recyclage des elements mineraux dans le sol.
2) Les sols nus emblaves directement presentent un avantage d'humidite par
rapport aux sols ayant fait 1 'objet d'incorporation des residus de recolte par
labour conventionnel.
3) Les mesures de l'infiltration de
l'eau par simulation de pluie ont
montre une meilleure
infiltration de
1 'eau dans
les
parcelles
nues
a
semis
directs par rapport a celle dans les sols laboures, expliquant les differences
observees en humidite du sol.
Nous avons
explique
cette difference par
la
presence possible d'une macro-porosite cree apres la decomposition des vieilles
racines
dans
les
parcel1e a
semis direct d 'une part,
et d I autre
part,
par
l'encroutement superficiel favorise par le labour fin qui reduit la penetration
de 1 'eau dans les parcelles labourees.
Le paillage est connu pour reduire 1es
risques d'encroutement superficie1 du sol, le ruissellement et 1 'evaporation de
l'eau,
ainsi que pour
favoriser la creation de
la macro-porosite du sol
par
1 'action des invertebres telluriques.
Cela exp1ique certainement 1 'infiltration
significativement e1evee dans les sols pailles a semi direct comparativement aux
deux
trai tements
precedents,
justifiant
du
meme
coup
leur
superiori te
en
humidite.

Ces observations suggeres que si labour grossier une strategie de collecte
et de conservation des eaux dans les
regions a pluviometrie incertaines telle
qu'au Burkina Faso, le labour fin doit y etre par contre deconseille.
4) Eu egard aux differences observees pour l'humidite et la fertilite des
sols des differents traitements,
le developpement racinaire des cultures etait
plus eleve dans les parcelles paillees que dans les parcelles nues ~ semi direct
ainsi que dans celles conventionnellement labourees.
5) Par consequent, la production globale de biomasse etait plus importante
dans
les
parcelles
~
semi
direct
paillee
que
dans
celles
labourees
conventionnellement et 1992 OU la pluviometrie etait deficiente.
La teneur en
azote et en potassium etait plus elevee dans les parcelles ~ semi direct paillees
que dans les deux autres trai tements principaux ~ la fin de I' experience en 1992.
Comparaison des Traitements de Cultures
6) Le rendement du mucuna en biomasse aer1enne, en azote (N) et en calcium
(Ca) etait plus eleve que celui des deux autres cultures en 1991 comme en 1992.
Son rendement en biomasse etait en moyenne de 11 393 kg/ha en 1991 et 9 544 kg/ha
en 1992 pendant que celui en N avoisinait 200 kg/ha quelque soit le systeme de
labour/gestion des residus de recolte, particulierement en 1992.
Cependant, les
sols ~ mucuna sont restes comparables aux autres sols quant ~ la teneur en N et
en Ca, probablement parce que la duree de l'experience etait insuffisante pour
permettre un recyclage de la totalite des residus produits.
Seul la teneur en
potassium (K) etait plus elevee dans les sols ~ mucuna dans les premiers 7,5 cm
de profondeur apres les deux annees de 1 'experience.
7)
En depi t
de
leur
bonne
couverture
par
la
biomasse
au
cours
de
la
campagne,
les sols ~ mucuna presentaient une humidite < sols ~ sorgho < sols a
arachide.
Mais la densite racinaire chez le sorgho etait > mucuna > arachide.
Cela suggere que meme si la densite racinaire est important pour un prelevement
maximum de l'eau du sol elle n'est pas le seul facteur d'epuisement.
8)
La
teneur
en
eau
reduite
dans
les
parcelles
d' association
sorgho
arachide ~ la profondeur de 60
cm suggere que
la competition entre ces
deux
cultures est plus forte ~ ladite profondeur.
9) Bien qu'etant tous deux des legumineuses, 1 'arachide, et le mucuna,
ont
eu
des
effets
opposes
sur
le
sorgho,
dans
les
parcelles
a association.
L' association sorgho/arachide a favorise le sorgho et deprime l ' arachide.
Ce qui
etai t
contraire
dans
I' association
sorgho/mucuna
ou
le
mucuna
a
exhibe
un
rendement significati vement
plus
eleve aussi
bien
en biomasse
qu' en
grains.
compare au mucuna en pur.
Cela etait particulierement vrai pour 1992.
10) une forte interaction entre pratiques de travail du sol/gestion des
residus de recolte et associations des
cultures a
ete observee,
interpellant
beaucoup a I ' entreprise
de
recherches
pluridisciplinaires
pour
repondre
aux
questions suivantes: quelles especes associer, ou, quand et comment?
Eu egard au rendement eleve du mucuna en biomasse vegetative, en azote et
en calcium,
cette culture merite d'etre
recommandee comme une composante des
strategies d'agriculture durable.
Son adaptation aux conditions
saheliennes
permettra de 1 'utiliser dans les systemes de production agro-sylvo-pastoraux pour
la restauration rapide et le maintien de la fertilite de nombreux sols degrades,
des jacheres comme des sols en culture, ainsi que pour la production de fourrage.
Du fait
de
sa
nature
volubile,
sa culture
en
association
presenterait
plus
d I inconvenients
que
d' avantages
pour
la
seconde
culture.
Par
contre,
son
utilisation
dans
les
cultures
en
bandes
serait
tres
recommandable
car
cela
faciliterait
les operations
culturales
tout
en permettant un systeme aise de
rotation et de lutter contre certains ravageurs.
Je me suis engage a continuer
le travail dans ce sens une fois de retour au pays.

SALlBO SOME
Effect of Intercropping and Tillage/residue Management on Plant
Competition for Water and Nutrients.
(1lnd2r the direction of DR. WILUAM L. HARGROVE)
Small-holding farmers in the tropics have traditionally intercropped their
lands under different tillage and residue management systems.
Yet, little
quantitative information is available about water use by intercropped species
grown under varying tillage and residue management systems.
To examine
the effect of intercropping and tillagelresidue management practices on plant
competition for water and nutrients, grain sorghum [Sorghum bicolor (L.)
Moench,cv. "Pioneer 8230"] was intercropped with peanut [Arachis
hypogaea L., cv. "Southern Runner"] nor velvet bean [Stizolobium
deeringianum Bort, vc. "Early Speckled Velvet Bean"] under conventional
tillage (CT), no-tillage with residue cover (NTC) or no-tillage bare (NTBl in
1991 and 1992. The parameters of concern were plant root growth, soil
water content, biomass production, and yield and soil properties.
Root length density (RLO) and root dry weight (ROW) were higher in NTC
and NTB than in CT, and this was largely attributed to higher soil moisture
content.
All combinations produced significantly more roots within the top
10 cm depth than deeper depths. Sorghum produced more roots followed
by velvet bean and peanut. Intercropping resulted -in intermediary root
production compared to the component sole crops.
Root growth was
greater in 1992 than in 1991, despite the reduced rainfall in 1992, and this
was attributed to stimulative effect of the water shortage and changes in
soil fertility.
The ratio of root weight to root length density suggested that
finer roots were produced in 1992 compared to 1991.
The measurement of soil water content by time domain reflectrometry
clearly confirmed the moisture disadvantage of conventional tillage over no-

tillage systems.
Crop residue removal from no-tillage plots resulted In
insignificantly less soil water content than otherwise. These differences
i
corroborate the water infiltration measurements. Reduced sOil water content
in mixtures suggested a more thorough soil exploration and a greater water
use by intercrops when compared to sorghum monocrop. Increased
competition for water between sorghum and either legume in the mixtures
appeared to occur at 45-60 cm soil depth.
In general, plant biomass production, nutrient uptake and grain yield
drastically decreased in the second year of the experiment as a result of
unfavorable rainfall distribution, late planting and reduced soil nutrient
content.
On the average, CT favOred plaRt biomass production, nutrient
uptake and yield in 1991 where rainfall distribution was satisfactory.
NTC
was advantageous under the drier conditions during the 1992 growing
season.
Although NTB differed little from NTC, soil nutrient content and pH
in NTB suggested that residue removal may lead to long-term soil infertility.
Velvet bean biomass production and nitrogen yield were interestingly high,
encouraging the use of this crop for improving soil properties. In general,
intercropping improved the residue quality and provided an overall yield
advantage over monocultures.
In general, the interactions between intercropping and tillage/residue
management systems were significant and complex, suggesting careful
selection of intercrops and soil management systems for satisfactory crop
production.
II\\IDEX WORDS:
Intercropping, Plant Competition, Tillage, Residue
Management, Water Infiltration, Plant Root Growth, Soil Water
Content, Sorghum, Velvet Bean, Peanut.

EFFECT OF INTERCROPPING AND TILLAGEIRESIDUE MANAGEMENT
ON PLANT COMPETITION FOR WATER AND NUTRIENTS.
by
SALIBO SOME
Approved:
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A i pog, Meda Agnes-Marie, a i bib'I'r, Some Sankaar, Nirsaalo, a ni
Amp6 Kpip6 yang nan ka i gne a tuo a gnan.
A i saan, Somda Nanwyir, le ti kp'ir ka ku m'an a nuor gnan. A nan wa ti ta
a gnan, i tiera ka i mi tu nan a nuor ti ta a le a i fang na ta. Naanmwin·le a ti
fang, ni a ti kpa tiere.
K'D wul m'an a sor ka kum'an a chaala ni a fang, ka i
tuon ko a i saan nuor 6 nana gman ko m'an, a i yeb, a i yeb-pouli, ni a
Naanmwin ti sa an pu vielu yang.
iv

ACKNOWLEDGEMENTS
This achievement would not have been possible without the friendship
and endless assistance from Mrs. Nancy Barbour in computer work during
the phase of my course work, Bill Nutt and Charlie Burnett in all field work,
Galen Harbers in the statistical analysis, Mrs. Debra Belvin in typing my
numerous tables and correcting my manuscript and Dr. Barbara Bellows for
editing the first drafts of my manuscript. Dr. Dan McCracken was a good
friend, whose advice and encouragement has been of tremendous
assistance. My committee members, Ors. W. L. Hargrove, D. E. Radcliffe,
O. E. Cummins, R. E. Lynch, and C. S. Hoveland, have supported and guided
my research project with excellence. Fro:n the start to the end of my
training, I have faced a multitude of difficulties. The support and
encouragement of my major professor, Dr. W. L. Hargrove, is no doubt the
key to the completion, making it fair to state that I have been sponsored by
the department of Crops and Soils Sciences at the Georgia Station. Or. and
Mrs. Oarl Snyder were very special friends and supporters. Also, Ms. Che F.
Ishaack will always be fondly remembered. To all of the above people, as to
all that I might have forgotten, who have directly or indirectly contributed to
this accomplishment, I express my profound gratitude.
v

TABLE OF CONTENTS
ACKNOWLEDGEMENTS
v
CHAPTER 1
INTRODUCTION
.
CHAPTER 2
LITERATURE REVI EW
6
CHAPTER 3
EFFECT OF INTERCROPPING AND
TILLAGE/RESIDUE MANAGEMENT
ON PLANT ROOT GROWTH
25
CHAPTER 4
EFFECT OF INTERCROPPING AND
TILLAGE/RESIDUE MANAGEMENT ON PLANT
COMPETITION FOR WATER
49
CHAPTER 5
EFFECT OF INTERCROPPING AND TILLAGE/RESIDUE
MANAGEMENT ON NUTRIENT UPTAKE, BIOMASS
AND YIELD PRODUCTION
78
CHAPTER 6
CONCLUSIONS
116
VI

SALlBO SOME
Effect of Intercropping and Tillage/residue Management on Plant
Competition for Water and Nutrients.
(Under the direction of DR. WILLlAM L. HARGROVE)
Small-holding farmers in the tropics have traditionally intercropped their
lands under different tillage and residue management systems. Yet, little
quantitative information is available about water use by intercropped species
grown under varying tillage and residue management systems. To examine
the effect of intercropping and tillage/residue management practices on plant
competition for water and nutrients, grain sorghum [Sorghum bicolor (L.)
Moench,cv. "Pioneer 8230"] was intercropped with peanut [Arachis
hypogaea L., cv. "Southern Runner"] or velvet bean [Stizolobium
deeringianum Bort, vc. "Early Speckled Velvet Bean"] under conventional
tillage (CT), no-tillage with residue cover (NTC) or no-tillage bare (NTB) in
1991 and 1992. The parameters of concern were plant root growth, soil
water content, biomass production, and yield and soil properties.
Root length density (RLO) and root dry weight (ROW) were higher in NTC
and I\\lTB than in CT in accordance with soil water measurements, and were
~~.,
als0Arvithin the top 10 cm depth than deeper. Sorghum produced more roots
followed by velvet bean and peanut. Intercropping resulted in intermediary
root production compared to the component sole crops. Water shortage
during the 1992 growing season seemed to simulate finer and more
extensive root growth -
.:ompared to 1991.
The measurement of soil water content by time domain reflectrometry
clearly confirmed the moisture advantage of I\\ITC over eT, and corroborated
the water infiltration measurements. NTB exhibited mean values.
Intercropping seemed to favor a more thorough use of soil water compared

to sorghum monocrop. A greater inter-crop competition for water was
observed at 45-60 cm soil depth.
On the average, CT was more productive in 1991 where rainfall
distribution was satisfactory, but NTC was advantageous under the drier
conditions of the 1992 growing season. Although NTB differed little from
Wt..
NTC, the decrease of soil pH and nutrient content", NTB suggested that
residue removal may lead to a long-term soil infertility.
Velvet bean showed
promise for improving soil properties.
Intercropping improved the residue
quality
and exhibited an overall yield advantage over
monocultures.
In general, the interactions between intercropping and tillage/residue
management systems were significant and complex, suggesting careful
selection of intercrops and soil management systems for satisfactory crop
production.
INDEX WORDS: Intercropping, Plant Competition, Tillage, Residue
Management, Water Infiltration, Plant Root Growth, Soil Water
Content, Sorghum, Velvet Bean, Peanut.

CHAPTER 1
INTRODUCTION
Conventional agriculture as practiced in developed countries entails
monocropping with intensive tillage and large inputs of synthetic fertilizers
and pesticides (Barrett, 198 -r, Follett and Walker, 1989; Batie and Taylor,
1990). As such, it is capital intensive, and depends on energy derived
mainly from non-renewable resources (Sanchez and Benites, 1987; Follet
and Walker, 1989; National Research Council, 1989).
Although this high-
input agriculture has spurred agricultural prod uction worldwide, its adverse
effects on the environment and human health raise concerns about the
sustainability of conventional agriculture (Barrett, 1981; Batie and Taylor,
1989; National Research Council, 1989).
A prominent component of conventional agriculture, monocropping
creates homogeneous agroecosystems that are highly vulnerable to pests
and diseases (Baker and Cook, 1974; Barrett, 1981). The disastrous potato
blight (Phytophtera infestans) epidemic in Ireland in the 1840's, and the
southern corn leaf blight (Helminthosporium maydis) epidemic in the U.S. in
the 1970's (Bezdicek and Granatstein, 1990) are historical illustrations of
the disease disadvantage of monocropping systems.
In uniform pure stand
communities, plants explore the soil at the same depth and have the same
1

2
peak demand for resources.
Monoculture therefore, encourages intra-
specific competition that can resulting in yield loss.
Use of commercial fertilizers to maximize yield has increased drastically
since the Second World War (Follen and Walker, 1984; Keeney, 1986). In
particular, the use of nitrogen fertilizers accounts for 30-40% of total crop
productivity (Wolfe and Minchin, 1984), with the United States as the
leading consumer (FAO, 1984, 1986).
In the United States about 50 kg N
was applied per hectare of arable land in 1985 (FAO, 1986).
Nitrogen
fertilizer inputs in excess of crop N requirement or poorly timed application
permit nitrate to concentrate in cropped soils and to leach to ground water,
raising environmental and health concerns (Hallberg, 1989; Keeney, 1986;
Follett and Walker, 1989).
Another prominent component of conventional agriculture, intensive
tillage, promotes water runoff and soil erosion, resulting in loss of soil
productivity, reduction in surface water quality, and the siltation of streams,
lakes and reservoirs. On many soils conventional tillage is unsustainable.
With the removal of topsoil, organic matter and nutrients are lost, exposing
subsoil which is frequently more acidic and usually less productive. In these
situations, loss of productive topsoil increases reliance on liming and
fertilization for continued agricultural production.
In many African countries, crops are produced on small holdings by
subsistence farmers using hand tools.
Such labor-intensive production
methods permit mixtures of different species or varieties to be grown
concurrently on the same parcel of land, a practice termed intercropping.
Crop diversification through intercropping can maximize resource utilization
and ensure yield security in the event of epidemics or water shortage

3
(Okigbo, 1990; Sanders, 1989; Ikeorgu and Odurukwe, 1989).
Interplanting legume with non-legume crops can forestall soil nutrient
depletion (Russelle and Hargrove / 1989). While non-legume crops deplete
soil-N, legumes and their rhizobial symbionts fix atmospheric N that can
supply crop N needs, and often build up soil N reserves. In addition,
intercropping benefits small farmers by providing them a way to grow a wide
array of crops required for household use, freeing them from the burden of
purchasing food and feed for livestock.
In many developing countries, growing populations, a shrinking resource
base / and inappropriate f}roduction methods combine to threaten the
sustainability of agriculture. Under current production practices in subhumid
regions of Africa, crop residues are often exported as feed, fuel, or building
materials, grazed or burned, exposing the soil to high thermal fluctuation,
and wind and rain erosion (Okiggo, 1980).
Such removal of crop residue
accelerates soil and nutrient depletion. Shifting cultivation systems that
once included alternate fallow periods for nutrient replenishment (Nye and
Greenland, 1960; Sanders, 1989; Okigbo, 1990) are now disappearing
rapidly, the result of increasing population pressure on land (Said, 1984;
Vierch and Stoop/ 1990). In many areas, agriculture has moved onto
marginal lands and fragile soils, further compounding soil degradation
(Malton, 1984; Sanders, 1989).
Unlike in developed countries, small
holders in developing countries often cannot afford inorganic fertilizers. The
overall result of inadequate cropping systems and residue exportation in the
absence of fertilizer application are drastic increases in soil erosion,
decreases in soil nutrient and organic matter contents, and an exacerbation
of soil acidity (Okigbo, 1980; Lal, 1987).
As is the case in developed

4
countries, many current agricultural production practices in developing
countries are also not sustainable.
Numerous alternatives have been proposed to sustain soil productivity
with little harm to the environment. Among these, carefully designed
intercrop systems and improved crop residue management practices are
being widely advocated (National Research Council, 1989; Russelle and
Hargrove, 1989; Batie and Taylor, 1990). A review by Okigbo (1969)
showed that crop residues efficiently protect the soil against wind and water
erosion, and high thermal fluctuations, allowing better plant growth (Lal,
1975; Harrison and La-l, 1979).
Another factor with potential for increasing sustainabllity, intercropping
can lessen intraspecific competition which consequently may improve the
efficiency of water and nutrient use by crops (Russelle and Hargrove, 1989).
In particular, the intercropping of legumes and cereals appear to be an
efficient strategy for sustaining soil fertility (Follett and Walker, 1989;
Russelle and Hargrove, 1989; Cook and BaK.er, 1983).
A recent review by
Russelle and Hargrove (1989) indicates that deep rooting species, including
some legumes, can be used to reduce nitrate leaching and retain N in the
system.
Intercropped deep-rooted species can also transfer subsoil water
and nutrients to shallow rooted companion crops (Nobel, 1991).
Although the benefits of intercropping appear obvious, careful analysis of
crop performance in mixed stands is limited.
Numerous factors affect crop
performance in mixtures (Lai and Lawton, 1962; Reedy and Willey, 1980;
Pleasant, 1982). Complex interaction among these factors add to the
scarcity of data to make it difficult to predict the performance of untested
intercrop mixtures. Reports of legume/cereal intercropping are especially

5
contradictory in this regard (Lai and Lawton, 1962; Pleasant, 1982; Wolfe
and Lazenby, 1973; Wolfe et al., 1982).
Additional field work is required to
identify suitable combinations for intercropping and their management
requirements for optimal intercrop prod uction.
Among the factors affecting
crop performance in mixtures, the effect of tillage and crop residue
management practices has not been well investigated.
The present work was designed to study the effect of intercropping grain
sorghum with peanut or velvet bean under conventional tillage, no-tillage
with residue cover, or no-tillage with residue removed, on root growth, soil
moisture depletion,-crop biomass production, yield, and soil properties.

CHAPTER 2
LITERATURE REVIEW
I. INTERCROPPING
Unlike monocropping, intercropping entails the growing of two- or more
crops on the same land, at the same time, in proximate but different stands
(Nyambo et al., 1980; Davis et al., 1986). Intercropping systems are
diverse and include mixed cropping, row cropping, patch cropping, relay
cropping and alley cropping (Francis, 1986). Because of the physiological
and morphological heterogeneity that characterize mixed communities,
mechanization of some cropping operations, like pesticide and fertilizer
application, and harvesting is difficult in intercropped systems.
Consequently, crop associations, except for relay cropping, are not common
in industrialized countries.
In contrast, small-holding subsistence farmers in
the tropics have traditionally intercropped their lands to minimize risks
associated with monocultures, and to assure stable income and nutrition
(Francis et al., 1975).
Advantages associated with intercropping include, 1)
yield security in the event of insect plagues, disease outbreaks, water
shortage, or flooding, 2) reduced plant competition for resources, 3) high
resource use efficiency, 4) yield advantage over monocropping, and 5)
6

7
reduced rate of soil nutrient depletion (Willey, 1979; Okigbo, 1980; Ikeorgu
and Odurukwe, 1989; Russelle and Hargrove, 1989). Despite the fragile soil
fertility in the tropics, agriculture has sustained life in these regions for
millennia, probably due in part, to the practice of intercropping.
INTERCROP COMPETITION FOR RESOURCES.
In crop monocultures, as in homogeneous plant communities generally,
individual plants-compete strongly when resources are limited, sifice
requirements of each member are roughly the same (Hamblin and Donald,
1974). In mixed communities, resource requirements are variable in space
and time, which minimizes both inter- and intra-crop competition (Huxley
and Maingu, 1978; Izaurralde et aI, 1990). In general, plant competition for
resources (light, soil water, nutrients, and carbon dioxide) occurs during all
or part of the growing season (Kurtz et al., 1952; Gomez and Gomez, 1983;
Russelle and Hargrove, 1989 ) and the productivity of each companion crop
is dependant on its ability to compete. The interaction among these factors
can result in significant yield loss in mixed cropping (Fisher, 1977; Izaurralde
et aI., 1990).
Competition for water and nutrients.
Kurtz et al. (1952) were among the first to report on intercrop
competition for water and nutrients. Recent reports by Schultz et al. (1987)
indicate that legumes can compete strongly with corn for nitrogen.

8
However, in most cases, grass crops such as cereals exhibit a much
stronger competitiveness than legume crops when the two are grown
together (Davis et ai., 1986\\.
During pasture development, Wolfe and
Lazenby (1973) noted that grasses were more competitive than white clover
for P uptake. Seedling forage legume growth was s"gnificantly reduced due
to competition from corn (Lefran<;:ois and Scott (1988).
Chang and Shibles
(1985) reported that corn strongly competed with cowpea for Nand P.
De
Queiro and Galwey (1986) intercropped five sorghum genotypes with two
cowpea genotypes, and reported that all sorghum genotypes affected the
cowpea perfo+mance. The effect of cowpea on sorghum was-less
noticeable. This domination often has been attributed to the extensive root
system of grasses which enables them to extract nutrients more efficiently
than legumes (Lai and Lawton, 1962; Wolfe and Lazenby, 1973; Caradus,
1980). In general, cereal/legume competition is most severe for legumes
during the early part of the season due to the slow root development of the
latter (Manson et aI, 1986).
As a result, legume intercrops often experience
slow early growth and reduced vigor (Pleasant, 1982; Wolfe et ai, 1982).
Davis et al. (1986) distinguished two categories of intercrop legumes
with cereals. One includes those which take advantage of temporal
differences between crops and the other, those which rely on spatial
differences. According to Davis et al. (1986), plant characters associated
with these two categories are time to maturity (temporal differences), and
plant architecture above and below ground (spatial differences).
The
severity of competition depends on a number of factors such as 1) soil
water and nutrient availability, 2) intercrop planting density and geometry, 3)
timing of planting, and 4) intercrop species or varieties (Willey et al., 1981).
t
l
r
I

9
Competition for water and nutrients is reduced in nutrient rich moist soils
(Willey et al., 1981), but increases with resource depletion (Gliessman,
1986; Izaurralde et ai, 1990).
However, many factors can reduce plant
competition for water and nutrients in intercropping systems.
Among them,
plant population of each intercrop species is generally lower than it is in
monoculture. Therefore, the risk of moisture stress may be reduced in
intercropping systems compared to monocultures. This is supported by
reports that sorghum was less susceptible to moisture stress in
sorghum/cowpea association than in pure stands (Andrews, 1973). Report
by Murry and Swensen (1985) clearly demonstrated the importance of
intercrop plant population on yield.
Winter pea ( E. sativum ssp.arvense L.)
mixed with 25% winter cereals (barley or wheat) yielded up to 27% more
seed than monocropped winter pea. In a reverse mixture, a 60% yield
decrease was recorded for winter cereals. In a barley/pea intercropping,
lzaurralde et al. ('1990) reported that barley yield decreased linearly with
increasing pea density.
Andrews (1973) indicated that successful growth of
peanut in mixtures requires either a low population of the other crop, or
crops with a longer growth cycle planted after peanuts are established. This
observation agrees with the critical nature of time of planting of component
crops in associations stressed by Francis et al. (1985).
Another factor that can red uce plant competition for water and nutrients,
complementary root systems of intercrops permit more efficient use of water
and nutrients and, therefore, greater ability to withstand short falls in
precipitation. In the experiment by Andrews (1973) sorghum withstood
moisture stress in mixture with cowpea partially because it was deeper

10
rooted, which created a spatial difference in resource utilization that
reduced competition from cowpea.
In relay cropping systems in particular, where the growth periods of
crops overlap only slightly, inter-crop competition may be minimal (Francis et
al., 1985; Francis, 1986; Russelle and Hargrove, 1989). In any case, when
time of planting is adjusted so that legumes overcome the competition from
cereals, intercropping with legumes can benefit cereals by providing them
with a nitrogen source (Agboola and Fayemi, 1972; Francis, 1986; ).
Where spreading species such as Florunner peanut, cowpea or velvet
bean are intercropped, ground coverage by the canopy may reduce water
loss by evaporation enough to permit crop survival during drought periods or
conserve more water for succeeding relay crop.
Crops are very variable in their rooting patterns and include deep and
shallow rooting species (Gregory, 1988). Use of deep rooting intercrop
components can result in tapping deeper horizons and bringing up water and
occur whenever the soil water
reverse flow of water from the root to the soil matrix.
Blevins (1987) and
Corak et al. (1987) reported that such transfer of subsoil water from alfalfa
was enough for corn to survive a 100 day drought.
According to Agboola
and Fayemi (1972) legumes also have the potential for excreting fixed
nitrogen for companion crop uptake. Se ne seed legume roots during the
growing season may also decompose rapidly enough to supply nitrogen to
t
I
l
I

1 1
companion cereals. Thus, these phenomena reduce intercrop competition
and can improve water and nutrient use efficiency (Reddy and Willey, 1980;
Natarajan and Willey, 1980).
Competition for water and nutrients is reflected by the dynamics of the
soil moisture and nutrients in the root zone or soil profile. Where these
resources are limiting, lower plant density is generally recommended to
minimize yield loss. For the majority of crops, little information is available
concerning their reaction in intercropping systems .
. Competition for light.
Light interception by the plant canopy depends on the leaf area index
(LAI). In intercropping systems, above ground spatial differences among
associated crops favors the development of an increased leaf area index
(IRRI, 1975). As a result, light use efficiency is expected to be higher in
mixed than in pure stands. Willey and Osiru (1972) attributed yield
advantage of their mixtures to more efficient utilization of light that arose
from the complementarity of crop heights.
However, this advantage is not
always observed, especially when planting geometry is inadequate, as in
large/small crop associations where shading effects from larger crops are
more likely.
In peanut/cereal mixtures for instance, shading from cereal
intercrops contribute to depress peanut yield (Koli, 1975; Stirling et ai,
1990). Light interception by sorghum or millet in mixtures with green-gram
contributed to yield loss by the latter (Keswani and Mreta, 1980). Shading
effect is more deleterious during critical growth stages of the short intercrop
(Stirling et ai, 1990).

12
Despite the shading effects, the combination of short and tall species is
believed to improve the overall light use efficiency.
Although it may not be
important under moisture stress condition, improved light use efficiency can
reduce yield loss under nitrogen stress (Reddy and Willey, 1980). Light use
efficiency in intercropping can be improved by the complementarity of leaf
area indices in space and time.
In sorghum/millet mixture for example,
Kassan and Stockinger (1973) found that rapidly expanding leaves of millet
intercepted most of the light early in the season.
Slower growing sorghum
leaves took over later as the millet ripened. Accessibility of the short
component intercrop to light depends on the plant density, height, leafiness
(Liebman and Robichaux, 1990), and leaf orientation (Nobel, 1991) of the
tall component. Intercropping species with good complementary effect is
recommended to minimize competition and yield loss (Dalal, 1974; De and
Singh, 1979; Willey and Reddy, 1981; Gomez and Gomez, 1983; Russelle
and Hargrove, 1989).
11. INCIDENCE OF DISEASES AND INSECTS
IN INTERCROPPING SYSTEMS.
Numerous examples of disease limitation in crop mixtures, compared with
pure stands have been reported (Wolfe and Minchin, 1982; Ikeorgu et al.,
1984). Historically, crop association has contributed to the control of barley
and wheat mildews in the United States (Wolfe and Minchin, 1982;
Wagstaff, 1987). Peanut grown in combination with beans showed less
severity of leaf spot disease and rosette than in pure stands (Mukiibi, 1980).
Damage by flies, midges and aphids to sorghum was reduced when sorghum

13
was grown in association with simsim (Kato et al., 1980). In maize/cowpea
mixture, cow pea yield was improved as a result of reduced insect pest
invasion (Karel et al., 1980). Similar results were reported for beans in
mixture with maize (Rheenen et al., 1980.
Clifford et al., (1989) reported
lower numbers of cassava whiteflies in cassava/cowpea systems than in
cassava monoculture.
Mechanisms by which diseases and insects are reduced by mixtures are
not well documented.
Because the population is genetically homogeneous,
monocultures are highly prone to epidemics that can lead to economic
disasters (Bezdicek and Granatstein, 1990).
In mixed communities, genetic
diversity is higher and damage by polyphagous pests is reduced on individual
intercrop component (Chin, 1979).
In addition, non-matching hosts behave
as barriers to monophagous invaders and limit their spread within the
community.
Mixed stands can also result in a greater complexity of the soil
microbial population, which could decrease the rate of invasion by foreign
organisms (Cook and Baker, 1983).
In many intercropping systems, wind
velocity is reduced, which in turn, reduces the rate of pathogen propagation
(Keswani and Mreta, 1980). By intercropping species with different above
ground morphologies, aeration may be improved, influencing humidity and
thermal and gas exchange conditions, and reducing the severity of some
diseases.
Ill.
YIELD PERFORMANCE IN INTERCROPPING SYSTEMS
Yield performance in mixtures is well documented. In general,
intercropping decreases individual intercrop yields with higher effect on

14
legume crops (Davis et al., 1986).
Izaurralde et al. (1990) compared
barley/field pea intercropping with the respective sole cropping of the
intercrops for grain and N yield. They reported that each intercrop yielded at
half its sole rate.
Intercropped-barley especially, yielded 35 to 40% lower,
but its grain and straw N content were higher than in pure stand. In
legume/cereal mixtures, Nyambo et al. (1980) reported a yield reduction of
33-82% for their legume and only 7-37% for cereal intercrops. Even with
less disease infection, intercropped sorghum and millet yielded less than
their pure stands (Keswani and Mreta, 1980). Peanut yield reduction in
mixture with cereals' is-particularly weel documented (Koli, 1975; IRAr;
1978; Ikeorgu and Odurukwe, 1989).
However, many intercropping systems, particularly cereal/legume
combinations, show an overa II yield advantage over monocultures (Sanchez,
1976; Fisher, 1977; Nyambo et al., 1980; Ikeorgu and Odurukwe, 1989).
Nyambo et al. (1980) reported a 60% overall yield increase in mixtures
compared to monocultures. In Senegal, sorghum/peanut intercropping gave
higher overall yields than the individual crops in pure cultures (Schilling,
1965). Yield advantage of intercropping systems depends on the nature of
competition among plants, which in turn, depends on resource availability,
cropping strategy, and the nature of the crops in association (Barker and
Francis, 1986).
IV. EFFECT OF RESIDUE MANAGEMENT ON SOIL PROPERTIES
No-tillage and resid ue mulches are efficient strategies for soil and water
conservation (Okigbo, 1969; Lal, 1975). Crop residue mulches absorb the

15
kinetic energy of raindrops, protecting surface soil aggregates from break
down and dispersal. Consequently, surface sealing or crusting, water runoff
and soil erosion are reduced (Russelle and Hargrove, 1989). In addition,
crop residue mulches reflects solar radiation, reducing thermal fluctuations,
and forestalling water evaporation (Lal, 1975; Harrison and Lal, 1979).
Reduction of thermal amplitudes by a stubble layer was efficient enough to
limit self-mulching effect of a vertisol (Dexter et al., 1982). Crop residues
also behave as refuge and/or food resource for soil-dwelling animals, whose
activities improve soil macroporosity and hydraulic conductivity (Kemper et
al., 1987).
Earthworms and termites also contribute to soil mixing and -
aggregate stabilization.
In contrast to no-tillage, conventional tillage encourages surface crusting,
resulting in greater water runoff and soil loss (Russelle and Hargrove, 1989).
Although conventional tillage may loosen the soil for better plant rooting, its
tendency to reduce water infiltration and its lack of a moisture conserving
surface mulch may significantly reduce soil plant-available water in dry
areas, and cause greatly diminished yields.
Regardless of tillage, nutrients are recycled when crop residues are
returned to the soil (Thompson et al., 1985). When crop residues are
removed, a practice common in many parts of Africa, nutrient recycling is
not only prevented, but many of the advantages obtained with a reduction in
tillage systems are also eliminated.
No-tillage with residue removal speeds
up soil degradation, and quickly reduces crop production (Hewitt and Dexter,
1980; Dexter et al., 1982; Utomo and Dexter, 1981). Hewitt and Dexter
(1980) showed that soil bulk density throughout the growing season was
greater in burned no-tillage than in conventional tillage, burned or not.

16
Under no-tillage, roots were heavily concentrated in the upper 15 cm,
presumably due to soil compaction.
Although it is widely practiced, no-
tillage with residue removal has received little attention from researchers,
and information is lacking about the effect of such practices on crop
production in intercrop systems.
V.
LEGUME NITROGEN FIXATION AND USE EFFICIENCY
Nitrogen is a critical element in plant nutrition. Nodulated legumes can
symbiotically fix a su-bstanhal amount of atmospheric nitrogen (McGuire et-
al., 1989; Gibson et al., 1977).
A portion of this fixed N typically becomes
available to non N-fixing crops grown in association with legumes (Russelle
and Hargrove, 1989; Fyson and Oaks, 1990; Hargrove, 1986). Nitrogen
derived from N fixation amounted to about 33% in soybean and cowpea
(Sisworo et al., 1990). Suwanarit et al. (1986) reported that 55-66% of the
N produced by peanut and soybean was fixed.
Plant nitrogen fixation is
higher in N-poor soils especially when plants are inoculated with effective
bacterial symbionts. However, recycling of legume-N recovered by non-
legume crops depends on a number of factors including the rate of
mineralization, the quality of the residue (lignin and N content, C/N ratio),
and the soil moisture status (Sisworo et al., 1 990). This percentage also
reflects the subsequent cereal crop N-use efficiency (NUEj from legumes
(NUEL), which is typically far lower than the NUE from fertilizer (NUEF). For
example, it has been shown that only 10 to 30 percent of legume-N was
recovered by the following crop (Ladd and Amato, 1986; Harrison and
Hesterman, 1987), compared to recoveries from fertilizer N of 30 to 70

17
percent (Stanford, 1987). Typically, high NUEF's arises because fertilizer N
is readily available for plant uptake.
In contrast, a large portion of legume-I\\J
remains in the soil organic matter and biomass pools, and only becomes
available after mineralization.
The estimation of NUE that is based on data from a single season, favors
fertilizers, and tends to discourage the use of legumes as a reliable N source.
This concern was raised by Bezdicek and Granatstein (1989) who suggested
that the. efficiency of both N sources be evaluated over a longer time period
to develop a total N budget of inputs (N fertilizer, N2 fixation, or N
deposition), and outputs (harvest, leaching, volatilization, denitrification).
Meisinger (1984) also suggested that estimation of changes in N pool sizes
(e.g., organic matter, microbial biomass, inorganic N, etc.) be made when
comparing NUE between legumes and fertilizers.
Taking into account
changes in soil N that take place when legumes are used for many years
could drastically increase estimates of NUEL and drastically improve the
adoption of legume N sources for crop production.

18
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22
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Academy Press, Washington, D.C. PP. 448.
Nobel, P.S. 1991. Physicochemical and Environmental plant physiology.
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Okigbo, B.N. 1990. Sustainable agricultural systems in tropical Africa. PP.
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23
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24
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A field technique for separating
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development of heterogenous cropping. P. 95-104. ill: E.J. Gallagher

CHAPTER 3
EFFECT OF INTERCROPPING AND TILLAGE/RESIDUE
MANAGEMENT ON PLANT ROOT GROWTH.
ABSTRACT
Plant competition for below ground resources is controlled by numerous
factors that interact dynamically. The complexity of these interactions
complicates the determination of compatible crops for association under
varying conditions. In tropical areas, lands are traditionally intercropped
under a variety of tillage and residue management practices with a
corresponding variation in yield.
The effect of intercropping sorghum
[Sorghum bicolor (L.) Moensh, cv. "Pioneer 8230"] with peanut [Arachis
hypoqaea L. cv. "Southern Runner"] or velvet bean [Stizolobium
t
deeringianum (Bort), cv. "Early Speckled Velvet Bean"] on root growth under
different tillage/residue management practices was studied in Griffin,
Georgia, during the summers of 1991 and 1992 using a split-plot design in
randomized complete blocks. Three tillage management systems were
examined: conventional tillage (CT), no-tillage with residue cover (NTC) and
no-tillage bare (NTB). Root growth was examined as a n indicator for crop
competition for below ground resources. The experimental design was a
25

26
randomized split-plot, with tillagelresidue management as the main plot and
crop treatment as the sub-plot. Root samples were taken from the middle of
inter-row spaces at 0-10 cm and 20-30 cm soil depth. Results indicated
that root growth was reduced in CT compared to NTC and NTB, and this
was in accordance with the measurements of soil water content.
Sorghum
produced significantly more roots than either legumes under all
tillagelresidue management systems. Root production in mixtures was
intermediary between the corresponding sole crops. Based on these results,
intercropping appeared to favor sorghum over the legumes for water and
nutrient uptake. For all main treatments, ooth root length density (RLD) and
root dry weight (RDW) were higher at the 0-10 cm than at the 20-30 cm
soil depth. Despite the reduced rainfall recorded during the 1992 growing
season, crops produced more roots in comparison to 1991, and this was
attributed to probable stimulative effect of the water shortage and reduced
soil fertility.
The ratio of RDW to the RLD suggested that finer roots were
produced in 1992 compared to 1991.
INTRODUCTION
Plant water and nutrient uptake is influenced by root morphology and
physiology (Gregory 1988; Klepper, 1992).
In general, monocotledons, such
as cereal crops, have extensive fibrous root systems. This permits them to
explore a large volume of soil, thereby increasing their ability to compete for
below ground resources (Russell, 1977; Klepper, 1992).
Sorghum root

27
growth, can extend beyond 135 cm sOil depth, with maximum root density
within the top 15 cm depth (Gregory, 1988; Doggett, 1988; Roder et al.,
1989). Dicotyledons, including legumes, have root systems ranging from
fibrous to centralized taproot (Russell, 1977; Klepper, 1992). Peanuts in
particular, have a deep taproot and fine lateral roots with maximum root
density within the top 15 cm of soil (McCloud, 1974; Lenka and Misra,
1973; Kenneth et al., 1982; Pandey et al., 1984). Excluding the taproot,
peanut root distribution was found to be uniform below the row and laterally
-
46 cm from the row (Robertson et ai., 1979). Rooting depths to 200 cm
often have been reported for peanut (Hammond et al., 1978; Robertson et
al., 1980).
Kenneth et al. (1982) reported deeper rooting depths for
Florunner peanuts on a sandy soil. In contrast to peanut, the rooting pattern
of velvet bean has not been fully investigated.
Hulugalle (1984) sampled
velvet bean roots randomly to only 30 cm depth and reported a greater root
density in the top 10 cm than in deeper depths. During the same
experiment, velvet bean produced more roots than cowpea but less than
corn.
Plant root growth is controlled by soil physical and chemical properties,
which often are affected by tillage and crop residue management practices
(Mosher and Miller, 1972; Cooper, 1973; Hulugalle et al., 1984; Blevins et
aI., 1984; Phillips, 1984; Shopart, 1987; Payne and Gregory, 1988;
Gregory, 1988; Haynes and Knight, 1989; Klepper, 1992; Zobel, 1992).

28
Changes in these properties may influence niche-breath overlap and crop
competition for below ground resources. Soil physical properties that affect
plant rooting include soil temperature, water content, compaction and air-
porosity (Mosher and Miller, 1972; Cooper, 1973; Klepper, 1992; Phillips,
1984). An extensive review of the role of soil temperature on root growth is
provided by Cooper (1973).
A recent review by Klepper (1992) showed that
both the number and pattern of root branching are partially controlled by
temperature.
Mosher and Miller (1972) found that warmer temperatures
caused vertical root elongation, while cooler temperatures stimulated
horizontal orientation. In general, mulched soils, such as no-tillage with
residue cover (NTC), have cooler temperatures than soil under conventional
tillage (CT) and no-tillage with residue removed, i;e, no-tillage bare (f\\ITB)
(Lal, 1975; l\\JeSlIlith et al., 1984; Phillips, 1984; Gupta et al., 1984;
Shopart, 1987; Payne and Gregory, 1988). With regard to results of
Mosher and Miller (1972), the cooler temperatures in the NTC may suggest
greater horizontal root development and therefore, increased root density in
the inter-row spaces in NTC as compared to CT or NTB.
Although soil compaction is a common root growth limiting factor in no-
tillage systems (Voorhees, 1992), increased soil water content in NTC
(l\\JeSmith et al., 1987; Lal, 1975; Phillips, 1984), can favor greater root
growth compared to CT and NTB (Hamblin, 1985). However, complex
interactions from numerous other factors can also result in non-linear

29
responses of root growth to soil moisture content (Klepper, 1992; Zobel,
1992). For instance, water stress imposed to peanut at different growth
stages resulted in increased root growth as compared to optimal moisture
treatment (Meisner and Karnok, 1992).
Also, in extreme moisture
cond itions, sOil aeration is red uced, limiting root growth lBrady, 1974).
Prihar et al. (1989) reported that water and nutrients also can substitute for
each other.
Soil chemical properties controlling root growth in the field include soil
-
pH, aluminum toxicity and nutrient availability (Tisdale et aI., 1985;
Wilkinson and Duncan, 1989; Shuman et al., 1990; Zobel, 1992; Voorhees,
1992; Foy, 1992). The impact of each of these factors on root growth is
species dependent (Gregory, 1988; Roder et al., 1989; Foy, 1992).
Wilkinson and Duncan (1989) indicated that soil pH below 4.8 results in H+
ion toxicity for sorghum grown on acid soils in Georgia. Below pH 4.5
aluminum toxicity becomes more important than H+ toxicity (Shuman et al.,
-1990; Foy, 1992t, Peanut, on the other hand,can tolerate soil pH levels as
low as 4.3 (Laurence, 1973). Morris and Pierre (1949) reported high
tolerance of peanut to AI and Mn toxicity.
Soil chemical properties are also greatly influenced by tillage and residue
management practices (Lal, 1977).
Nutrient cycling processes and
microbiological activities are different when comparing CT, NTC and NTB
(Wilson and Hargrove, 1986; Monchoge and Mwonga, 1988; Smith and

30
Sharply, 1990). Whether residues are incorporated, like in CT or left on the
surface, like in NTC, nutrients are recycled, and organic matter is returned to
the soil with more rapid turn over in CT (Lal, 1977; Wilson and Hargrove,
1986; Smith and Sharpley, 1990; Guertal et al., 1991).
Rapid release of
plant nutrients in CT may be sufficient to reduce inter-crop competition.
Also, the return of organic matter to the soil may contribute to reduce soil
acidification (Blevins et al., 1984).
When crop residues are removed from
the field as in NTB, large quantities of cations such as Ca 2 + and Mg 2 ' are
-
also removed, which can eventually result in increased soil acidity and
aluminum toxicity. Changes induced by tillage and residue management
practices may be significant enough to affect plant root growth and
many commonly used mixtures being grown under usual tillage and crop
residue management systems.
According to Russell (1977), plant root
growth is forced by increased intra-crop competition with rows to extend to
the inter-row spaces for more uptake, making it possible to measure inter-
crop competition for below ground resources by sampling soil in the middle

31
of the inter-row space for available nutrients, soil moisture content, or root
density.
This paper provides measurements for the effect of intercropping grain
sorghum [Sorghum bicolor (L.) Moench,cv. "Pioneer 8230" ] with peanut
[Arachis hypogaea L., cv. "Southern Runner"], or velvet bean rStizolobium
deeringianum Bort. cv. "Early Speckled velvet bean".] on root growth under
three tillage management systems: CT, NTC, and NTB.
MATERIALS AND METHODS
Experimental design
A field study was conducted in summer 1991 and 1992 on a Cecil sandy
clay loam at Griffin, Georgia. Following a long fallow during which grasses
. were the predominant vegetation, the soil was 'planted to potato for one
year, then wheat for 2 years prior to this experiment. In the summer of
1990, wheat residues were removed, and soil was conventionally tilled to
30 cm soil depth before planting forage sorghum over the entire area. This
was done to reduce spatial differences and further depress soil nutrients in
order to better observe treatment effects.
After harvest in early October
1990, the experiment was laid out as a split-plot design in randomized

32
complete blocks with 3 replicates.
Main-treatments, which were
immediately applied consisted of conventional tillage (CT), no-tillage bare
(NTB), and no-tillage cover (NTC).
Main treatments were re-applied about
two weeks after harvest in 1991 for the 1992 experiment. Subplot
treatments were applied at planting, and consisted of pure stands of
fertilized (SF) and unfertilized (S) grain sorghum [Sorghum bicolor (L.l
Moench, cv. "Pioneer 8230"], peanut [Arachis hypogaea L., cv. "Southern
Runner"] (G), velvet bean [Stizolobium deeringianum Bort, cv. "Early
-
Speckled velvet bean] (V), and mixed stands of sorghum/peanut (SG), and
sorghum/velvet bean (SV).
Grain sorghum and peanut were used because:
1) they are very important as food and cash crops and
2) they are often
intercropped in tropical Africa.
Velvet bean was used because of its
potential for fixing nitrogen and producing heavy biomass for soil
improvement (Scott, 1946;
Burle et al., 1992). NPK fertilizer was hand
broadcasted in SF treatment respectively at rate of 90 kg N/ha, 45 kg
P 0s/ha, and 67 kg K 0/ha about 20 days after emergence. Crops in
2
2
mixtures were planted in alternate double rows. Each subplot consisted of 8
rows, 75 cm apart and 12 m long.
Plants were about 10 cm apart within
row.
Plant populations for all crops averaged 200,000 and 100,000 plants
per hectare in pure and mixed stands respectively. Weeds were controlled
as needed during the growing season by hoeing and during the winter period
by application of 0.56 kg/ha paraquat (1,1' dimethyl-4,4'-bibyridinium ion).

33
Crops were planted on June 1 and on June 15 in 1991 and 1992
respectively (figure 1).
Annual rainfall was 1126 and 14790 mm for 1991
and 1992 respectively, indicating a 31 % difference between the two years.
However, daily rainfall distribution presented in Figure 1, Chapter 3 for both
growing seasons clearly show an early water shortage recorded from mid
June to mid July 1992, compared to 1991, indicating that crops were
advantaged in 1991 compared to 1992.
Root sampling
Soil was sampled at depths 0-10 cm and 20-30 cm using a 5.5 by 10 cm
stainless steel ring. Two soil cores were taken randomly in the middle of
inner-most intercrop row space of each subplot and combined to make a
composite sample.
Samples were taken at approximately 25, 55 and 80
days after planting during each growing season.
These dates correspond
respectively to the 2nd (collar of fifth leaf visible), 5th (maximum growth:
booting, maximum leaf area, peduncle elongation), and 8th (3/4 of grain dry-
matter accumulated) growth stages of sorghum (Duncan, 1983). Samples
were immediately stored at _15°C until processing. Prior to root washing,
samples were allowed to thaw completely at room temperature. Roots were
washed by the hydropneumatic elutriation system (Smucker et al., 1982)
and hand cleaned with care to separate dead roots and trash from the fresh

34
roots.
A computer controlled digital scanning microdensitometer (Voorhees
et al., 1980) was used to measure root length index, which was converted
to actual root length using a computer program. For better scanning, roots
were stained in methyl violet solution for at least 24 hours. Data were
statistically analyzed by analysis of variance by year, by date of sampling, by
tillage/residue management system, by intercrop and by depth (SAS
Institute, 1985).
RESULTS AND DISCUSSION.
The data presented in Tables 1, 2, 3 and 4 clearly show that all crop
combinations produced more roots in 1992 than in 1991.
Although root
growth is commonly believed to be enhanced by soil water and nutrient
availability (Tisdal et al., 1985, Gregory, 1988)/ mild water or nutrient
stresses also can stimulate root production "for more uptake (Nobel, 1991),
Reduced rainfall during the first half part of the 1992 growing season (Figure
1) might have induced extensive root production for greater water uptake.
In addition, soil nutrient content decreased after the first season (Chapter 5),
presenting another possible reason for increased root growth. Despite the
increased root growth in 1992, the ratio of the root dry weight (RDW) to the
root length density (RLD) tended to be lower for 1992 compared to 1991

35
(Table 5), indicating that more tine roots were produced in 1992 compared
to 1991.
RLD and RDW were significantly higher in NTC and NTB than in CT. NTC
and NTB often were not significantly different.
Similar differences were
observed when these tillage/residue management systems were compared
for soil moisture content (Chapter 4), indicating that soil moisture was a
leading factor in root growth. According to Mosher and Miller (1972),
warmer soil temperatures stimulate vertical orientation of root growth while
cooler temperatures favor horizontal orientation. Since residue cover reflects
solar radiation and high moisture content increases the specific heat
coefficient of the soil, mulched soils in NTC would normally have cooler soil
temperatures compared to bare soils in CT or NTB (Lal et aI., 1977; Shopart,
1987; Gupta et al., 1984; NeSmith et al., 1987; Payne and Gregory, 1988).
If this was the case during this experiment, this may have contributed to
observed differences in plant root densities between CT and NTC. However,
no measurements of soil temperature was taken to substantiate the above
speculation. Insignificant difference found between NTC and NTB further
confirms the predominant role played by soil moisture content.
When crops were compared (Tables 1 and 2, and Figure 2), the sorghum
RLD was significantly higher than that for either legumes, agreeing with
numerous previous reports on cereal/legume root production (Gregory, 1988;
Klepper, 1992). The difference between sorghum and legume RLD was

36
particularly true when the sorghum was unfertilized. Reduced sorghum root
proliferation in the fertilized treatment may be due to reduced competition
for added nutrients. The greater biomass and grain yield production caused
by fertilization (Chapter 5) suggests that the sorghum plants invested less on
root growth in favor of yield production in the presence of the added
nutrients.
Velvet bean RLD was insignificantly higher than that for peanut.
Intercropping sorghum with either legumes resulted in intermediate average
root proliferation compared to the corresponding sole crops. This was
particularly true under NTC or NTB in both years. In CT, however, all crop
treatments were comparable with regards to RLD except for peanut
monocrop which remained significantly inferior to the other treatments.
The high competitiveness of intercropped cereal species often has been
attribute to their extensive rooting systems (Lai and Lawton, 1962; Mays,
1980; Caradus, 1980). However, the apparent rooting advantage of
intercropped cereals has not been clearly sUbstantiated. The ratios of RLD in
pure stand to the RLD in the mixture (Table 4) can provide an indication of
the competition pressure resulting from sole cropping compared to
intercropping (CPS/I)' A high CP SiI such as that observed for sorghum may be
indicative of 1) neutralism (neither crop affects the other), 2) amensalism
(one crop is inhibited and the other is not affected) 3) mutualism (both crops
may be affected to some extend as a result of obligatory interaction)

37
(Francis, 1986). Also, the root growth was so low for the legumes
compared to sorghum that even an enhancement in the mixture may not be
detected by use of the CP
alone. Therefore, a protocooperation
SII
(interaction favorable to both crops) also could have prevailed. The same
interpretation can be made regarding the reduced CP
for the legumes
SII
(Table 4). However, the actual measurements in the mixtures tended to be
less than the averaged mean values of the intercrop components (Table 1)
indicating that some inhibitory factors prevented maximal intercrop root
growth. The reduced yield for both intercrops (sorghum/peanut mixtures) or
for one of the intercrops observed in this experiment (Chapter 5), as also
reported by numerous authors for various cereal/legume intercropping
systems (Lai and Lawton, 1962; Reddy et ai., 1980; Hikam et al., 1992)
also seems to corroborate the existence of root growth reducing factors in
the mixtures. However, similarity in the interpretation of the CPSiI' the
resulting effect of all of the possible interactions indicated above may be
I
opposite for the sorghum anr the legumes.- Assuming that RLD is an index
f
of the degree of plant competition, a high CP
for sorghum would indicate
S/1
I
that inter-crop competition pressure was reduced for sorghum in the
mixture, compared to the intra-crop competition pressure in the pure stand.
f
In other words, sorghum was favored by intercropping compared to
I
monocropping. The same reasoning would lead to the conclusion that the
legumes were rather disadvantaged by intercropping compared to
I
I
I·
t

38
monocropping. Again, assuming that root growth is the major parameter for
measuring competition pressure, the comparison of the CP
permits to state
S/1
that sorghum was favored over either legumes in the mixtures.
The combined effect of high soil water and nutrient content near the soil
surface in NTC and NTB (Chapter 4 and 5) probably resulted in significantly
greater root growth in the 0-10 cm than in the 20-30 cm soil depth in both
years (Table 2).
However, soil compaction also may have been an important
factor in the soil profile root distribution.
In the CT where soil was loosen
and mixed in the plow layer, a greater proportion of the roots was observed
in the 20-30 cm soil depth, compared to NTC and NTB. This may have been
further encouraged by the dry condition of soil surface in CT (Chapter 4).
Similar results have been reported for a variety of crops (Gregory, 1988;
Arora et al., 1991; Meisner and Karnok, 1992).
CONCLUSION
Results from this study further confirmed the effect of tillagelresidue
management on crop root growth.
RLO and ROW were higher in NTC and
NTB than in CT, and this was in accordance with the soil moisture status of
these main treatments.
Regardless of the crop combination, root growth
was significantly greater within the top 10 cm depth than deeper. Sorghum

39
produced more roots followed by velvet bean and peanut. Intercropping
resulted in intermediary root proliferation compared to component sole
crops, and tended to favor sorghum over the legumes.
Despite the reduced
rainfall, the root growth was greater in 1992 compared to 1991 where
rainfall was high. This was attributed to stimulative effect of the water
shortage and changes in soil fertility.
The ratio of root weight to root length
density suggested that finer roots were produced in 1992 compared to
1991.

;'
Cll
,
§
:: ~ :::
f:$
..,
o
!.
C
.,.
..
._
c
_
f")
-
e
&:I.
C;I
Tabie~}. ~Effect of)n~'Tcropping and crop residue management on plant root growth for year 1991 and 1992.·
"c~§y
:!R:02.1~
CP
NTCc
NTB<
Average
TREATMENP
RLO
ROW
RLO
ROW
RLO
ROW
RLO
RDW
1991
SF
2.16a (b)
3.37a la)
4.10ab la)
5.07a la)
3.43a lab)
3.83a la)
3.23a
4.09a
S
2.35a Ib)
3.89a la)
4.30a la)
4.06a la)
3.05ab lab)
4.06a la)
3.19a
4.11 a
SG
1.31 b la)
2.32b la)
2.40bc la)
3.08bc (a)
1.43c fa)
1.93c la)
1.71 b
2.44b
SG
1.46
2.61
2.66
3.20
1.70
2.55
1.92
2.84
G
0.56c lab)
1.33c lab)
1.01 cd la)
2.34c la)
0.34c Ib)
1.03b Ib)
0.64c
1.56b
SV
1. 16bc la)
2.31b la)
1.38cd la)
2.25c la)
1.69bc la)
2.24b la)
1.41 be
2.27b
SV
1.58
2.89
2.42
2.91
1.97
3.01
1.97
2.99
V
0.80bc la)
1.89bc la)
0.54d la)
1.75c la)
d.88c la)
1.96b la)
0.74c
1.87b
Average
1.35b
2.47ab
2.17a
3.02a
1.74ab
2.40b
1992
SF
1.56b Ib)
2.51 a Ib)
4.12b la)
3.31 be Ib)
4.04b la)
4.57abc la)
3.24bc
3.44b
S
2.10ab Ib)
2.70a Ib)
10.63a la)
5.54a lab)
17.04a la)
6.99a la)
9.93a
5.08a
SG
2.23ab la)
2.29a la)
5.62ab la)
4.08ab la)
2.53b Ib)
3.09bc la)
3.46bc
3.15b
SG
1.10
1.59
5.45
3.33
9.58
4.72
5.38
3.22
G
0.09b Ib)
0.48b la)
0.27b lab)
1.12c la)
2.11 b la)
2.44c la)
0.82c
1.35c
SV
3.14a la)
2.99a la)
3.31 b la)
3.15bc la)
8.51bla)
5.35ab la)
4.99b
3.83b
SV
2.16
2.75
6.38
4.22
10.64
5.93
6.36
4.07
V
2.22ab la)
2.80a la)
1.92b la)
2.89bc la)
4.24b la)
3.47bc la)
2.79bc
3.05b
Average
2.09b
2.38b
4.35ab
3.41 a
6.19a
4.29a
·Means within column for each year with same letter without parentheses are not significantly different la = 0.1).
Means within row with same letter in parentheses are not significantly different la = 0.1).
bSF = fertilized sorghum; S = unfertilized sorghum; SG = sorghum/groundnut mixture; etc.
<CT = conventional tillage; NTC = no tillage with crop residue; NTB - no tillage with residue removed.
SG = mean for sorghum and groundnut monocrop; G = groundnut monocrop; V = velvet bean monocrop
SV = mean for sorghum and velvet bean intercrops; RLO = root length density; ROW = root dry weight

Table 2.
Plant root growth parameters at two depths under different tillage and residue management systems for year 1991 and
1992.
CT
NTC
NTB
Average''''·
Depth #
RLO·
ROW··
RLO
ROW
RLO
ROW
RLO
ROW
1991
0-10 cm
1.56a (a)
2.73a (a)
3.32a (a)
3.90a (a)
2.74a (a)
3.23a (a)
2.54a
3.29a
20-30 cm
1.14a(a)
2.20a (a)
1.03b (a)
2.15b (ab)
0.75b (a)
1.58b (b)
0.98b
1.98b
Average· ••
1.35b
2,47ab
2.17a
3.02a
1.74ab
2.40b
1992
0-10 cm
1.93a (b)
2.11a(b)
7.88a (ab)
5.38a (ab)
11 . 18a (a)
6.68a (a)
7.0a
4.72a
20-30cm
2.24a (a)
2.66a (a)
1.20b (aO
1,45b (a)
0.8b (a)
1 .90b (a)
1.42b
2.0b
Average·· •
2.09ab
2.38b
4.35ab
3.41 a
6.19a
4.29a
•
Density expressed in cm/cm3 xl 0.3
••
Dry weight express in 10.2 mg/cm 3
••• Means for tillages have been separated independently from others in columns.
Note: Means within columns with same letter are not significantly different (a = 0.05).
Means within rows in parentheses with same letter are not significantly different (a = 0.05).
RLD = root length density; ROW = root dry weight

Table 3.
Effect of intercropping on plant root growth for year 1991 and 1992.
Root
Growth
Depth
~
~
SG
~
~
_V_
Average
Parameter
1991
RLO+
0-10 cm
4.85a (a)
4.40a (a)
2.49a (b)
0.88a (c)
2.15a (bc)
0.86a (c)
2.54a
20-30 cm
1.61b (a)
1.98b (a)
0.93b (b)
0.39b (c)
0.67b (bc)
0.62a (bc)
0.98b
ROW
0-10 cm
5.40a (a)
5.07a (a)
2.96a (b)
1.96a (b)
2.92a (b)
2.09a (b)
3.89a
20-30 cm
2.78b (a)
3.15b (a)
1.92b (b)
1.16b (c)
'1.61b (bc)
1.64a (bc)
1.98b
RLO
3.23a
3.19a
1.71 b
0.64c
1.41 bc
0.74c
Average
I
ROW
4.09a
4.11 a
2.44b
1.56b
2.27b
1.87b
1992
RLO
0-10 cm
5.57a (bc)
18.03a (a)
4.94a (bc)
1.30a (c)
8.51a (b)
4.17a (bcl
7.0a
20-30 cm
0.91b (ab)
1.80b (a)
1.98b (a)
0.34b (b)
1.46b (ab)
1.41 b (ab)
1.42b
ROW
0-10 cm
5.15a (bl
7.29a (a)
4.01 a (b)
1.74a (c)
5.71a (ab)
4.15a (b)
4.72a
20-30 cm
1.74b (be)
2.86b (a)
2.30b (ab)
0.96b (c)
1.95b (abc)
1.96b (abc)
2.0b
RLO
3.24be
9.92a
3.46be
0.82e
4.99b
2.79bc
Average
RDW
3.44b
5.08a
3.15b
1.35c
3.83ab
3.05b
.. Root density expressed in 10-3 cm/cm3 and root weight expressed in 10-2 mg/cm3•
Note:
Means within column for each item having same letter without parentheses are not significantly different-.
Means within row with same letter in parentheses are not significantly different (d = 0.05).
Overall means for depth and intercrops have been separated independently.
RLO = root length density; ROW = root dry weight

Table 4.
Overall all averages of root length density (RLD). root dry weight (RDW). relative
competition pressure (cP.n). and ratio of RDW to RLD (RDW/RLD) for 1991 and
1992.
1991
1992
RLD·
CP."
RDW··
RDW/RLD
RLD
CPsJi
RDW
RDW/RLD
SF
3.73a
4.09a
1.27
3.24be
3.44b
1.06
S
3.19a
4.11 a
1.30
9.93a
5.08a
0.51
SG
1.71 b
7.86(5)
2.44b
1.43
3.46bc
2.87(51
3.15b
0.91
0.36(G)
0.24(Gl
G
0.64c
1.56b
2.44
0.82c
1.35c
1.65
SV
1.41 be
2.26(5)
2.27b
1.61
4.99b
1.99(5)
3.83b
0.77
0.52(V)
0.56(V)
V
0.74c
1.87b
2.53
2.79be
3.05b
1.09
•
Density expressed in em/cm 3 x1 0.3
••
Dry weight express in 10-2 mg/cm 3
Note: Means within columns with same letter are not significantly different (a = 0.05).
RLD := root length density; RDW := root dry weight
t
I
I
I
I
I

50
8
Plantin,9
1991
7
~~!...
40
!
. .
Harves.t 6
,
..
..~ 5
30~ .•
••
:. :r
4
20t ..
. ; I
;.~V
. { 3 E
I
•
.
•
•....
2 E
10 _. .
• 1
c
..........
0
E
0
~
5 0
~
=
,108-
~801
~o
. '
40
'".
4
20'
2
oI, 11 ,11 1111 ,,' ,I 11 I I" ' , Ih h 11·.0.11,..1', J,
11'
,11111
I .. - ,
!J 11· .... ' , • •
, . . ' "
I",'.'
11,'··,
I ! !
I 0
June
'July
Aug.
Sept.
Oct.
Figure 1: Daily rainfall and pan evaporation during the growing seasons.
Dot lines represent pan evaporation; Bars represent rainfall.
-
- ~-

- - --
5
1991
4
--.. -
3
'""'
cry
E 2
u
-'-~:~-~;~--'~'~-~~-~~~:~'~-:~l:'~:~:~:~:~~,----'---
---E 1
U
cry
I._.~--._._._._._._._._._._.~._._._.----.-.-._-_.-._._.-.-.-._._.~
.. :::.:'::'" - - - - - - - - - - -
~%
~
~
~
~
I
,--
'--'
1
1992
..... --
'5
SE _S,V ii SY SG
.. -------
I
1
; ; 10·
0)
C
_.._..- ..- .._.._..-. _..-'
W
"0 5-,
----
..-..-... "'1'
'f"
.-
_.--
, "
..
._--._.-._-
. . . . . . - : "
o
a:
-..~~..::-~:.=~:~=--=-:"'~':~'='=' -- -----'-'='='='='=-=-=.'
.~-
~o
30
40
50
60
Days after planti ng
Figure 2: Effect of intercropping on plant root growth.
Error bars indicate LSD(O.05).

46
REFERENCES
Arora, VK., P.R. Gajri, and S.S. Prihar. 1991. Tillage effect on corn in
sandy soils in relation to water retentivity, nutrient and water
management, and seasonal evaporativity. Soil & tillage Research. 21 :
1-21.
Blevins, R.L., G.W. Thomas, M.S. Smith, W.W. Frye, and P.L. Cornelius.
1984.
Changes in soil properties after 10 years no-tilled and
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Brady, N. 1974. The nature and properties of soils. Macmillan Publishing
Co., Inc. New York. PP. 639.
Cooper, A.J. 1973. Root temperature and plant growth. Research review
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Slough SL2 3BN, England, 73 pp.
- Doggett, H. 1988. Sorghum. Longman, Scientific and John Willey, New
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Foy, C.D, 1992. Soil chemical factors limiting plant root growth. P. 97-
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Gregory, P.J. 1988. Growth and functioning of plant roots. PP. 115-167.
ill: A. Wild. (Ed) Russell's soil conditions and plant growth. John
Wiley & Son, Inc., New York.
Guertal, E.A., D.J. Eckert, S.J. Traina, and T.J. Logan. 1991.
Differential
phosphorus retention in soil profiles under no-till crop production. Soil
Sci. Soc. Am. J. 55: 410-413.
Gupta, S.C., W.E. Larson, and R.R. Allmaras. 1984. Predicting soil
temperature and soil heat flux under different tillage-surface residue
conditions. Soil Sci. Soc. Am. 48:223-232.
Hammond, L. C., K. J. Boote, R. J. Varnell, and W. K. Robertson. 1980.
Water use and yield of peanuts on a well-drained sandy soli. Proc.
Amer. Peanut Res. & Educ. assoc .. 10:73 Abstr.
Haynes, R.J. and T.L. Knight. 1989. Comparison of soil chemical
properties, enzyme activities, levels of biomass N and aggregate
stability in the soil profile under conventional and no-tillage in
Canterbury, New Zealand. Soil & Tillage Research. 14: 197-208
Hikam, S., C.G. Poleneit, C.T. MacKown and D.F. Hildebrand. 1992.
Intercropping of maize and winged bean. Crop Sci. 32: 195-198.
Hulugalle, N.R., R. Lal, and C.H.Ter Kuile. 1984. Soil physical changes and
crop root growth following different methods of land clearing in
Western Nigeria. Soil Science. 138: 172-179.
Kenneth, J.B., J.R. Stansell, A.M. Schubert, and J.F. Stone.
1982.
Irrigation, water use, and water relations. ill: H. E. Pattee and C. T.

47
Young (eds.) Peanut Science and Technology. American Peanut
Research and Education Society, Inc. P. 164-205.
Klepper, B. 1992. Development and growth of crop root systems. P. 1-25.
!D. Hatfield, J.L. and B.A. Stewart (Ed.) Limitations to plant root
growth. Advances in Soil Science. V.19.
Lai, T.M., and K. Lawton. 1962. Root competition for fertilizer phosphorus
as affected by intercropping. Soil Sci. Soc. Amer. Proc. 26:58-62.
Lal. R. 1975. Role of mulching techniques in tropical soil and residue
management. liTA Tech 'Bulletin 1'.
Lal. R. 1977. Soil conservation and management in tropical Africa. 1.0.: D.J.
Greenland and R.Lal (Ed.) Soil conservation and management in the
humid tropics. Wiley, London. PP. 93-98.
Lenka, D. and P. K. Misra. 1973.
Response of peanut (Arachis ypogaea L.)
to irrigation. Indian J. Agron. 18:492-497.
McCloud, D. E. 1974. Growth analysis of high yielding peanuts (Arachis
apogaea L.). Proc. Soil and Crop Sci. Soc. Fla. 33:24-26.
Meisner, A. A. and K. J. Karnok. 1992.
Peanut root response to drought
stress. Agron. J. 84: 159-165.
Morris, H.D., and W.H. Pierre. 1949. Minimum concentrations of
manganese necessary for injury to various legumes in culture
solutions. Agron. J. 41; 107-112.
Mosher, P.N. and M.H. Miller. 1972. Influence of soil temperature on the
geotropic response of corn roots (Zea mays L.). Agron. J. 64:458-
462.
Monchoge, B.O. and S. M. Mwonga.
1988. The effects of tillage on
organic carbon and other physical and chemical properties of a
semiarid soil in Kenya. PP. 382-384. 1.0.: P.W. Unger, T.V. Sneed and
R.Jensen (Ed.) Challenges in dryland agriculture. A global perspective.
Proceedings of the International Conference on Dryland Farming.
Amarillo/Bushland, Texas, U.S.A.
Ne'Smith, D.S., W.L. Hargrove, D.E. Radcliffe, and'E.W. Tollner. 1984.
Tillage and residue management effects on soil physical properties. P.
87-92. !D.: Hargrove, W.L., F.C. Boswell, and G.W. Langdale (eds)
Proceedings of the 1985 southern region no-till conference. Griffin,
Georgia.
Pandey, R.K., W .A. T. Herrera, A. N. Villegas, and J. W. Pendleton. 1984.
Drought response of grain legumes under irrigation gradient: Ill. Plant
growth.
Agron. J. 76: 557-560.
Payne, D. and P.J. Gregory. 1988. The temperature of the soil. P. 283-
297. !D.: A. Wild. (Edl Russell's soil conditions and plant growth. John
Wiley & Son, Inc., New York.
Prihar, S.S., K.S. Sandhu, M. Singh, H.N. Verma, and R. Singh. 1989.
Response of dryland wheat to small supplemental irrigation and
fertilizer N in submontane Punjab. Fert. Res. 21: 23-28.

48
Reddy, M .S. and R. W. Willey. 1980. The relative importance of above- and
below-ground resource use in determining yield advantages in pearl
millet/peanut intercropping-Summary. P. 70-71. ill: C. L. Keswani and
B.J. Ndunguru (eds.) Intercropping. Proceedings of the Second
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fine sands. Proc. Soil and Crop Sci. Soc. FLA. 38: 54-59.
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Advances in Soil Science. V.19.

CHAPTER 4
EFFECT OF INTERCROPPING AND TILLAGE/RESIDUE
MANAGEMENT ON PLANT COMPETITION FOR WATER.
ABSTRACT
Small-holding farmers in the tropics have traditionally intercropped
their lands under different tillage and residue management practices. Yet,
little quantitative information is available about water use by intercropped
species grown together under varying tillage and residue management
practices. A split plot design was used on a Cecil sandy clay loam soil in
Griffin, Georgia, in summer 1991 and 1992 to study the effect of
intercropping grain sorghum [Sorghum bicolor (L.) Moench,cv. "Pioneer
8230" ] with peanut [Arachis hypogaea L., cv. "Southern Runner"], or
velvet bean [Stizolobium deeringianum Bort, vc. "Early Speckled Velvet
Bean"] in conventional tillage (CT), no-tillage with residue cover (NTC) and
no-tillage bare (NTB) on soil water content.
Soil water content was
measured by time domain reflectrometry (TDR) at 6 depths from 0 to 90 cm
in 15 cm increments during the growing seasons. Greater water content
was observed with NTC compared to CT. The NTB was intermediary but
49

50
significant different from both NTC and CT in 1992.
Rain acceptance
measured by use of a sprinkler infiltrometer showed greater water infiltration
in NTC compared to NTB and CT, explaining the moisture advantage of NTC.
Water infiltration in no-tillage velvet bean monocrop was particularly
improved at the end of the experiment. Intercropping tended to enhance soil
water use compared to sorghum monocrop. There was significant
interaction between intercropping and tillage/residue management systems,
suggesting careful selection of intercrops and soil management systems for
satisfactory crop production. Despite differences between years, most
treatment comparisons were unaHected.
INTRODUCTION
No-tillage and residue mulches are efficient strategies for soil and
water conservation (Okigbo, 1969, Lal, 1975; Russelle and Hargrove,
1989). Crop residue mulches absorb kinetic energy of rain drops, thereby
reducing surface crusting, water runoff and erosion (Lal, 1975; Radcliffe et
aI., 1988; Russelle and Hargrove, 1989; West et ai, 1991). They also
reflect solar radiation, resulting in reduced thermal fluctuations and water
evaporation (Lal, 1975; Harrison and Lal, 1979; Dexter et al., 1982;
Shopart, 1987; NeSmith et al., 1987b).
In addition, the return of crop
resid ue to the soil enhances the soil organic matter content and nutrient
cycling (Okigbo, 1990). Soil organic matter encourages good soil
structuring, which improves soil water properties (Boyle et al., 1989).
Residue cover also serves as refuge and/or food resource for soil dwellers

51
such as earthworms and subterranean insects (Dexter et al., 1982). Soil
invertebrates not only contribute to nutrient cycling, but also are major
pedoturbation agents (Lal, 1987; Lavelle, 1988). They also create macro-
pores and enhance soil aggregation, which improves water infiltration
(Lavelle, 1988; Radcliffe et al., 1988). Hillel (1980) suggested that soil with
high macro-porosity looses less water by evaporation because capillary rise
of water is not favored by large pore sizes.
Consequently, soil invertebrate
activity improves both rain acceptance and water conservation. Because of
its many advantages in improving soil quality, no-tillage cover has often been
mentioned as a component of sustainable agriculture (Russelle and Hargrove,
1989; National research council, 1990). In contrast, conventional tillage
and no-tillage with residue removed, two tillage/residue management
systems of common practice in the United States and in West Africa
respectively, expose the soil surface to the effect of raind rop impact,
resulting in soli crusting and compaction (La!, 1975; Harrison and Lal, 1979;
Phi/lips, 1984; NeSmith et al., 1987a; Lal, 1987; Gajri et al., 1992). This
combines with reduced soil macro-porosity to limit water infiltration in favor
of runoff and erosion.
Regardless of tillage and crop residue management system, most
farmers in Africa have traditionally intercropped their lands to minimize risks
associated with monocultures and to assure stable income and nutrition
levels (Francis et al., 1975).
Advantages associated with intercropping
include; 1) yield security in the event of epidemics, water shortage or
flooding, 2) reduced inter- and intra-crop competition for resources, 3) high
resource use efficiency, 4) yield advantage over monocropping, and 5)
reduced rate of soil nutrient depletion (Huxley and Maingu, 1978; Willey,

52
1979; Ikeorgu and Odurukwe, 1989; Russelle and Hargrove, 1989}.
Plant
competition for resources (light, soil water, nutrients, and carbon dioxide)
occurs during all or part of the growing season (Gomez and Gomez, 1983;
Russelle and Hargrove, 1989), and the productivity of each companion crop
is dependant on its ability to compete.
In general cereal intercrops are favored by their extensive root
systems and are more competit~ve than legumes for below ground resource
acquisition {Lai and Lawton, 1962; Wolfe and Lazenby, 1973; Mays et al.,
1980; Caradus, 1980; Hart, 1981; Wolfe et al., 1982; Pleasant, 1982}.
However, the severity of inter-crop competition depends on a number of -
factors including; 1} soil water and nutrient availability, 2} intercrop planting
density and geometry, 3) timing of planting, 4) intercrop species or varieties
and 5) extent of nitchbreath overlap {Willey et Reddy, 1981; Gomez and
Gomez, 1983; Davis et aI., 1986; Ofori and Stern, 1987; Russelle and
Hargrove, 1989}.
When compatible crops are intercropped, reverse flow of water from
deep rooting species which tap water from deep horizons {Gregory, 1988;
Nobel, 1991} can permit the survival of the shallow rooting companion crops
during drought periods {Hardwood, 1984; Blevins, 1987; Corak et al.,
1987}. This indicates that intercropping can improve water use efficiency
and exhibit yield advantage over monocropping (Reddy and Willey, 1980;
Natarajan and Willey, 1980).
The effects of intercropping, tillage and residue management on crop
performance often have been investigated separately.
In addition, although
there are numerous reports concerning plant competition for water and
nutrients, many crop mixtures remain untested.
The present work was

53
designed to study plant competition for water under conventional tillage, no-
tillage with residue mulch, and no-tillage bare when crops are grown in pure
or mixed stands.
MATERIALS AND METHODS
Experimental design
A field study was conducted in summer 1990 and 1992 on a Cecil-
sandy clay loam at Griffin, Georgia.
Following a long fallow during which
grasses were the predominant vegetation, the soil was planted to potato for
one year, then wheat for 2 years prior to the experiment. In Summer 1990,
wheat residues were removed, and soil was conventionally tilled to 30 cm
soil depth before planting forage sorghum over the entire the area. This was
done to reduce spatial differences and to further depress the soil nutrient
content in order to increase the potential for observing treatment effects.
After harvest in early October 1990, the experiment was laid out as a split-
plot design in randomized complete blocks with 3 replicates.
Main-
treatments, which were immediately applied consisted of conventional tillage
(CT), no-tillage bare (NTB), and no-tillage cover (NTC). Main- treatments
were re-applied about 2 weeks after the 1991 harvest for the 1992
experiment. Subplot treatments, applied at planting, consisted of pure
stands of grain sorghum [Sorghum bicolor (L.) Moench,cv. "Pioneer 8230"]
fertilized (SF) and unfertilized (S), peanut [Arachis hypogaea L., cv.
"Southern Runner"} (G), velvet bean [Stizolobium deeringianum Bort, vc.

54
"Early Speckled Velvet Bean] (Vl. and mixed stands of sorghum/peanut (SG),
and sorghum/velvet bean (SV).
Grain sorghum and peanut were used 1)
because of they are important as food and/or cash crops, and 2) because
their are often intercropped in tropical Africa.
Velvet bean was used
because of its potential for fixing nitrogen and producing heavy biomass for
soil improvement (Scott, 1946;
Burle et al., 1992). This crop was once
popular in Georgia for use as green manure (USDA, 1957; Scott, 1946). Its
use declined with decreased cost of inorganic fertilizers.
Returning to the
use of velvet bean for soil improvement can foster agricultural sustainability.
NPK fertilizer (90 kg N, 45 kg P 0
and 67 kg K 0 per hectare) was hana
2
5
2
broadcasted in SF treatment about 20 days after emergence. Crops in
mixtures were planted in alternate double rows.
Each subplot consisted of 8
rows, 75 cm apart and 12 m long. Plants were about 10 cm apart within
row: Plant populations for all crops averaged 200,000 and 100,000 plants
per hectare in pure and mixed stands, respectively. Weeds were controlled
as needed during growing season by hoeing and during winter period by
application of 0.56 kg/ha paraquat (1,1' dimethyl-4,4'-bibyridiniumion).
Crops were planted and harvested on June 1 and October 28 in 1991, and
on June 15 and October 16 in 1992, respectively. A reduced rainfall was
observed during the 1992 growing season, compared to 1991 (Chapter 3).
For these reasons, crops were disadvantaged in 1992 compared to 1991.
Measurement of rain acceptance
Rain acceptance was measured during the period of 10 to 21 May
1991 and 1992, and 14 to 18 January 1993, respectively 7 and 2 months

55
after tillage/residue management treatments were applied. During the time
interval between main treatment application and infiltration measurement
several rains events were recorded. In 1993, infiltration measurements
followed 22 rains, the largest averaging 43 mm.
All measurements were
made using a sprinkler infiltrometer (Petersons and Bubenzer, 1986). Rain
was simulated over a squared metal enclosure of 0.92 m width for 45
minutes at sprinkler rates of 60, 68 and 63 mmh- 1 in 1991, 1992 and 1993
respectively. Pounding water was pumped off and the amount recorded
every alternate minutes.
Enclosure was randomly positioned on a middle
row so that it straddles-the row.
Because nontraffic and traffic inter-rows
were alternate, this arrangement allowed both effects to be equally
accounted for in the runoff measurements (Radcliffe et al., 1988). Care was
taken not to disturb the soil within the enclosure. However, soil was
carefully packed against the enclosure inside and outside to avoid
preferential side "flow along the wall.
In all years, measurements concerned
only sorghum and velvet bean monocropped plots in NTC and sorghum
monocropped plots in NTB and NTC.
Surface cover by forage sorghum residue averaged 27% in April 1991
in NTC.
Soil cover by velvet bean and sorghum residues averaged 100%
and 48 % in 1992, and 100% and 63 % in 1993, respectively at the time of
rainfall simulation.
Residue removal reduced soil cover to less than 12% in
the NTB each year. The incorporation of crop residues in CT resulted in zero
soil coverage.

56
Soil moisture measurement.
Soil water content was measured 6 and 8 times during the 1991 and
1992 growing seasons, respectively, from seedling to crop maturity by time-
domain reflectrometry (TOR) using a cable tester (Tektronix Inc., Beaverton,
Oregon, USA).
Measurements were done on relatively dry days where
differences among treatments were more likely to be observed.
Measurements were done in all main plots and subplots at 6 depths from 0
to 90 cm in 15 cm increments. Six pairs of solid stainless steel welding
rods, 0.39 cm diameter,-were vertically driven into the soil half-way
between rows in the center of the plot, in a single line of increasing depth,
and used as transmission lines (Topp and Oavis, 1985). Rods in intercrop
treatments were installed half-way between rows of intercrops. Rods of
each pair were of equal length and were placed 5 cm apart and pairs about
15 cm apart.
TOR readings were converted to soli volumetric water content
using the following calibration equation (Mulla, 1989):
e = - 0.053 + 2.92 x 10-2 K - 5.5 X 10-4 K2 + 4.3 X 10-6 K3,
where K = (TOR reading/rod length)2.
Because vertical rods measure the average water content over their
entire length, length weighted averages of the measured water contents
were computed to match the 15 cm depth increments. All data were
statistically analyzed by year, date of sampling, tillage/residue management
system, crop treatment, and depth using the statistical analysis system
(SAS) (SAS Institute, Inc.).

57
RESULTS AND DISCUSSION
General rainfall and soil profile moisture distribution.
Annual rainfall was 1126 and 1479 • mm for 1991 and 1992
respectively, indicating a 31 % difference between the two years. However,
daily rainfall distribution presented in Figure 1, Chapter 3, for both growing
seasons show that crops were advantaged in 1991 compared to 1992. A
late season drought was observed in 1991 in September, while an early
water shortage was recorded in 1992, from mid June to mid July. Crops
were planted on June 1 and on June 15 in 1991 and 1992 respectively.
Average moisture distribution over all treatments in the soil profile for both
growing seasons is presented in Figure 1. Soil water content increased with
soil depth. Mean separation among depths within main treatments was
consistent in 1991 and 1992 (Table 1) showing that moisture distribution
from 0 to 60 cm depths was not affected by seasonal differences in rainfall.
Effect of tillage/residue management on water infiltration
The effect of tillage/residue management on rain acceptance is shown
in Figure 2 for all years.
Visual observation during the experiment indicated
that earthworm population was greatly enhanced by residue cover in NTC,
especially under the velvet bean residues. This may have enhanced the soil
macro-porosity which added to the surface cover to increase water
infiltration in I\\JTC. Water infiltration in the NTC-velvet bean monocrop was
significantly greater than that observed in the NTB and CT. Reasons for

58
reduced water infiltration in NTB and CT may include:
1) increased soil
crusting and 2) reduced macro-porosity, both resulting from reduced surface
cover. The greater water infiltration rate tended to be greater in the NTB
than in the CT, corroborateing a report by We ss et al., 1991. This may be
attributable to the presence of stubbles, root channels, and preserved soil
aggregate stability in the NTB.
However, no measurement of soil aggregate
stability or root channel effect was made to substantiate the above
assumption. Another factor, soil gravimetric water content in the top 7.5
cm soil depth averaged 22-28.5% under I'HC-velvet bean compared to 9-
11 % in CT and 9.5-10-.5% in NTB during early and late 1992 infiltration
measurement, respectively.
Initially dry soil conditions in NTB and CT may
have favored slaking-crusting, compounding early and greater runoff
compared to NTC.
Effect of tillage/residue management on soil moisture content
Temporal change in soil moisture content in the first 15 cm of soil
under the different tillageJresid ue management systems is presented in
Figure 3 for both years. Greater water infiltration rate (Figure 2) added to
the residue cover to provide NTC with soil moisture advantage over NTB and
CT.
In general, differences between CT and NTC were significant in both
years and at all depths above 60 cm except at 45 cm depth (Table 1).
NeSmith et al. (1987) reported similar ranking of these treatments for
moisture content. Likewise, soil water content in NTB and CT corroborates
the rain acceptance measurements, confirming several previous reports (Lal,
1975; Dexter et al., 1982; Radcliffe et al., 1988; Miller and Radcliffe,

59
1992). There was no significant difference between NTC and NTB in 1991
as a result of lack of treatment effect.
However, NTB became significantly
drier than NTC in 1992 probably due to changes in soil properties.
Effect of intercropping on soil moisture content.
Temporal changes in the average soil water content within the first 60
cm soil depth under pure stands of unfertilized sorghum, peanut and velvet
bean are presented in Figure 4 for 1991 and 1992.
Behavior of these crops
at individual depths for 1991 is shown in Figures 5-8.
Within the top- 60 cm
depth, ranking of these treatments for soil water content was V < S < G
(Figures 4, 5 and 7). Sorghum soil water content tended to be the lowest
below 60 cm (Figures 6 and 8), confirming its deep rooting habit (Rachie and
Majmudar, 1980; Doggett, 1988).
The effect of intercropping sorghum with peanut (SG) or velvet bean
(SV) on soil water content in the 0-60 cm depth compared to monocrop
sorghum (5) is shown for 1991 and 1992 in Figures 9 and 10, respectively.
With the exception of CT in 1991 and NTB in 1992, intercropping resulted
in reduced soil water content compared to sorghum monocropping,
suggesting a more thorough soil exploration and soil water use by in the
intercrops than in the sorghum monocrop. Crop treatment comparison at
depth 45-60 cm in 1992 (Table 2) shows a significantly reduced soil water
content in both mixtures compared to the pure stands of sorghum and
peanut. This finding seems to indicate that the intercrop competition was
greater at this depth and suggests a good knowledge of the soil profile
water distribution to guide the decision for crop association. The

60
observation of Table 3 and Figures 9 and 10 shows that the comparison
among crop treatments was affected by the main treatments, indicating a
significant interaction between intercropping and tillagelresidue management
practice. This sugests a careful selection of intercrops and soil management
systems for satisfactory crop production.
CONCLUSION
These results-clearly confirmed the differences among the
tillage/residue management systems tested.
Residue
"
removal) and probably
an improved soil macro-porosity favored water infiltration and conservation,
resulting in greater water content in NTC compared to NTB and CT. The
least water infiltration rate and soil water content were observed in the CT.
Reduced soil water content in the mixtures suggested a better soil
exploration and more thorough use of soil water by the intercrops as
compared to sorghum monocrop. Increased competition for water between
sorghum and either legume appeared to occur at 45-60 cm soil depth.
There was significant interaction between intercropping and tillage/residue
management systems, suggesting careful selection of intercrops and soil
management systems for satisfactory crop production. Despite differences
between years, most treatment comparisons were unaffected.

Table 1. Soil profile moisture (%) status under different crop residue management systems
for year 1991 and 1992.
Depth #
Soil Depth
eT
NTC
NTB
Mean
Year 1991
1
o - 15
13.54e (b)
17 .14d (a)
17.53d(al
16.07e
2
15 - 30
16.11 d (b)
20.99c (a)
19.27d (a)
18.79d
3
30 - 45
25.91b (a)
26.46b (a)
26.07bc (a)
26.15c
4
45 - 60
23.09c (b)
30.56a (a)
24.92c (ab)
26.19c
5
60 - 75
28.37ab (ab) 31.13alal
28.14b (b)
29.21b
6
75 - 90
30.31 a (a)
31.71a (a)
35.10a (a)
32.27a
Mean
22.89b
26.33a
25.17a
Year 1992
1
0-15
13.93f (b)
16.91f (a)
1694d (a)
15.93d
2
15-30
18.23e (c)
22.94e (a)
20.83c (b)
20.67c
3
30-45
25.92c (a)
25.35d (a)
25.06b (a)
25.44b
4
45-60
22.56d (b)
27.10c (a)
25.21b (ab)
24.96b
5
60-75
32.32b (a)
36.79a (a)
33.38a (al
34.16a
6
75-90
34.87a (a)
34.18b (a)
32.88a (a)
33.98a
Mean
24.64b
27.21a
25. nab
Note:
Means within columns, for each year, with same letter without parentheses are not
significantly different (a = 0.05).
Means within rows, for each year, with same letter in parentheses are not significantly
different (a = 0.05).

Table 2. Effect of intercropping on soil moisture depletion for year 1991 and 1992.
Depth
SF
S
SG
G
SV
V
Year 1991
0-15
16.24c (a)
16.55c (al
16.39d (a)
13.54e (bl
16.39d (e)
15.32c (ab)
15-30
17.97c(b)
19.08e (ab)
19.97e (a)
16.11d(bl
19.36e (a)
17.13e (b)
30-45
26.56b (ab)
25.31 b (ab)
27.12ab (ab)
25.91 b (ab)
27.44b (a)
24.40b (b)
45-60
25.91b (b)
25.91b (be)
29.46a (a)
23.0ge (c)
24.65b (be) 24.17b (be)
60-75
26.07b (cd) 28.35b (bel
25.11b(d)
28.37ab (bel
33.60a (a)
30.16a (be)
75-90
33.29a (abL 34.39a (ab)
28.84a (b)
30.31 a (ab)
30.85a (abl 35.61 a (a)
Average 24.34b
24.60ab
24.48ab
25.69a
25.38ab
24.48ab
Year 1992
0-15
16.39d la)
16.52d (a)
1 5.97d (a)
15.2ge (a)
1525d (a)
16.13d (a)
15-30
20.21e (ab) 21.64e(a)
20.35c (ab)
20.96d (ab)
21 .13e (ab)
19.68e (b)
30-45
24.24b (b)
25.32b (ab)
25.90b (ab)
26.94e (a)
25.60b (ab) 24.65b (b)
45-60
25.34b (abl 26.93b (a)
23.68b (b)
26.48e (ab)
23.74be (b) 23.56b (b)
60-75
32.08a (b)
32.67a (b)
32.30a (b)
39.40a (a)
33.82a (b)
34.70a (b)
75-90
33.71a (a)
35.25a (a)
34.33a (a)
34.45b (a)
32 29a (a)
33.83a (a)
Average 25.33b
26.39ab
25.42b
27.25a
2531 b
25.43b
Note:
Means within column for each year with same letter without parentheses are not
significantly different (a = 0.05).
Means within row, for each year, with same letter in parentheses are not significantly
different (a = 0.05).

Table 3. Effect of intercropping and crop residue management systems on soil moisture
content for year 1991 and 1992.
Crop Treatment
CT
NTC
NTB
Average
Year 1991
SF
24.89a (a)
25.15a (a)
22.98a (a)
24.34b
S
19.87c (cl
28.88a (al
25.94a (bl
24.60ab
SG
24.10a (a)
24.43a (a)
24.86a(al
24.48a
G
23.75a (bl
26.60a (al
26.73a (al
25.69a
SV
24.27a (b)
26.67a (a)
25.20a (ab)
25.38a
V
22.63b (bl
25.90a (a)
24.85a (a)
24.46b
Mean
23.25b
26.27a
25.09a
Year 1992
SF
24.63ab (a)
26.49a (a)
24.86a (a)
25.33
S
25.43ab (b)
29.18a (a)
24.56a (bl
26.39
SG
24.91ab (a)
25.01 a (a)
26.34a (a)
25.42
G
26.16a (a)
27.71a (a)
27.89a (a)
27.25
SV
23.21 b (c)
27.62a (a)
25.10a (b)
25.31
V
23.4 7b (b)
27.26a (a)
25.55a (a)
25.43
Average
24.64c
27.21a
25.72b
Note:
Means within column, for each year, with same letter without parentheses are not
significantly different (a = 0.05).
Means within row, for each year, with same letter in parentheses are not significantly
different (a = 0.05).

201-
'~
I
1992
1
1991 !
- - - --
- -~
40 1-
E
()
c
..c
+-'
0-
m
60 -
r
l:J
0
Cl)
80'-
100'
t
I
!
15
20
25
30
35
Soil water content (%)
Figure 1: Average seasonal soil profile water content over
all treatments ih 1991 and 1992.

100
,,,,,
May 1991
80
,,
Sprinkler rate: 60 mm/hr
,,
NTB ",
60
,
eT .....
'.
40
.......
..--..
......
_
.
............... ~
cf!-
1Smm!hr
- 2 0
.....
ID
7mm/hr
CO
"-
00
10
20
30
40
50
C
.0 100
May 1992
January 1992
~.
.\\
\\
CO
Sprinkler rate: 68 mm/hr
,\\
Sprinkler rate: 63 mm/hr
'.
\\ \\
"-
+-J
......,\\"-. \\
80
,\\
'.
\\: \\
S1 mm/hr
'+=
,\\
C
NTC-V
\\\\
'-\\.......
-
60
\\\\ .'''.
\\
....( \\
"
"
....... ',
. \\ / \\ ' - ,
~
.
....
35mm/hr*
. . . . . . . . "
21 mm/hr NTC-S
40
'~"v" - "'.
'.
~ ......
"
.,' ..
".~::~. ~"'.
"
,
-
"
~
. ,
.... \\..('""'-:..
12mm/hr
..-.......
- -
............ - /
NTB-S
.....
' \\ " . - - -
............ ':~.:.- .. _
- ..-:::- ..~ ..~ .. ~ ....~.
CT-S
20
••••••• . ' . . _ •• ;00 •• ,
•• -
4.7mrTi/hr
2'm~iiir'
00
10
20
30
40
50 0
10
i
20
30
40
50
Time (minutes)
Fugure 2: Infiltration rate with time.
NTC-V = No-till velvet bean cover; NTC-S = No-till sorghum cover
NTB-S = No-till sorghum bare; CT-S = Conventional tillage sorghum
it
Final infiltration rate is presented for NTC-V, NTC- Sand CT-S

35
, .\\
30
\\
1991
' \\
....' \\
'. \\
25
'. \\
'. \\'. \\'.\\
20
'. \\".\\.\\
15
....:--".._
J-----
' ..' ~.......
- - - - - -
NTC
~>-'--.lc<:
· : · : : : 1 ~tB
~ 10
+-'
c
Q)
+-'
c
5
0
20
40
60
80
100
120
140
u
25
Q)
"-
:J
+-'
,------"'"t".
en
1992
'0
:T ....
20
~
...... ·I .. ',.
, .
.
"
,
:
I
'.
,
E
-_ ...... - .. _---- ..
, ..
, ..
, .'
'0
, ..
, ..
if)
, ..
15
, ..
10
.
~.. NTC
NTB
CT
~IO
40
60
80
100
120
Days after planting
Figure 3: Effect of tillage/residue management practices on soil water content
in the top 15 cm soil depth. Error bars indicate LSD(O.05).

32i~
30
--r===:~~-
1991
28
26
.........
cfi 24
-...-
C 22
2 20
C
8 1~~
.ID
60
80
100
1~W
1~0
Q)
L....
30.
.
::J
.....
Cl)
1992
-
28
o
--------.
;7--..' .
E
... ///
<..... ...</-:>7~::<
26
I..~·::_·.-:,:r.._.._.._.." --' /.:"
" --'::'-'..,
o
..................':'::..... "
- /;
"" ........
.. ::,,~
Cl) 24
.,
" r
22 ,.
~
40
60
80
100
120
Days after planting
Figure 4: Effect of crop treatments on soil water content within the 0-60 cm
depth during the growmg season. Error bars indicate LSD(O.05).

30
30
0-15 cm
15-30 cm
25
25
20
20
15
15
-*-
"
....
,
c: 10
10
<1>
-c:0u
,
~ S G V
-
.........
I
<1>
~O 40 60 80 100 120 140 ~O 40 60 80 100 120 140
~
:::J
-
.~
0
30 -
E 30
30-45 cm
45-60 cm
·0
Cl)
25
25
20
20
·····l.··
15
15
10
10
~O 40 60 80 100 120 140 ~O 40 60 80 100 120 140
Days after planting
Figure 5: Effect of crop treatment soil water content
at different soil depth during 1991 growing season.
Error bars indicate LSD(O.05).

30
T
I ~ _~_V I
60-75 cm
,
I ' ...
" .
25
---
.......~ .~.-' ~.~ .-..-..~.~.~.~'~'~ ~ - -~'"'"'~'';''; '.
~
' - ' "
+-'
20
C
<D
+-'
C
20
40
60
eo
100
120
140
0
()
<D
' -
:::J
+-'
.~
0
30-
75-90 cm
E
"'.- .. -
0
..... -...
T
T
.....
Cl)
25
.
.
20
20
40
60
eo
100
120
140
Days after planting
Figure 6: Effect of crop treatments on soil moisture content at different
soil depths during 1991 growing season. Error bars indicate LSD(O.05).

30
25
20
15·
..........
~
10
0
'-""
1
0-15 cm
15-30 cm
~
c
Q)
50
40
80
120
~
o
40
80
120
c
0
()
Q)
30
L.
::J
T
~/:-"' __
en 25'-
0
~,T/~"""
E 20
·····1··
~ 15
101-
30-45 cm
45-60 cm
50
40-
80
120
o
40
80
120
Days after planting
Figure 7: Effect of crop treatments on soil moisture content under different
soil depths during the 1992 growing season. Error bars indicate LSD(O.05).

50,
I
k...~~:::.:::.:::1-------6
40
60-75 cm
-
--
T
~":
=
::
:::.:::.~ -1
30
20
---.
*-
I ~ _G__ Y I
-
10
.....
c
Q)
.....
0
40
80
120
C
0
(J
50
Q)
....
175-90 cm
.3 40
(J)
0
E
....:....1"'7'7 ••-;T'.-..~..:.:-•• ~.~ ....••
30
0
Cl)
20
10
o
40
80
120
Days after planting
Figure 8: Effect of crop teatment on soil moisture content at different
sOil depths during 1992 growing season. Error bars indicate LSD(O.05).

32
S
SG
SV
CT
28
l;;~>~..~~.....~...~..,......,.....~.... .·.cc·.·~.·.·cc~"
24
.,..c.....c.
......
-:
20
--
1~0
40
60
80
100
120
140
; . - . - - - - - - - - - - - - - - - ' - - - - - - - ,
--- 32
rfl.
NTC
-...c~§ 28
(J
Q)
~
:J
...
-"-"
.!!! 24
o
.~
-
E
'0
Cl)
20'--0----'------'----------'-------'--------'----'
~
40
60
80
100
120
140
.-:------=---_-----..:._-------_--=....:_----,
32
NTB
28
,
T
........'
l
24
". '. ' - . - - •....\\. . . . . :??4'_"_':':":"':~
2020
40
60
80
100
120
140
Days after planting
Figure 9: Temporal changes in soil moisture content in
the first 60 cm soil depth during 1991 growing season.
Error bars indicate LSD(0.05).

32
S
SG
SV
CT
28
-:-
24
......._.._..
, _._.._..- .._.._..
2020
40
60
80
100
120
- ,...---------------------,
?fl
' - 32
NTC
-CID
-C
/'"
I :
o 28
. . . . .
'::.,;"...1" ............
-.
T / ....
U
-I'-";:"-"-"-<:-..
I :
......
ID
..
.
-
".
-
".
"-
"
...... ......
~
".
" , I
:::J
t)
24
I.:'::'
o
...!...
..
E
'-
o 2020
40
60
80
100
120
Cl)
. - - - - - - - - - - - - - - - - - - - - - - - - ,
32
NTB
28
~-)1:·· ·_ ..:.,.;..
./
...•:.: ",
./
......
24
./
2Cko
40
60
80
100
120
Days after planting
Figure 10: Temporal changes in soil moisture content in
the first 60 cm soil depth during 1992 growing season.
Error bars indicate LSD(0.05).

74
REFERENCES
Blevins, D.G. 1987. Future development in plant nutrition research. 1.0:
L.L. Boersma (ed.) Future development in soil science research.
Soil Sci. Soc. Am., Madison, WI. PP. 445-458.
Boyle, M., W.T. Frankenberger, Jr., and L.H. Stolzy. 1989. The
influence of organic matter on soil aggregation and water
infiltration. J. Prod. Agric. 2:290-299.
Burle, M.L., A.R. Suchet, J.Pereira, D. V. S. Resk, J.R.R. Peres, M.S.
Cravo, W. Bowen, D.R. Bouldin, and D.J. Lathwell.
1992.
legume green manures. Dry season survival and the effect on
succeeding maize crops. Soil Management CRSP Bulletin
Number 92-04. PP. 34.
Caradus, J.R. 1980. Distinguishing between grass and legume species
for efficienc-y of phosphorus use. New Zealand. J. Agr. Res~
23:75-81.
Corack, S.J., D.G. Blevins, and S.G. Pallardy. 1987. Water transfer in
an alfalfa/maize association: Survival of maize during drought.
Plant physio!. 84:582-586.
Davis, J.H.C., J.N. Woolley, and R.A. Moreno. 1986. Multiple
cropping with legumes and starchy roots. pp. 133-160.1.0:
Francis, C.A. (ed.) Multiple cropping systems Macmillan
Publishing Company. New York.
Dexter, A.R., D. Hein, and J.S. Hewitt. 1982. Macro-structure of the
surface layer of a self-mulching clay in relation to cereal
stumble management. Soil Tillage Res. 2: 251-264.
Doggett, H. 1988. Sorghum. Longman, Scientific and John Willey,
New York.
Francis, C.A., C.A. Plor, and S.R. Temple. 1975.
Adapting varieties
for intercropped systems in the tropics. Multiple cropping
symposium, ASA, annual meeting, Knoxville, Tennessee.
Gajri, P.R., V.K. Arora, and S.S Prihar. 1992. Tillage management for
efficient water and nitrogen use in wheat following rice. Soil &
Tillage Research. 24:167-182.
Gomez, A.A. and K.A. Gomez. 1983. Multiple cropping in the humid
tropics of Asia. IDRC. Ottawa. Onto Canada.
Gregory, P.J. 1988. Growth and functioning of plant roots. PP. 115-
167. !.o.: A. Wild. (Ed) Russell's soil conditions and plant
growth. John Wiley & Son, Inc., New York.
Harrison, M.R., and R. La!. 1979. Response of crops to soil
temperature changes. P. 285-304. ill: Lal, R. and D.J. Greenland
(Ed.) Soil physical properties and crop production in the tropics.
J. Wiley & Sons, U.K.

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Hart, A.L. 1981. Analysis of the response of pasture legumes to
phosphorus in a controlled environment. New Zealand. J. Agric.
Res. 24:197-201.
Harwood, R.R. 1984. Organic farming at the Rodale Research Center.
Amer. Soc. Agron. Spec. Publ. 46, pp. 1-17.
Hillel, D. 1980.
Fundamentals of Soil Physics. Academic Press, INC.
PP. 413.
Huxley, P.A. and Z. Maingu. 1978. Use of a systematic spacing
design as an aid to the study of intercropping: some general
considerations. Exp. Agric. 14:49-56.
Ikeorgu, J.E.G. and S.O. Odurukwe. 1989. Increasing the productivity
of cassava/maize intercrops with peanut (Arachis hypogaea L.).
Trop. Agric. (Trinidad) 67, 164-168.
Lai, T.M., and K. Lawton. 1962. Root competition for fertilizer
phosphorus as affected by intercropping. Soil Sci. Soc. Amer.
Pro'c. 26:5.8-62.
Lal. R. 1975. Role of mulching techniques in tropical soil and residue
management. IITA Tech 'Bulletin 1'.
Lal, R. 1987. Earthworms. l..o: Tropical Ecology and Physical
Edaphology. Wiley, New York.
Levelle, P. 1988.
Earthworms and the soil system. Bioi. Fertil. Soils,
6:237-251.
Mays, D.A., S.R. Wilkinson, and C.V. Cole. 1980. Phosphorus
nutrition of forages. P. 805-846. l..o: F.E. Khasawneh, E.C.
Sample., and E.J. Kamprath (eds.) The role of phosphorus in
Agriculture. Am. Soc. Agron. Madison, WI.
Miller, W.P. and D.E. Radcliffe. 1992. Soil crusting in the
Southeastern United States. In: M.E. Sumner and B.A. Stewart
leds.}. Soil Crusting. Chemical and physical processes.
Advances in Soil Science. PP. 179-204.
Morin, J., R. Keren, Y.'Benjamini, M. Ben-Hur, and I. Shainberg.
1989.
Water infiltration as affected by soil crust and moisture
profile. Soil Science. -j 48: 53-59.
Mulla, D.J.
1989.
Measurement and characterization of soil-water
relationships. l..o: T. Gaillard, V. Sadhana (eds.). Soil, Crop,
and Water Management Systems for Rainfed Agriculture in the
Sudano-Sahelian zone. PP. 75-83.
Natarajan, M. and R.W.Willey. 1980. Effects of moisture availability
on intercropping and yield advantages-Summary. P. 71- 7 2. l..o:
C.L. Keswani and B.J.Ndunguru (eds.l Intercropping.
Proceedings of the Second Symposium on Intercropping in
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Academy Press, Washington, D.C. PP. 448

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Nobel, P.S. 1991. Physicochemical and Environmental plant
physiology. Academic Press Inc. London. PP. 635.
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component crops in a maize/cowpea intercrop system. Expl.
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Proceedings of the Second Symposium on Intercropping in
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77
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A field technique for
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92-95. Annual report of plant breeding institute, 1981. Plant
breeding Institute, Cambridge, United Kingdom.

CHAPTER 5
EFFECT OF INTERCROPPING AND TILLAGE/RESIDUE
MANAGEMENT ON PLANT BIOMASS PRODUCTION,
NUTRIENT UPTAKE AND GRAIN YIELD.
ABSTRACT
Intercropping is a traditional crop production method in the tropics.
Yield from intercropping practices are affected by inter-species competition
for water and nutrients. The availability of water and nutrients, in turn, is
affected by tillage and crop tillage/residue management practices. To study
the effect of intercropping and residue management practices on plant
nutrient biomass and yield production, and on the soil chemical properties,
an experiment was conducted on a Cecil sandy clay loam in Griffin, Georgia
during the summers of 1991 and 1992 Llsing a split plot design in
randomized complete blocks. Grain sorghum [Sorghum bicolor (L.) Moench,
cv. "Pioneer 8230" J was intercropped with peanut [Arachis hypogaea L.,
cv. "Southern Runner"], or velvet bean [Stizolobium deeringianum Bort, vc.
"Early Speckled "J under three tillage/residue management practices:
conventional tillage (CT), no-tillage with residue cover (NTC) and no-tillage
bare (NTB).
78

79
In general, plant biomass production, nutrient uptake and grain yield
drastically decreased in the second year of the experiment as a result of
unfavorable rainfall distribution, late planting and reduced soil nutrient
content. On the average, CT favored plant biomass production, nutrient
uptake and yield in 1991 where rainfall distribution was satisfactory. NTC
was advantageous under the drier conditions in 1992 due to its moisture
advantage. Velvet bean yielded significantly more biomass and nitrogen
than sorghum and peanut showing promise for improving soil properties.
The amount of biomass and nutrient uptake in the intercropping systems
was intermediary between the corresponding sole crops. In general,
intercropping improved the residue quality and provided an overall yield
advantage over monocultures. Interaction between intercropping and
tillagelresidue management was generally significant and complex. Changes
in soil nutrient content and pH in NTB suggested that resid ue removal may
lead to a long-term soil infertility.
INTRODUCTION
Intercropping or the simultaneous growing of different crops at
proximate stands, is an efficient crop production strategy with potential for
enhancing agricultural sustainability (Francis, 1986).
When associated crops
are compatible, intercropping can reduce niche-breath overlaps, minimizing
plant competition and improving resource utilization and yield (Gomez and
Gomez, 1983; Davis et al., 1986; Sanders, 1989; Ikeorgu and Odurukwe,
1989; Russelle and Hargrove, 1989; Okigbo, 1990). Numerous factors

80
control inter-crop competition and these factors interact dynamically, making
it difficult to predict the performance of untested mixtures in varying field
conditions (Gliessman, 1986; Trenbath, 1986; Russelle and Hargrove,
1989).
Among these factors, below ground resources availability is
particularly important, increasing inter-plant competition as these resources
become limiting (Willey and Reddy, 1981; Gliessman, 1986; Izauralde et al.,
1990). The availability of below ground resources is highly influenced by
tillage and residue management practices (Phillips, 19884; Blevins et al.,
1984; Haynes and Knight, 1989). In many parts of the tropics where
intercropping is widely practiced, inadequate tillage and residue management
practices often result in reduced yield and rapid soil degradation. Improving
tillage and residue management practices therefore, can further enhance
agricultural sustainability especially if adequate intercropping systems such
as cereal/legume rT,ixtures are used. Although cereal/legume crop
associations often result in a yield depression of the component intercrops
compared to the monocrops, with a greater effect on the legumes (Nyambo
et al., 1980; Davis et al., 1986; Reddy et al., 1988; Izaurralde et al., 1990j,
especially peanut (Koli, 1975; IRAT, 1978; Ikeorgu and Odurukwe, 1989),
many cereal/legume intercropping systems show an overall yield advantage
compared to the monocultures (Sanchez, 1976; Fisher, 1977; Nyambo et
al., 1980; Ikeorgu and Odurukwe, 1989).
Nyambo et al. (1980) reported a
60% increase in the total intercropping productivity over monocropping. In
Senegal, sorghum/peanut intercropping provided an overall yield advantage
compared to the monocultures (Schilling, 1965). Yield advantage of
intercropping systems depends on the nature of competition among plants,

81
which in turn, depends on the resource availability, the cropping strategy,
and the nature of the crops associated (Barker and Francis, 1986).
Nodulated legumes can symbiotically fix a substantial amount of
atmospheric nitrogen (McGuire et al., 1989; Gibson et al., 1977), especially
on soils with reduced nitrogen content (Elowad and Hall, 1987). For
instance, soybean and cowpea derived 33% of their nitrogen from fixation
(Sisworo et al., 1990). Suwanarit et al. (1986) reported that 55-66% of
plant nitrogen was fixed by peanut and soybean. A portion of this fixed N
eventually becomes available to companion cereals, enhancing their dry
matter production and grain yield (Russelle and Hargrove, 1989; Fyson and
Oaks, 1990; Hargrove, W. L. 1986). An important source of N transfer to
non-legumes in mixtures may be through the mineralization of sloughed-off
and dead nodules (Walker et al., 1954). Agboola and Fayemi (1972) also
suggested that excess nitrogen also may be excreted by legume roots in
favor of cereal intercrops. Heichel and Henjum (1991) reported that 36% of
grass N was transferred from intercropped legumes. Izaurralde et al. (1990)
reported greater grain and straw N content in barley intercropped with field
pea than in pure stands.
Greater amounts of legume nitrogen can be
recovered by cereals when intercrop positions are rotated the subsequent
season (Sinnadurai, 1980; Power, 1987; Hargrove, 1986; Burle et al.,
1992).
The percentage of N recovered by non-legume crops generally
depends on two major factors: 1) the rate of N mineralization which in turn,
depends on a} the soil moisture and temperature status (Nyhan, 1976; Stott
et al., 1986; Voroney et al., 1989), b) the quality of the residue (lignin and
N content, C/N ratio) (Smith and Douglas, 1968; Reinertsen et al., 1984;

82
Berendse, 1987) and c) the placement of the residue (Parker, 1962;
Frankenberger and Abdelmagid, 1985), and 2) the N-use efficiency (NUE)
from legumes (NUEl) of the cereal species grown on the legume soil or
intercropped with a legume (Sisworo et al., 1990). The NUEL is typically far
lower than the NUE from fertilizers (NUEF) because fertilizer N is more
readily available than legume-N for plant uptake. As a result, short term
measurements of NUE tend to discourage the use of legumes as a reliable N
source in favor of chemical fertilizers (Bezdicek and Granastein, 1989;
Meisinger , 1984). For example, it has been shown that only 10 to 30% of
legume-N was recovered by the following crop (Lada and Amato, 1986;
Harrison and Hesterman, 1987), compared to recoveries from fertilizer N of
30 to 70% (Stanford, 1987). This prompted Bezdicek and Granatstein
(1990) to recommend that the two N sources should be evaluated over an
extended period to develop a complete N budget of inputs (N fertilizer, N2
fixation, or N deposition), and outputs (harvest, leaching, volatilization,
denitrification).
Meisinger (1984) also proposed that the changes in N pool
sizes (e.g., organic matter, microbial biomass, inorganic N, etc.) be
considered when comparing NUE between legumes and fertilizers.
Taking
into account changes in soil N that take place when legumes are used for
many years, could drastically increase estimates of NUEL, and encourage
the adoption of legume N sources for crop production. Interplanting legumes
with cereals in particular, may not only improve NUEL, but also forestall soil
nutrient depletion and contribute to sustainable crop production.
The changes in soil N discussed above are often influenced by tillqge
and crop residue management practices. In general, these changes are
greater when residues are incorporated as in eT than when residues are

83
maintained on the soil surface as in NTC. This is due to differences in soil
water and physical properties (Hargrove, 1986; Costa et al., 1990).
Differences in soil properties among tillage and residue management systems
may not only affect the NUEL, but also the intercrop competition for
nitrogen. The present work was designed to determine the effect of
intercropping grain sorghum with peanut or velvet bean under conventional
tillage, no-tillage with residue mulch and no-tillage with residue removed on
plant nutrient uptake, dry matter and yield production, and on the soil
chemical properties.
MATERIALS AND METHODS
Experimental design
A field study was conducted in summer 1991 and 1992 on a Cecil
sandy clay loam in Griffin, Georgia. Following a long fallow during which
grasses were the predominant vegetation, the soil was planted to potato for
one year, then wheat for 2 years prior to the experir:nent. In Summer 1990,
the wheat residues were removed, and soil was conventionally tilled to 30
cm soil depth before planting forage sorghum over the entire the area. This
was done to reduce spatial differences and to further depress soil nutrients
in order to increase the potential for observing treatment effects. After
harvest in early October 1990, the experiment was laid out as a split-plot
design in randomized complete blocks with 3 replicates.
Main-treatments,
which were immediately applied, consisted of conventional tillage (CT), no-
tillage bare (NTB), and no-tillage cover (NTC). Main treatments were re-

84
applied two weeks after the 1991 harvest for the 1992 experiment. Subplot
treatments, applied at planting, consisted of pure stands grain sorghum
[Sorghum bicolor (L.) Moench,cv. "Pioneer 8230"] fertilized (SF) and
unfertilized (S), peanut [Arachis hypogaea L., cV. "Southern Runner"] (G),
velvet bean [Stizolobium deeringianum Bort, vc. "Early Speckled Velvet
Bean"] (V), and mixed stands of sorghum/peanut (SG), and sorghum/velvet
bean (SV).
Grain sorghum and peanut were used 1) because of their high
importance as food and/or cash crops, and 2) because they are often
intercropped in tropical Africa. Velvet bean was used because of its
potential for fixing nitrogen and for proDucing heavy biomass for soil
improvement. This crop was once popular in Georgia for use as green
manure (USDA, 1957; Scott, 1946), but its use declined with decreased
cost of inorganic fertilizers.
Return to the use of velvet bean for soil
improvement can foster agricultural sustainability.
f\\JPK fertilizer (90 kg N,
45 kg P 0
and 67 kg KzO per hectare) was hand broadcasted in SF
Z
5
treatment about 20 days after emergence. Crops in mixtures were planted
in alternate double rows. Each subplot consisted of 8 rows, 75 cm apart
and 12 m long. Plants were about 10 cm apart within row. Plant
populations for all crops averaged 200,000 and 100,000 plants per hectare
in pure and mixed stands, respectively. Weeds were controlled as needed
during growing season by hoeing and during winter period by application of
0.56 kg/ha paraquat (1,1' dimethyl-4,4'-bibyridiniumionl. Crops were
planted and harvested on June 1 and October 28 in 1991, and on June 15
and October 16 in 1992, respectively.
Also, reduced rainfall was observed
during the 1992 growing season (Figure 1, Chapter 3) indicating that the
crops were disadvantaged in 1992 compared to 1991.

85
Soil pH and nutrient analysis
Soil samples were taken each year at 0-7.5, 7.5-15, 15-30, and 30-
45 cm soil depths for pH and nutrient analysis at planting and harvest.
These samples were allowed to air dry for several days, ground to pass a 2
mm stainless steel screen, and hand mixed to ensure a representative
sample during analysis. Samples were kept in soil sample bags until
laboratory analysis for pH, N, P, K, Ca, and Mg. Soil water and buffer pH
were determined on a 1: 1 soil/liquid suspension. Soil total N was
determined by a micro-Kjeldahl method which included nitrate [salicylic acid-
sodium-thiosultate modification (Bremner and Mulvaney, 1982)]. Soil
samples were also extracted with 1 M KCI for the remaining nutrient
analysis.
Plant dry matter and yield.
Plant biomass and grain yield samples were harvested over 2
randomly located 1 m2 (velvet bean) or 1 m row (peanut and sorghum)
samples from inner-most rows.
Samples were dried at 90 0e for at least two
weeks then weighed.
Samples were then ground to pass 1mm screen and
analyzed for nutrients as described above for soil samples.
Nutrient uptake
was calculated by multiplying nutrient concentration by total dry matter.
Biomass, nutrient uptake and yield data were analyzed by year, date of
sampling (when needed), tillagelresidue management system, intercrop and
crop, by statistical analysis system (SAS Institute, Inc., 1985). Soil
chemical properties were analyzed by date of sampling, tillagelresidue

86
management practice, crop treatment and depth, also using the SAS
program.
RESULTS AND DISCUSSION
Plant biomass production.
Mean separation among intercrops is presented in Table 1 for each
tillage/residue management system for 1991 and 1992. In general, overall
biomass production was lower in 1992 than in 1991 (Table 1, Figure 1),
probably due to 1) unfavorable rainfall distribution, 2) late planting, 3)
reduced nutrient uptake, and 4) reduced soil nutrient content in 1992
compared to 1991. Overall final crop biomass prod uction was comparable
between CT and NTC in 1991, and between NTC and NTB in 1992. The
least biomass production was obtained from NTB in 1991, and in CT in
1992. Mean separation among crops was not affected by tillage/residue
management practices (Table 1), indicating that interaction between
intercropping and tillage/residue management was insignificant. Of the three
monocrops, the biomass production was the highest for velvet bean,
followed by sorghum and peanut (Table 1, Figure 1). Biomass production by
velvet bean was more rapid than that by sorghum or peanut all through the
season, with greater growth rate after about 60 days post emergence
(Figure 1), and resulted in early ground cover by the canopy. Velvet bean
residue dry weight averaged 11393 kg/ha and 9544 kg/ha in 1991 and
1992 respectively (Table 1). Such high biomass production by velvet bean

87
has been reported by previous workers who suggested the use of this crop
for improving soil fertility (Bowen et al., 1988; Malik et al., 1985; Burle et
al., 1992). The rapid spread of the velvet bean canopy suppressed weed
growth, also supporting its use for weed control (Baryeh, 1987). As a result
of intercropping effects, the overall biomass produced in the mixed stands
were intermediary between corresponding sole crops (Table 1), presenting
a n advantage over the less prod uctive intercrop component.
Intercropping tended to depress peanut biomass production compared
to peanut monoculture in both years (Figure 1; Table 1). Sorghum biomass
production remained unaffected by competition from peanut. In contrast,
intercropping favored velvet bean and depressed sorghum biomass
production in the sorghum/velvet bean mixture (Table 1). Overcompetition
of sorghum by velvet bean may be due to a greater water uptake by velvet
bean (Chapter 4).
Plant nutrient uptake
For the same reasons as for biomass production, overall plant nutrient
uptake was lower in 1992 than in 1991 in all tillage/residue management
systems (Tables 2 and 3, Figures 1 and 2). Figure 1 shows that N uptake
was particularly a function of the amount of biomass produced, indicating
that intercropping exerted little effect on crop nutrient concentration as
shown in Figure 2 for sorghum N content. In general, tillage did not
significantly affect nutrient uptake in 1991, because soil fertility was still
uniform for all plots. In 1992, nutrient accumulation in residues was
significantly greater in NTC than in CT and NTB except for P and Mg (Table

88
3).
In general, residue decomposition is enhanced in CT as compared to
NTC due to higher moisture content below the soil surface (Wilson and
Hargrove, 1986; Stott et al., 1986; Voroney et ai, 1989; Smith and
Sharp/ey, 1990). Reduced nutrient uptake in CT, may be attributable to 1)
reduced root growth, 2) reduced soil moisture content [Chapters 3 and 41,
and 3) rapid residue decomposition that may have resulted in greater
nutrient loss by leaching, immobilization or volatilization as reported Parker
(1986) for buried corn residues.
Reduced nutrient uptake in NTC may have
resulted also from slow residue decomposition due to water shortage on the
soil surface. Reduced uptake in KITS may have been compounded by
increased nutrient depletion (Figures 3, 4, and 5), as nutrient cycling was
reduced by residue removal.
Nutrient accumulation in crop residues was consistently higher in
velvet bean monocrop and/or in sorghum/velvet bean intercrop regardless of
the tillageiresidue management system in both years.
In 1991, the
unfertilized sorghum monocrop exhibited the lowest uptake of all nutrients
except potassium. The N uptake by monocropped sorghum was about 3 to
5 fold less than that of monocrop velvet bean for both CT and NTC in 1991
and for all tillage/residue management systems in 1992 (Table 3). In
general, intercropping improved overall residue nutrient content compared to
monocrop sorghum (Table 3). This observation is particularly important with
regard to nutrient recovery by the subsequent crops and to the long-term
soil nutrient status. Cereal residues often have a larger C:N ratio than
legumes and decompose more slowly with the risk of a net N immobilization
and reduced N recovery by the subsequent crops. In contrast, N recovery
from legume residue often is high because of more rapid decomposition and

89
larger amount of N release comparec to cereals (Frcnkenberger and
Abdelmagid, 1985; Douglas et al., 1980; Hargrove, 1986; Hargrove et aI.,
1990). Cereal residue decompositio~ is slow and often results in a net
immobilization, reducing plant N uptake. The rate of decomposition and the
amount of N recovered from cereal residue however, can be enhanced by
improving the initial soil inorganic N content (Smith and Douglas, 1968). In
cereal/legume mixtures therefore, rapid mineralization of legume residues can
provide sufficient inorganic N in favor of cereal residue mineralization, if an
adequate cereal/legume ratio is used.
In any case, resulting mixed residue
from intercropping may decompose at an intermediate rate, reducing
excessive losses and supplying plants with nutrients at a more optimal rate
than monocrop residues. Overall, residue return to the soil from legume-
based mixtures can have a long-term buffering effect on cereal nitrogen
uptake, contributing to agricultural s .Jstainability.
Grain or seed yield
In crop production, the ultimate aim of all cultural practices is to
optimize seed yield. Absolute grain or seed yield was lower in 1992 than in
1991 (Table 4). Reasons for this reduced yield may be the same discussed
earlier for reduced biomass production or nutrient uptake. Late planting,
resulted in late maturation and reduced velvet bean pod filling due to early
frost that occurred in late September.
In general, in 1991, yield was higher
in CT than in NTC and NTB certainly because of greater nutrient uptake. In
1992, increased water shortage provided yield advantage to NTC except for
I
velvet bean monocrop.
I
I
I

90
Absolute yield of sorghum was not significcntly affected by
competition from peanut except in NTB in 1991 and CT in 1992. In
contrast, although peanut pod yield was not affected by intercropping in
NTC and NTB in 1991, it was significantly depressed in all tillage/residue
management systems in 1992.
Peanut yield depression by companion
cereals has been extensively reported (Koli, 1975; IRAT, 1978; Reddy et al.,
1988; Ikeorgu and Odurukwe, 1989).
In general, shading effect and more
aggressive root competition from cereal companion crops often are cited as
reasons for intercropped peanut yield reduction (IRAT, 1978; Reddy et al.,
1988; Stirling et al., 1990). In this Erxperiment, short stature sorghum
variety was used and intercropping was done in alternate double rows to
minimize shading effect .. In addition, no major disease or insect infestation
was observed during the two years that could have differential impact on
crop treatments. Therefore, intercropped peanut yield depression may have
resulted essentially from competition from sorghum for below ground
resources.
As for the biomass production, intercropping favored velvet bean yield
production and tended to depress sorghum yield ,"vhen the two crops were
mixed.
Velvet bean is a viney crop that grows fast and produces heavy
biomass as shown in Table 1 and Figure 1.
Although velvet bean root
density may be lower (Chapter 3), its rate of wate r and nutrient uptake may
be higher than that of sorghum, providing it with a superior competitiveness
over sorghum. Velvet bean vines were cut when needed to keep them from
climbing the sorghum stems.
Shading from either intercrop was limited due
to 1) the height of velvet bean canopy, 2) the short stature of the sorghum
variety used, and 3) the binary planting strategy cdopted.
As with peanut,

91
only competition for below ground resources may have influenced intercrop
yield performance. Reduced yield of monocropped as compared to
intercropped velvet bean may have resulted from increase intra-crop
competition.
The dense canopy in velvet bean monoculture also may have
reduced air renewal, promoting air humidity and diseases which can
adversely affect flower and pod setting,
Relative yield of intercrops, e.g, actual yield calculated in relation to
the percentage of land area allocated to the crop in the mixture. was always
lower than the yield in pure stand because individual companion crop plant
population wasilalf the plant population in the monoculture.
The values of
efficiency of yield production (EYP) presented in Table 4 provide a fair
comparison between intercrop relative yields and their yield in monoculture.
Except for intercropped sorghum in 1991 and intercropped peanut in 1992,
EYP's approximated or were greater than 0.5 in all main plots, indicating
that intercropping favored yield production of component intercrops. The
sums of EYP's of associated crops represents the land equivalent ratios
(LER) and were greater or close to unity (Table 5), evidencing an overall yield
advantage of intercropping as reported by several previous workers (Fisher,
1977; Nyambo et ai., 1980; Ikeorgu and Odurukwe, 1989).
Effect of intercropping and tillage/residue management practices on soil
nutrient content.
I
l
In general, soil nutrient content was uniform across the experimental plots at
the beginning of the experiment in 1991 and decreased with soil depth
I
except for magnesium (Tables 6,7, and 8). Soil water pH was about 5.7-
I
I
I

92
6.2 and varied little vertically in the soil profile, indicating that lime/or
fertilizers may have been applied in previous years.
After two years of
treatment application, all soil nutrient content decreased to more than half
their initial levels (Tables 6, 7, and 8).
A significant loss of N, K from the
top 7.5 cm soil depth was observed in CT and NTB, compared to NTC
(Table 8). Reasons for this drastic decrease may include 1) plant uptake, 2)
slow nutrient turn over, 3) nutrient exportation with harvested grain, and 4)
various other sources of losses such as leaching, drainage with runoff water
and erosion. In general, NTC tended to exhibit higher Ca and Mg content
than CT and NTB (Tables 7 and 8). These differential effect of
tillage/residue management practices on soil nutrient content explains the
changes in soil pH levels as shown in Tables 7 and 8).
As a result of higher
nutrient and probably organic matter content, NTC soil exhibited a
significantly higher pH than NTB and CT soils at the end of the experiment.
However, the status of soil pH and nutrient content observed at the last
harvest may be a punctual result from plant uptake during the growing
season. Residue return to the soil in CT and NTC resulted in cyclic
replenishment of soil nutrients as shown in Figures 3 and 5 for Nand K.
Soil pH also followed the same trend.
Crop residue removal from NTB
reduced nutrient cycling, resulting in a continual decrease of soil nutrient
content.
Crop treatments exhibited little differences with regards to soil
nutrient content (Tables 9, 10 and 11, Figures 3, 4, and 5) due to the short
experimental period. Additional nutrient release from the 1992 residues in
CT and NTC would probably improve soil nutrient, especially N content in
the legume soils, compared to NTB.
Although the effect of velvet bean on

93
soil properties was not clearly demonstrated during this experiment, the high
biomass production and high N return to the soil by velvet bean, combine
with its good soil coverage to make it a crop of choice for soil and water
conservation. Velvet bean appeared to provide better soil N advantage than
peanut.
CONCLUSION
In general, plant biomass production, nutrient uptake and grain yield
drastically decreased in the second year of the experiment as a result of
unfavorable rainfall distribution, late planting and reduced soil nutrient
content.
On the average, CT favored plant biomass production, nutrient
uptake and yield in 1991 where rainfall distribution was satisfactory.
NTC
was advantageous under the drier conditions in 1992. Although NTB
differed little from NTC, soil nutrient content and pH in NTB suggested that
residue removal may lead to a long-term soil infertility.
Velvet bean biomass
production and nitrogen yield were interestingly high, encouraging the use of
this crop for improving soil properties. In general, intercropping improved
the residue quality and provided an overall yield advantage over
monocultures.
Interactions between intercropping and tillage/residue
management systems were generally significant and complex.

Table 'i.
Effect of tillage and residue management on the amount of crop residue incorporated (CT). removed
(NTB). or left on soil surface INTCI after harvest for 1991 and 1992.
Crop
Treatment
~
NTC
NTB
Mean'
1991
SF
8747
b
8862
c
8569
b
8693
c
S
8543
b
9015
c
8626
b
8728
c
SG
7339
c
7259
d
7664
c
7421
d
G
6058
d
7130
d
6058
d
6415
e
SV
11622
a
10527
b
9059
b
10403
b
V
12020
a
11443
a
10717
a
11393
a
S
8543
a
9015
a
8626
ab
8728
a
S/SG
8536
a
8351
ab
9575
a
8821
a
S/SV
9138
a.
8193
b
7165
b
8165··b
G
6058
a
7130
a
6058
a
6417
a
G/SG
6142
a
6168
b
5752
a
6021
b
V
12020
b
11443
b
10717
a
11393
b
V/SV
14106
a
12860
a
10953
a
12640
a
Average
9055
a
9040
a
8449
b
8832
1992
SF
8617
b
8071
b
6890
b
7859
b
S
599
d
5752
c
7021
b
6194
c
SG
3970
e
5402
c
4484
c
4619
d
G
3565
e
4702
c
4702
c
3988
d
SV
6399
c
8710
ab
7934
ab
7681
b
V
9550
a
9700
a
9383
a
9544
a
S
5599
a
7371
a
7021
a
6664
a
S/SG
5030
ab
7043
a
6212
b
6095
ab
S/SV
4681
b
5752
b
6802
ab
5745
b
G
3565
a
4702
a
3696
a
3988
a
G/SG
2909
b
3762
b
2756
a
3142
b
V
9550
a
9700
a
9393
a
9544
a
V/SV
8117
b
10050
a
9067
a
9078
a
Average
6283
b
7056
a
6736
ab
6636
- Means of same set within column with same lerter are not significantly different (a = 0.05) .
• Means for SG and SV represent averages of combined component inter crop biomass .
•• Means for specified component intercrop in indicated mixture IS/SG = sorghum/groundnut mixture).

Table 2. Crop residue nutrient content at harvest (kg/ha) average cover crop treatments.
CT
NTC
NTB
Averaqe
Nutrients
~
1992
1991
1992
11991
1992
1991
1992
N
138.4
ala)
99,6
u(b)
, 37,7
ala)
120,3
ala)
123,9
bra)
106,5
b(a)
133,3
(a)
108,8
Ib)
P
12,2
11(/1)
8,2
11(11)
12,5
11(11)
9,6
u(Il)
10.9
11(/1)
9,9
/l(1I1
'1.9
(/I)
9 ,,"",
(Ill
K
178,6
ala)
86,1
bib!
165.7
b(a)
1051
a(b!
152.7
cIa)
83.4
bIb)
165,7
(a)
91.6
(Il)
Ca
73.8
ala)
49,7
blbl
67.2
bra)
589
ala)
61.4
c(al
49.3
bIb}
67.5
(a)
52,6
(a)
Mg
28,0
ala)
16.7
a(b)
26.0
ab(a)
19,5
a(bl
23.3
b(a)
18.4
ala)
25.8
(a)
18,2
lu!
Means within row for same year with same letter Wltt10ut parentheses are not significantly different,
Letters in parentheses represent year separation.

Table 3.
Effect of tillage and intercropping on crop residue nutrient content at harvest (kg/hal.
Crop
N
p
K
Ca
Mq
Treatment
CT
NTC
NTB
CT
NTC
NTB
CT
NTC
NTB
CT
NTC
NTB
CT
NTC
NTB
1991
SF
69
c
58
rl
112
A
9
a
9
a
9
b 203
a
206
a
205
a
31
d
32
d
30
c
25 a
24
iJ
20
c
s
47
c
50
d
77
a
9
a
9
a
9
b 207
a
187
ab 191
ab
30
d
29
d
30
c
23 a
24
a
22
be
I
SG
1 1 1
bc
108
c
9 1
0
11
a
13
a
10
"b167
ob
139
b
135
ab
54
cd
55
c
49
c
27 a
29
H
27
"
G
156
b
190
b
110
ft
9
tI
11
a
10
"b 1 14
c
138
b
1 1 7
b
73
bc
7 5
bc
74
b
30 tI
31
"
3 3 "
SV
'72
b
164
b
118
a
15
a
11
a
13
ab208
a
181
ab 150
ab
97
b
79
b
72
b
34 a
25
it
19
c
IJ
270
a
260
a
132
a
18
a
17
a
16
a
155
be
154
ab 139
ab156
a
132
a
109
a
125 a
23
a
20
c
1992
SF
106
b
90
bc
72
b
14
a
l O a
9
a
108
a
133
a
98
a
148
a
51
bc
97
a
28 tI
28
a
18
it
s
56
c
46
c
66
b
8
b
9
fl
16
a
60
b
90
a
107
a
88
c
20
c
107
a
16 b
17
a
23
it
SG
61
c
82
be
67
b
6
bc
7
a
7
;)
45
b
75
a
66
a
63
de
34
c
66
a
13 b
13
H
16
iJ
G
90
b
119
bc
99
b
4
c
6
a
5
a
34
b
75
a
58
a
50
e
45
bc
58
a
18 b
18
a
19
iJ
sv
107
b
158
ab140
b
8
b
12
a
11
a
50
b
137
a
88
a
83
cd
78
b
88
a
14 b
21
a
18
a
v
209
a
226
a
221
a
12
tI
13
a
13
a
33
b
119
a
98
a
112
b
131
a
93
a
17 b
18
a
18
a
Means with columns with same letter are not significantly different (0
0.051.

Table 5. Effect of tillage and residue management on land equivlent ratios (LER) with regard to seed yield of intercrops.
CT
HTC
HTB
OVerall
Intcrcropping
--.!2'Z.L
_. 1992
--.!2'Z.L
1992
~
1992
1991
1992
SG
1.2
1.1
1.1
1.1
1.0
0.8
1.1
SV
1.2
1.2
1.2
1.8
1.2
1.5
1.2
1.5
LER = Ma/Sa + Mb/Sb = La + Lb
~here Ma and Mb = Relative yield of crop A and B in mixture respectively.
Sa and Sb = Yield of crop A and 8 in monoculture respectively.
La and Lb = Efficiency of yield production (EYP) presented in Table 4 for intercrops A and B respectively.

TabLe 6. SoiL profiLe nutrient status in 1990 and 1992 average over tiLLage and crop treatments.
Depth
pH
H,O
pH lleOH
N
P
K
Ca
Mg
7/25/90
0.75
5.88b
7.66a
0.11 a
15.6a
137.2a
619.2b
79.7a
7.5-15
5.86b
7.65ab
0.09ab
13.6a
96.3b
683.6a
86.8a
15·30
6.12a
7.64ab
0.08b
6.3b
I
54.4c
525. le
95.6a
30-45
5.99ab
7.62b
0.05e
2. le
36.6d
360.4d
85.5a
11/17/92
0.75
5.81b
7.71a
0.07a
8.3a
52
a
369.5b
39.3b
7.5-15
5.99a
7.70ab
0.06b
7
a
34.4b
417.8a
40.1b
15-30
6.05a
7.68b
0.04c
2.3b
32.1 b
338.2c
41.4b
30-45
5.85b
7.64c
0.03d
0.7b
27.3c
280.9d
49.3a
Means within columns with same letter are not significantly different (a = 0.05).

Table 7. Effect of tillage and residue management on soil nutrient content (X).
Average over crop treatments and depths.
Tillage
pi!
H,O
Buffer pi!
N
P
I(
Ca
Mg
...-_._---
7/25/90
CT
5.95ab
7.6a
O.OB~
B.7ab
BOa
532a
79a
NTC
6.05~
7.6a
O.OBa
B.2b
i
Bla
563a
lO1a
NTB
5.B9b
7.6a
O.OBa
11.1 a
8la
545a
80a
1'/17/92
CT
5.85b
7.67b
0.05a
4.5ab
39a
343a
41b
NTC
6.07a
7.71a
O.05a
3.Bb
39a
363a
46a
NTB
5.B6b
7.6Bb
0.04b
5.4a
31b
356a
41b
Means within columns with same letter are not significantly different (a = 0.05).

Table 8.
Effect of tillage and crop residue management system on soil profile nutrient content (ppn).
Average over crop treatments.
pH
0-7.5 cm
7.5 - 15 cm
15.3 cm
30 - 45 cm
Nutrients
CT
NTC
NTH
CT
NTC
NTH
CT
NTC
NTH
CT
NTC
NTB
7125/90
pH Hp
5.84a
5.81JiJ
5.900
5.920
5.98a
5.70a
6.09a
6.17a
6.09a
5.96b
6.17a
5.85b
Buff rH
7. (')0
7.Mo
7.660
7.('5"
7.66£1
7.Mo
7.69..
7.{,50
7.630
7.610
7.61n
7.62(\\
N
0.06b
0.07b
0.12a
0.12a
0.0ge
O. lOb
0.09a
0.08ab
0.07b
0.05a
0.05a
0.048
p
15
a
14
a
18
a
13
a
12
a
16
a
50
a
5.76a
7.86a
1.95a
1.81a
2.63a
K
133
a
135
a
144
a
98
a
99
a
92
a
50 I a
59
a
53
a
41
a
33
a
36
a
Ca
596
a
630
a
630
a
693
a
682
a
677
a
485
b
529
ab
559
a
353
ab
383
a
345
a
Mg
75
a
83
a
80
a
85
a
90
a
85
a
70
a
140
a
76
a
86
ab
91
a
80
b
11/17/92
pH H,O
5.87a
5.85ab
5.73b
5.89b
6.08a
6.01ab
5.91 b
6.24a
5.99b
5.74b
6.1 a
5.73b
Buff pH
7.66c
7.75a
7.71b
7.70a
7.71a
7.71a
7.69 a
7.67a
7.67a
7.65a
7.64a
7.65a
N
0.06b
0.090
0.07b
0.06 ..
0.060
0.06a
0.05 a
0.04b
0.04b
0.03"
0.03a
0.03a
p
7.8 a
7.5 a
9.6 a
6.2 ab
5.9 b
9.02a
3.16 a
1.34b
2.29ab
O.77a
0.60a
0.60a
K
47
b
60
a
49
b
41
a
36
b
25
c
39
a
33
a
25
a
29
a
28
a
24
a
Ca
362
a
372
a
374
a
399
a
422
a
433
a
345
a
339
a
331
a
269
b
319
a
285
b
Mg
36
a
44
a
38
a
41
a
40
a
39
a
41
a
44
a
39
a
46
a
55
a
47
ab
Means within columns with same letter are not significantly different (a = 0.05).

Table 9.
Effect of intercropping on soil nutrient content (ppm).
Average over ti llage/residue management systems.
Crop
Treatment
pH
H O
Buff pH
N
P
I::
ca
Mg
2
7/25/90
SF
6.0 ab
7.64a
0.083
8.43a
83a
553a
83a
S
5.93ab
7.65a
0.08a
11. 95a
76a
539a
80a
SG
5.83b
7.64a
0.08<1
5.40a
79a
524a
83a
G
5.953b
7.63a
0.070
8.70<1
82a
535a
81a
SV
5.43<1b
! .650
0.090
9.18a
83a
5528
80a
V
6.11a
7.648
0.08a
9.72a
I
83a
579a
113a
11/17/92
SF
5.89bc
7.70a
0.05a
5.9Ba
38a
348ab
37b
S
6.01ab
7.71a
0.05a
4.88ab
34bc
358ab
45a
SG
6.03a
7.68ab
0.05a
4.26ab
32c
373a
45a
G
5.79c
7.68ab
0.05a
4.35ab
39a
338b
41ab
SV
5.89bc
7.66b
0.05a
3.27b
38ab
347ab
44a
V
5.95ab
7.68ab
0.05a
4.67ab
38a
360ab
44a
Means within columns with same letter are not significantly different (a = 0.05).

Table 10.
Effect of intercropping on soil nutrient content (PPm). averaged over depths and tillage/residue management systems.
pH
0-7.5 cm
7.5-15 cm
Hutr;rnl!l
Sf
S
Sli
G
SV
V
Sf
S
SG
G
SV
V
7/25/90
pH H)O
5.93 a
5.83 ab
5.87 ab
5.87 ab
5.75 b
5.99 a
5.97 a
5.93 a
5.33 a
5.96 a
5.86 a
6.12 a
Ruff rH
7.f>f> fl
7.b7 n
7.b7 n
7.M fl
7.b5 fl
7.M ,1
7.b7 n
7.M n
7.62 fl
7.f>4 fl
7. f,5 h
7 . t)~J I1
N
O.OC; Q
0.06 a
0.10 a
0.08 a
0.10 n
0.10 Q
0.11 8
0.10 a
0.11 a
0.106a
0.113a
0.101 fl
P
14.33 a
18.03 a
15.46 a
13.95 a
15.02 a
15.79 a
12.47 a
17.68 a
11.98 a
12.64 a
12.33 a
14.24 a
K
139.65 a
112.28 a
148.49 a
133.93 ab
146.17 a
144.17 a
102.26 a
89.48 a
97.79 a
97.50 a
99.31 a
91.04 a
Ca
641.41 a
590.27 ab
627.63 ab
571.49 b
636.08 ab
647.48 a
706.55 ab
652.56 b
654.87 ab
667.22 ab
676.63 ab 240.44 a
Mg
84.76 a
75.39 a
82.09 a
75.44 a
78.'i9 a
81.47 a
88.33 a
80.48 a
87.33 a
86.91 a
84.67 a
92 .82 a
I
11117/92
pH Hp
5.6
c
5.9
ab
5.98 a
5.8
ab
5.77 bc
5.84 ab
6.0
ab
6.07 ab
6.13 a
5.84
b
5.92 ab
6.0
ab
Buff pH
7.72 a
7.73 a
7.72 a
7.70 a
7.70 a
7.70 a
7.72 a
7.70 a
7.72 a
7.69
a
7.68 a
7.73 a
N
0.07 ab
0.06 b
0.06 ab
0.07 ab
0.07 a
0.07 a
0.06 ab
0.05 b
0.06 ab
0.068
0.06 a
0.06 ab
p
12.99 a
8.74 ab
7.16 b
7.54 b
5.52 b
7.91 b
7.5
a
8.08 a
6.79 ab
6.77
a
5.16 a
7.95 a
K
48.31 bc
46.29 c
46.28 c
54.87 b
51.55 bc
64 .68 a
36.19 ab
33.52 ab
31.76 ab
38.43
a
35.81 ab
30.62 b
Ca
338.96 b
401.29 ab
393.27 a
358.92 ab
352.22 ab
372.32 ab
417.56 a
423.94 a
436.33 a
399.86
a
395.49 a
433.62 a
Mg
29.07 b
43.01 a
43.97 a
41.01 a
38.48 ab
40.00
36.33 a
42.06 a
42.32 a
37.41
a
38.58 a
44.11 a
Means within columns with same letter are not significantly different Ca = 0.05).

Table 11.
Effect of intercropping and tillage/residue management practices on soil pH and nutrient content (kg/ha).
Average over depths.
Crop
pHw...
N
p
K
Ca
"g
Treat-
_
ment
CT
NTC
NTB
CT
NTC
NTB
CT
NTC
NTB
CT
NTC
NTB
CT
NTC
NTB
CT
NTC
NTB
1991
SF
5.99a
6.1b
5.9ab
0.09a
0.07a
O.OBa
10.Ba
7.6a
7.3b
100a
32d
77be
587a
567a
517bc
79.7a
92.6a
79.2ab
S
5.83a
5.95c
6.00a
0.08a
0.08a
0.09a
8.00
8.0a
8.8a
66c
29d
70e
473b
550a
608a
74.3a
85.5a
80.3ab
SG
5.97a
6.13ab
5.39b
0.09a
0.08i1
0.08a
8.2a
8.9a
8.1b
89ab
79ab
90ab
530ab
556a
486c
85.2a
87. 2a
78.1 ab
G
5.82a
5.95c
6.14a
0.07a
0.09a
0.07a
7.4a
8.0a
10.6b
81abc
86ab
79bc
473ab
536a
595ab
74. 7a
80.90
87.Ba
sv
6.02/1
5.115c
5 .91. fib 0.090
0.090
0.08/1
9.10
9. Sa
1I.9b
70be
78A
75he
586A
56711
513c
78.Bil
86.511
71.. 1b
I
v
6.09a
6.28a
5.94ab 0.07a
0.08a
0.08a
8.7a
7.4a
13. lab
73b
78b
97a
573a
604a
561abc
82.4a
73.7a
83.3ab
1992
SF
5.87a
6.05b
5.77a 0.05a
0.05a
0.15a
7.4a
5.0a
5.5ab
51a
38be
25b
357a
368ab 316b
36.9b
43.0bc
31.2e
s
6.00a
6.32a
5.92a 0.05a
0.05a
0.04b
3.1b
3.3b
8.2a
36c
37bc
28b
373a
401a
366ab
44.5a
48.3ab
41.2ab
SG
5.94a
6.11b
5.84a
0.05a
0.05a
0.05ab 4.4ab
3.2b
5.1ab
35c
33c
29b
347b
361ab 344ab
44.5a
50.3a
40.3b
G
5.67b
5.82c
5.89a 0.05a
0.05a
0.05ab
4.4b
4.3ab
4.4ab
37bc
42ab
37a
340ab
327b
348ab
41. 3ab 40. 8c
40.3ab
sv
5.82a
5.99b
5.86a 0.05a
0.06a
0.05ab
2.8b
4.2ab
2.8b
35c
35bc
28b
308b
362ab 369ab
40. 8c
45. 6abc 43. 8ab
v
5.82a
6.12b
5.92a 0.05a
0.05a
0.05ab
4.7ab
3.1b
6.2ab
41b
50a
37a
332ab
359ab 391 a
38.3ab 47.2abc 47.8a
Meo~s with columns with same letter are not significantly different Ca = 0.01).

Biomass
«112,000-
VIS'!,'
1992
L:
........
1991
0>
"
"
6
.S
.....
8,000
ID
,/··········1·
"
....
G_.:
,
.. '
,.'
~.. -'
1i1
E
';'~"
-:::"-:::'G/SG
I
~ 4,000-
~..~ ..~..
-'
'
"'0
::::.::::...
--
--
_"-"-"-"-
0..
e
0 1 e~!
!
!
I
20
40
60
80
100
120
140
o
20
40
60
80
100
120
140
N uptake
300
cu
.c
........
(J)
,
1
,
~
.....,.
200
ID
~
I
- . -.
,
eu
,
,
-Q. 100
:::J
-.,- ...,J .;c::'~ -
- - - -
J,.' .....:.-_._ .. - .. - --1
.. -
Z
;9::-"-
.. - .. -
.
40
60
80
100
120
140 20
40
60
80
100
120
140
Days after planting
Figure 1: Effect of intercropping on plant biomass production and N uptake.
Error bars indicate LSD(O.05).

Nitrogen concetration
5
1991
1992
4
~c 3
.Q
~
C
Q)
2
u
C
0
U
Z
~o
40
60
80
100
120
140
20
40
60
80
100
120
140
N uptake
, . . . . - - - - - - - - - - - - - - - - - . ,
•
i
120
1992
1991
(ij
E
01
..>::
-;
80
..>::
III
l i
.------
::J
Z
40
I ~
S/~~
S!~V I
40
60
80
100
120
140
20
40
60
80
100
120
140
Days after planting
Figure 2: Effect of intercropping on sorghum N concentration and uptake
Error bars indicate LSD(O.05).

6 . 4 . - - - - - - - - - - - - - - - - - - - - - - ,
6.2
CT
Planting 2
Harvest 1
arvest 2
6
5.8
S
G
V
SG
SV
5.6
6.4 . - - - - - - - - - - - - - - - - - - - - - - - ,
NTB
I
6.2
a.
T
.
~
-
-
.
2 6
--
-
//~ ~..~.:~ .
~
~
- -
I
/
.;;;...---
""? -:...
I ·:~~:·:_·~·-·.;·~ .. · .... ·I .... ··/ ..:;.;.:
.
\\'~.:-
~
._......,
.""'"
,
"
'05.8
..... .....
._-~.....:..-.~
'. .
..........
i /
\\
Cl)
.....
I
'L
5.6
6.4 . - - - - - - - - - - - - - - - - - - - - - - - ,
NTC
6.2
..,-J//1~;;~:=:>\\
6
. '
, .
--
t
~. _...:.:.,' .:.:..... y// , . .
'\\1
, ... "
,
~
.
,: "
~
5.8
r---
I / "
-
I"
_.._~.:...~.......,..._..__/. ",
5.6
......... i,'
.....
o
5
10
15
20
25
30
35
Time (months) from start of experiment
Figure 6: Effect of intercropping and tillage/residue
management on soil water pH in the top 7.5 cm soil depth.
Error bars indicate LSD(O.05).

140
Planting 1
eT
120
100
80
60
40
20 '--------'-------'------'-------'-------'-----'---'
-Ea.. 140
a..
NTB
-~ 120
Q)
.0
100
(ij
Q)
0)
80
c
(ij
.c
60
u
x
Q)
S
G
V
SG
SV
40
' -
0
I
Cl)
20
140
120
100
80 -
60
40
200
5
10
15
20
25
30
35
Time (months) from start of experiment
Figure 5: Effect of intercropping and tillage/residue management
l
on soil extractable K level in the top 7.5 cm soil depth.
Error bars indicate LSD(O.05).
r
l
I,
I:

20
Planting 1
eT
T.
16
k'·
,~,.
I..
~:.:.;.-.... Harvest 1
Planting 2
12
----
8
~~~::~~~~~-~~~~J:::~J HaNes"
- - .. -
I
- . .
..-..-.._..__.._..-
- 4
E
&20
-a..
NTB
ID16
..Q
ro
8>12
c
ro
.c
0
8
x
ID
'0 4
en
20
NTC
T~.,
.
16
.~'..::..'~- - -} ,,'
" ,
.....
"', ',-,
'.
...
,
'T
. . .
".
12
..', ,-. , "'.j.
'<~ '--- ..,,<:: - :- f- .
'-0
8
G V
s
~SG §YJ"'~:~~--
4
o
5
10
15
20
25
30
35
Time (months) from start of experiment
Figure 4: Effect of intercropping and tillage/residue management
on soil extractable P level in the top 7.5 cm soil depth.
Error bars represent LSD(O.05).

1 4 . . - - - - - - - - - - - - - - - - - - - - - ,
CT
12
Planting 2
..:/.-.-.~.&:rI.~ ..=_:. "',
10
T-----------'\\:.
Planting 1
.,/'"
8
6
~ Harvest1 /:'" ,
'~~;:.
,6'
"""_
.~.~..=..=..:;~.::..;;::::~F
' \\ Harvest 2
4L.-----'------'------....L---J......------'-------'-----"----'
1 4 . - - - - - - - - - - - - - - - - - - - - - ,
-~12
···1
G
+-'
s
y
.,
~~ f}Y I
a310
~"
+-'
."'.
...........
c
NTB
~'"
-I
......~~..
-I
8 8
·........;:····1· .. ·
.......~_. ~"':~' '"' -1- -. ~ ~ ~
z
-~,
-~
........... _-
CO 6
+-'
.9 4 L--_---'-_ _......L-_ _""'----_ _~___..L_ ____'__ _--'-----'
.-
c 7 5 1 4 . - - - - - - - - - - - - - - - - - - - - - ,
12
NTC
10
8
6
40
5
10
15
20
25
30
35
Time (months) from start of experiment
Figure 3: Effect of intercropping and tillage/residue management
on soil total N level in the top 7.5 cm soil depth.
Error bars indicate LSD(O.05).

111
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112
Frankenberger, Jr., W.T., and H.M. Abdelmagid.
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113
grain protein content of 'Clarck' barley (Hordeum disticum L.)
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115
Trenbath, B.R.
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Am. J. 50:1251-1254.

CHAPTER 6
CONCLUSIONS
Grain sorghum [Sorghum bicolor (L.) Moench,cv. "Pioneer 8230"] was
intercropped with peanot [Arachis hypogaea L., cv. "Southern Runner"tor
velvet bean [Stizolobium deeringianum Bort, vc. "Early Speckled Velvet
Bean"] under conventional tillage (CT), no-tillage with residue cover (NTC) or
no-tillage bare (NTB) in 1991 and 1992 to examine the effect of
intercropping and tillage/residue management practices on plant root growth,
biomass and yield production, soil water content and soil chemical
properties.
Results from this study further confirmed the effect of tillage/residue
management on crop root growth. Root length density (RLD) and root dry
weight (ROW) were higher in NTC and NTB than in CT, and this was largely
attributed to higher soil moisture content. All crop treatments produced
significantly more roots in the top 10 cm depth than deeper. In the CT,
however, a greater proportion of the total root population was observed in
the 20-30 cm soil depth as compared to the NTC and NTB. Sorghum
produced more roots followed by velvet bean and peanut. lntercropping
resulted in intermediary root proliferation between component sole crops,
116

11 7
and tended to favore sorghum over the legumes. Root growth was greater
in 1992 than in 1991, despite the reduced rainfall in 1992, and this was
attributed to possible stimulative effect of the water shortage and changes
in soil fertility over time. The ratio of the ROW to the RLO suggested that
finer roots were produced in 1992 compared to 1991.
The measurement of soil water content by time domain reflectrometry
clearly confirmed the moisture disadvantage of conventional tillage over no-
tillage systems.
Crop residue removal from no-tillage plots resulted in
insignificantly less soil water content than otherwise. These differences
corroborate the water infiltration measurements.
Reduced soil"watereontent
in mixtures suggested a greater soil exploration and a more thorough water
use by intercrops when compared to sorghum monocrop. Increased
competition for water between sorghum and either legume in the mixtures
appeared to occur at 45-60 cm soil depth.
In general, plant biomass production, nutrient uptake and grain yield
drastically decreased in the second year of the experiment as a result of
unfavorable rainfall distribution, late planting and reduced soil nutrient
content. On the average, CT favored plant biomass production, nutrient
uptake and yield in 1991 where rainfall distribution was satisfactory. NTC
I
was advantageous under the drier conditions during the 1992 growing
~
season. Although NTB differed little from NTC, soil nutrient content and pH
in NTB suggested that residue removal may lead to long-term soil infertility.
I
Velvet bean biomass production and nitrogen yield were interestingly high,
encouraging the use of this crop for improving soil properties. In general,
I
intercropping improved the residue quality and provided an overall yield
advantage over monocultures.
I
I
I
I

118
Despite the differences between years, most treatment comparisons
were unaffected. In general, interactions between intercropping and
tillage/residue management systems were significant and complex,
suggesting a careful selection of intercrops and soil management systems
for satisfactory crop production.