Soil moisture changes and maize productivity under alley cropping with Leucaena and Flemingia hedgerows at Chalimbana near Lusaka, Zambia

Forest Ecology and Management ELS EV I ER

Forest Ecologyand Management 64 ( 1994) 231-243

Soil moisture changes and maize productivity under alley cropping with Leucaena and Flemingia hedgerows at Chalimbana near Lusaka, Zambia P.W. C h i r w a *,=, P . K . N . N a i r b, C.S. K a m a r a c =SADC/ICRAFAgroforestryProject,Makoka AgriculturalResearchStation, P.O. Rex 134, Zomba, Malawi bDepartmentof Forestry. IFAS. Universityof Florida. Gainesville.FL 32611. USA =SADC/ICRAFAgroforestryProject, ChalimbanaAgriculturalResearchStation, P/Bag CH8, Lusaka. Zambia

Abstract Soil moisture changes and maize yield were studied in 2-year-old alleys afLeucaena leucacephala and Flemingia macrophylla at Chalimbana, Zambia. Field tensiometers were installed at 15, 30 and 45 cm depth, in fertilized and unfertilized alleys within the double hedgerows, and the first, second and third rows of maize, and were monitored throughout one maize growing season in 1989/1990. In general, maize growth (indicated by height and dry matter measured at roughly fortnightly interval) was higher (P<0.01) in fertilized alleys than in unfertilized alleys, and there were no differences between Leucaena and Flemingia alleys. In both fertilized and unfertilized alleys, the maize plants were 20% shorter (P< 0.01 ) in the first row (nearer the hedgerows) than in the second and third maize rows. Maize dry matter yield was 30% more (P< 0.01 ) in unfertilized Flemingia alleys than in corresponding Leucaena alleys. The grain yield was similar in the fertilized alleys of Leucaena and Flemtngia. However, in unfertilized alleys, the grain yield in Flemingia alleys was 50% more than that of the corresponding Leucaena alleys. The fertilized alleys produced twice as much grain as unfertilized alleys when hedgerow prunings were added to the plots. The prunings as a source of nutrient did not appear to have any noticeable effect on crop productivity. The soil moisture content under both Leucaena and Fiemingia hedgerows was higher than under the maize rows in the alleys throughout the growing season. The study shows that, under conditions of low fertility and no addition of fertilizers, Leucaena is twice as competitive, as Flemingia for soil resources, and reduces yield of alley-cropped maize from 2.2 t ha- ~to 0.7 t ha- ~. If, however, fertilizer is added, there are no short-term differences between the two hedgerow species. Key words:Soil moisture; Maize; Alleycropping;Leucaenaleucacephala;Flemingiamacrophylla

1. Introduction Attempts to replace traditional shifting cultivation with mechanized farming for the produc*Correspondingauthor.

tion o f seasonal crops have largely been unsuccessful in Africa for both technical and sociocultural reasons (Kang and Wilson 1987; Nalr, 1990). This has led to the recognition o f inherent advantages o f traditional land-use practices consisting o f trees and crops in interacting

0378-1127/94/$07.00 © 1994Elsevier ScienceB.V. All rights reserved SSDI0378-1127(93)06054-9

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combinations. Improvement of traditional land use systems scientifically is a significant aspect of agroforestry research. As part of such a major initiative, the International Council for Research in Agroforestry (ICRAF) has initiated a series of agroforestry experiments in different ~arts of southern Africa~ co, lnt~es in association with national research ~stitu:ions. Two s':ch experiments were established in Zambia: one is to screen the various multipurpose trees; the other is an alley cropping trial involving Leucaena leucocephala, Flemingia macrophylla and Sesbania sesban (J.A. Maghembe et ai., 1988, unpublished data). This paper reports the resuits of an investigation from the latter. Most of the studies on alley cropping in Africa have been done in the humid tropics where moisture is not limiting (Lal, 1974, 1989; Kang et al., 1981, 1985; Kang and Wilson, 1987; Yamoah et al., 1986). This study was done in Zam-

bia, where rainfall is erratic and, on average, there are only 3 months when rainfall is greater than evaporation (Kamara and Mateke, 1989). Thus, periodic drought and consequent crop failures are common in these conditions. If crops are mixed with trees as in alley cropping, there is likely to be competition for moisture with the alleycropped plants under such conditions (Ssekabembe, 1985). During a season with below average rainfall in a semiarid region of India, yields of sorghum, c,'~stor and cowpea grown in leucaena alleys have been reported to decrease because of competition for moisture between the leucaena hedges and the crop (Singh et al., 1989). The objective of this study, therefore, was to monitor soil moisture depletion pattern in leucaena and flemingia hedgerow alleys and assess the productivity of alley-cropped maize compared with sole.cropped maize.

N

MetroR ~

1 0 . 0 IV

..q

(Rt,R2, RS)

Ter~mlw - ~

(15,

~JO,45 can)

11.0m

Fig. I. Schematicdiagramof;he experimemalunit and locationoftensiometers.

P. W.. Chirwa / ForestEcologyand Management 64 (1994) 231-243 250 [

233

Leucaena fertilized

|

150~-

'°°t

---

I

-

I

!

20

I

40

!

!

60

160 Loucaena

unfertilized

120

40

i

i

20

!

40

I

i

e~

!

e0

Fig, 2. Heightof maizein Rows 1-3 and controlrow in fertilizedand unfertilized maizegrownbetweenleucaenahedgerows. 2, Materials and meChods Table 1 Urea and prunings from leucaena and flemingia applied to the alleys for the 1989/1990 season Species

Leucaena Flemingia

Fertilizer (kgha -t )

0 150 0 150

Pruning biomass applied (kg ha-t of dry matter) First pruning

Second pruning

Total

2788 1266 1609 2043

1379 1485 485 455

4167 2751 2094 2497

2. I. Study site

The study was conducted at Chalimbana Agricultural Station in Lusaka Province of Zambia, located 28029'56" east and 15°21'32" south. The area has a mean annual rainfall of 800--900 m m and a crop growing period of 150 days. The rainfall for the 1988/1989 cropping season was 1224 mm while that for the 1989/1990 cropping season, when this study was conducted, was 776 ram. The maximum, minimum and mean annual temperatures are 22.3, 9.4 and 19.7°C, re-

234

P. rE. Chirwa/ ForestEcologyand Management 64 (1994)231-243 250 Flomingia fodilizod

20( 15C 100

I

I

20

/

I

40

I

I

flO

150 Flemingia unfodilizod

100

I

4'o

t

~

8o

I

~o

Fig. 3. Heightof maizeRows1-3 and rowof the controlin fertilizedand unfertilizedmaizegrownbetweenflemingiahedgerows.

spectively. The soils belong to the Katange geological system and the predominant rock underlying the area is quartz muscovite schist of the Chuga formation which is interbedded with quartzite horizon (Yager et al., 1967). The surface soils are slightly acidic (pH 5.7) while subsoils are neutral to alkaline (Kamara and Mateke, 1989) and have been classified as plinthic lixisols (Food and Agriculture Organization) which is the same as fine loamy, mixed isohyperthermic plinthic kandiustalf under US Department of Agriculture classification.

2.2. Plots

The alley cropping trial was started in 1987 with the establishment of the hedgerows. These hedgerows consisted of two tree species: Leucaena leucocephala (Lam. de Wit, hereafter called leucaena in this paper) and Flemingia macrophylla (Blume ex Miq., flemingia). The hedgerows were first pruned and applied in the alleys in the 1988/1989 cropping season. Hybrid maize variety (Zea mays MM603) was planted in the alleys. The design w~s a factorial split plot

P. W.. Chirwa / Forest Ecology and Management 64 (1994) 231-243

235

200 ~

DAP

180

160

140 i:~'x

12o

I O0

i

80

GO

Fert.ll[z~d

Ual~r~lllzed F~rt~lllze,t

Leuoaena

Utder%lllz~d

Flen'Llngia

Fig. 4. Maize height 62 DAP in fertilized and unfertilized maize between leucaena and tlen~ingia alleys. Bar graphs in each alley with tile same letter are not statistically different at P=0.05.

with two hedgerow species and two fertilizer rates: no fertilizer and 150 kg urea h a - ' as the main plot and maize rows as the subplot. Each treatment unit consisted of two do~Yole hedgerows spaced at 50 cm between and within rows, six rows of maize between them and three maize rows on both sides of the hedgerows (Fig. 1 ). The hedgerows were in the second season of pruning when the present study was conducted. The first pruning for the season at 50 cm height of the hedgerows was done approximately 2 weeks before planting and the prunings were incorporated into the soil during harrowing. The maize was planted at within and between row spacings of 25 and 75 cm. The maize rows next to the hedgerows were located 62 cm from the bedgerow. The plots to receive fertilizer had basal application ofdiammonium phosphate at 200 kg h a - l and split applications of 150 kg urea h a - ' - halfat 14 days after planting (DAP) and the second half at 35 DAP. The second hedgerow prun-

ings were applied as mulch 35 DAP. The amount of prunings for the first, second application and the total applied are given in Table 1.

2. 3. Maize growth and yield Maize heights of ten randomly selected plants on each row were measured at 19, 45 and 62 DAP. Sampling for dry matter was done at 29, 45 and 95 DAP on the three outside maize rows to represent the first, second and third maize rows from the hedgerow (Fig. 1 ). Each maize row of 9.5 m long was harvested separately for all the treatments. The final maize grain yield was calculated using a cob:grain ratio of 0.85, and corrected to a standard 13% moisture content,

2.4. Soil moisture potential On each plot, tensiometers were installed to depths of 15, 30 and 45 cm within each of the

236

P. W. Chirwa / Forest Ecology and Management 64 (1994) 231-243

250 Loucaona fertilized 20O 150;

50 020'

~'P~

i

i

40

i

60

i

i

80

i

100

t20 Loucaona unfmtlllzod

100 eo

} 8o

.,e..Rizw1 .e.. I~tta

/

,o 20

020

~ -

t

t

40

!

60

i

6'0

100

Fig. 5. Dry matter productionin maize Rows 1-3 and the middle maize row of the control plot in fertilizedand unfertilized maizegrownbetweenleucaenahedgerows. double hedgerows, in the first, second and third maize rows from the hedgerow (Fig. 1 ). Soil moisture potential was measured using a pressure transducer (Marthaler et al., 1983). The reading on the pressure transducer (RT) was the sum of the suction of the water column (LOH) in the tensiometer and pressure head (h). The relationship can be presented as: h = L O H - RT Measurements were made daily after every ma-

jor rain for 4-5 days and less frequently thereafter.

2.5. Data analysis The analyses of variance for a split plot design was done for maize height, dry matter and grain yield. Contrast test procedures were used to compare treatment means. The analyses of soil moisture data were done following conversion of soil moisture potential to volumetric moisture

P. W.. Chirwa / Forest Ecology and Management 64 (I 994) 23 I- 243

237

150 Flemingia fertilized

~

100

$

%

:::t

40

F oon

60

80

,oo

80

00

aoofeozod

40

60

~ s M~ l~te~r~

Fig. 6. Dry matter production in maize Rows 1-3 and the middle maize row of the control plot in fertilized and unfertilized maize grown between flemingia hedgerows.

content (0~) using the retentivity equation after Hutson and Cass ( 1987):

Ov=O~(h/a) lib where 0s is the volumetric moisture content at saturation and a and b are constants obtained by a computer program for the best fit moisture release curve based on the soil moisture retention data of this soil.

3. Results and discussion

3.1. Maize height The first row of maize was the shortest in both fertilized and unfertilized plots. In fertilized plots, the height of the maize in the fn~st maize row was comparable with that of the sole crop of maize Figs. 2 and 3). However, in alley-cropped maize with prunings alone, plants in the middle

P. W. Chirwa / Forest Ecology and Management 64 (1994) 231-243

238

250

95 DAP 200

i

~.

15o

.~

I00

~'-? N N

b

[~>

50

F~-LiJimed

Llnfmrtttimed

Leucaena

Fmrtilimed

Ux~er[ihnmd

Flemingia

Fig. 7. Dry matter accumulation 95 DAP in fertilized and unfertilized maize rows between leucaena and flemingia hedgerows. Bar graphs in each alley with the same letter are not statistically different at P= 0.05.

row were generally shorter than corresponding ones in the sole-cropped plots. Sixty-two days after planting, the maize height in the first maize row was significantlyshorter than,that of the second and third maize rows while there were no significant differences between the second and third maize rows in maize applied with fertilizer and prunings in both leucaena and flemingia alleys, as well as in alleys with flemingia prunings alone. However, there were no significant differences among the three maize rows in plots that had leucaena prunings alone (Fig. 4).

3.2. Maize dry matter Generally, there were no differences in maize dry weight of maize plants in plots with either leucaena or flemingia. Maize plants which had both hedgerow prunings and fertilizer weighed significantly more (P<0.01) than those with hedgerow prunings alone. In leucaena alleys, the maize plants were similar in all rows in both fer-

tilized and unfertilized plots. However, in fiemingia alleys, maize plants next to the hedgerows weighed significantly (P
3.3. Maize grain yield In alleys of leucaena and fiemingia, maize plants with hedgerow prunings and fertilizer

P. W. Chir~a / Forest Ecology and Management 64 (1994) 231-243

239

3.5 FO U n I e r U l ~ . e d

3.0 2.5

2.0 • --

...,

....

"x'x'

.~_ "1,0 g 4 1 "" e~, 0.5

0.0

FerLili~ed

U n f c ~ t ~ i 1 ~ d

FectRized

UnfertAli~ed

Flemingia Fig. 8. Grain yieldin fertilizedand unfertilizedmaizerowsbetweenleucaenaand flemingiahedgerows.Bargraphsin eachalley with the sameletterare not differentstatisticallyat P= 0.05. showed no differences in grain yield, nor were there differences between them and fertilized maize grown as a sole crop in the 1989/1990 season. The fertilized maize in alleys produced more than twice as much ( P < 0.01 ) grain as the unfertilized alleys in the alleys of both hedgerow species. The first maize row produced significantly lower ( P < 0.01 ) grain than the second and third maize rows in flemingia alleys, while in leucaena alleys there were no differences in grain yield among the maize rows (Fig. 8). The maize rows next to the hedgerows in fertilized leucaena alleys produced more ( P < 0 . 0 2 ) grain yield than corresponding maize rows in flemingia alleys. In flemingia alleys, the maize with hedgerow prunings alone produced one and a half times (P<0.05) more grain than that in leucaena alleys. Leucaena and,flemingia hedgerows equally reduced the grain yields of adjacent maize rows while the second and third maize rows in flemingia alleys produced significantly more (P<0.01)

grain than corresponding maize rows in leucaena alleys. Maize with flemingia prunings alone produced significantly more (P<0.05) grain than an unfertilized sole crop of maize, while maize with leucaena prunings alone produced yields lower than that of the unfertilized maize grown as a sole crop. Where urea is applied to maize together with hedgerow prunings, the r e a d y available urea may have been a more effective source of nitrogen compared with prunings which take some time before they are decomposed and subsequently mineralized. The effect of prunings as a nutrient source was not even evident when prunings were considered as a nitrogen source in the absence of the inorganic fertilizer. For example, leucaena hedgerows produced approximately 4.2 t h a - ~dry weight compared with 2. ! t h a - ~produced by flemingia hedgerows. Assuming nitrogen percentages of 3.4 and 3.2 from leucaena and flemingia, respectively (Yamoah et al., 1986),

P. W. Chirwa / Forest Ecology and Management 64 (1994) 231-243

240

70

Leuoaena 60-

a.

=

Hedgerow

t"

Row 1

o

Row 2 Row 3

40-

20-

10-

10

30

50

70

B

0.;32 t 0.301

~ 0.20 .~ 0.24

-

0.20 o

!:o=l I Phase 1 Phase 2 Phase ;3 Days After Planting (DAP)

Fig. 9. Soil suction (A) and moisture content (B) c;.anges at 15 cm depth during the maize growing season under a leucaena alley.

leucaena prunings could have supplied 143 kg ha-i of nitrogen compared with 71.4 kg ha-i from flemingia prunings. Despite this marked difference, unfertilized maize with flemingia prunings alone produced more grain than unfertilized maize with leucaena prunings alone. It therefore seemed that not all the nitrogen from prunings was available to the maize plants. Availability of nitrogen from leucaena prunings to the current season's crop has been reported to

range from as low as 9.4% to as high as 65% (Guevara, 1976; Brewbaker and Evensen, 1984; Mulongoy and Van-der Meersch, 1988). With flemingia mulch decomposing more slowly than leucaena mulch (Budelman, 1988), nitrogen availability will be even less compared with leucaena. Some of the nitrogen from prunings is lost through volatilization especially when prunings are applied as mulch (Brewbaker and Evensen, 1984). In this study, the second application of

P. IV.. Chirwa / Forest Ecolosy and Management 64 (1994) 231-243

241

60

= Hedgerow Flerningia 50-

4O

A

Row,

: :°°;; ~ /

]

~

2o ¸

10-

O'Ol lO 0.32.

~i 0.28 0.24 == Hodgoro

~

v I

o~o1" .owe II 10

30 Phase 1

50 Phase2

I1~~

70 Phase3

" ~

~

90

DaysAfterPlanting(DAP)

Fig. 10.Soilsuction(A) and moisturecontent (B) changesat 15cmdepthduringthe maizegrowingseasonundera flemingia alley. prunings was as mulch that would not have decomposed and provided nitrogen to the current season's crop. Thus, crop yield can not be considered to have been influenced by nitrogen contribution from the prunings applied as mulch.

3.4. Soil moisture In both leucaena and flemingia alleys, the moisture content was essentially the same under

hedgerows and maize rows until 30 DAP (Figs. 9 and 10). Thereafter, moisture content was higher under hedgerows than under maize rows. However, the moisture content tl~roughunt the period of monitoring was similar under the n~ize rows in alleys of both leucaena and flemingia. The moisture potential (as suction) and soil moisture content changes during the maize growing season in the alleys were used to determine the occurrence of drying phc~ses. Three

242

P.W. Chirwa /Forest Ecology and Management 64 (1994) 231-243

Table2 The analysesof variancefor moisturedepletionin phases l and 3 Phase

Depth/source

Species

Row

i

0-15 15-30 0-15 15-30

NS NS NS NS

NS NS * NS

3

The symbols* and NS denotesignificanceat a=0.01 and non-significance,respectively. drying phases were identified: the first (28-31 DAP), the second (47-50 DAP) and the third (63-66 DAP). Hydraulic gradient values were used to determine the flow direction of moisture (Reeve, 1986) in the 15-30 and 30-45 cm zones in each phase. The moisture flow in the 0-45 cm zone was generally upwards in the first and third phases in both leucaena and fiemingia alleys. This upward flow of moisture was attributed to evapotranspiration by both maize plants and hedgerows. However, in the second phase, the moisture flow was downwards which may have been a result of drainage as this phase was preceded by heavy rainfall. It was impossible, therefore, to separate the moisture depletion that was due to evapotranspiration and that which was due to drainage. Hence, this discussion only considers the moisture depletion in the first and third phases. Table 2 shows the analysis of variance for soil moisture depletion in the phases considered. In the firstphase, there were no differences in moisture depletion between leucaena and flemingia plots, among the three maize rows in both 0-I 5 and 15-30 c m depths in alleys of both leucaena and flemingia, and in moisture depletion between hedgerows and maize rows in all treatment alleys.However, in the third phase, hedgerows in both leucaena and flemingia alleys depleted the soil to a significantly lower (P<0.01) moisture than the maize rows in the 0-15 cm depths (Figs. 9 and I0). Maize plants were only 4 weeks old in the first depletion phase and would therefore not be taking large amounts of water from the soil.In ad-

dition, the hedgerows had been pruned 2 weeks before planting which reduced the surface area for evapotranspiration. However, the upward moisture flow in the first phase under both leucaena and fiemingia alleys implies that most of the moisture depletion was by direct evaporation rather than transpiration. The significantly lower moisture depletion under the hedgerows implies that they were not competing for moisture with maize rows. Although there were no differences in soil moisture utilization under the three maize rows, the first maize rows produced significantlylower dry matter than the other rows which would imply a lower water use efficiency in the former maize row. Also, the generally higher moisture content under the hedgerows than under the maize rows implies that the extra water under the first maize row was mostly utilized by the second and third maize rows. In addition, the northsouth orientation of the hedgerows meant that shading of the first maize rows by hedgerows may also have affected dry matter accumulation at the time when plants were below 50 cm, the pruning height of the hedgerows. The grain yield in the 1989/1990 season was lower than that in the 1988/1989 season. This reduction in yield may be attributed to higher rainfall in the 1988/1989 season which was 39% above average for the station compared with 12% below average in the 1989/1990 season. In addition, moisture stress started at about silking time (65 DAP) until harvest time in 1989/1990 (Figs. 9 and 10). Soil moisture potential in the 0-5 cm zone had decreased below - 4 0 KPa under the maize rows and this has been reported to cause moisture stress to maize plants (Quisenberry, 1988). Singh et al. (1989) also reported great yield reduction in alley-cropped cowpea, sorghum and castor when the rainfall was 30% below average at the site. 4. Conclusions Although leucaena prunings produced more dry matter than fiemingia, the nutrients contained may not be immediately available to the

p. w.. Chirwa/ ForestEcologyand Management 64 (1994) 231-243

m a i z e crop. Low d e c o m p o s i t i o n rates o f flemingia leaves m a k e t h e m very effective as mulch. This mulching effect m a y b e m o r e crucial for conserving moisture during d r y conditions, as seems to have been the case t o w a r d s the e n d o f the growing season during this study. Flemingia hedgerows could have competed for moisture with the first maize row which m a y have resulted in low d r y m a t t e r a n d grain yield in this row. T h e i m p r o v e m e n t o f the microsite b y the dense litter layer o f leucaena m a y be the reason for no significant differences in d r y m a t t e r a n d grain yields in leucaena alleys. T h e study showed t h a t u n d e r d r y a n d low fertility conditions, flemingia was a better hedgerow species than leucaena; but when fertilizer was added, there were no differences between the two species.

5. Acknowledgement D u r i n g the p e r i o d o f the study, P.W. Chirwa was on leave o f absence from the Malawi G o v ernment, D e p a r t m e n t o f Forestry., on a scholarship a w a r d e d by the International Council for Research in Agroforestry ( I C R A F ) , N a i r o b i , Kenya.

6. References Brewbaker, J.L. and Evensen, C.L.I., 1984. Leucaenn; Promising Foliage and Tree Crop for the Tropics, 2nd edn. National Research Council, National Academy Press, Washington DC. Budelman, A., 1983. The decomposition of the leaf mulches of Leucaena leucocephala, Gliricidia sepium and Flemingia macrophylla under humid tropical conditions. Agrofor. Syst., 7( 1): 33-45. Guevara, A.B., 1976. Management ofLeucaena leucocephala (Lain. de Wit) for maximum yield and nitrogen contribution to intercropped corn. PhD Dissertation, University of Hawaii, USA. Hutson, J.L. and Cass, A., 1987. A retentivity function for use in soil water simulation models. J. Soil Sci., 38: 105113.

243

Kamara, C.S. and Ma~kc, S., 1989. An ovcrvi~ of SADDC/ICRAF zonal aarofo~try projca at C l ~ i ~ bana. First Zambian National Agrofores~ryW o r ~ . Kang, B.T. and Wilson, G.F., 1987. The d c ' v e ~ e n t o f ~ cropping as a promising agroforestry technoh3gy.In: H.A. Steppler, and P.ICR. Nair (Editors), Agrofore~ry: A Decade of Development. Internation~ Council for Research in Agroforestry, Nairobi, pp. 227-243. Kang, B.T., Wilson, G.F. and Spikens, L., 1981. Alley crop~'ag maize (Zea mays) and Leucaena [eucoccpha~ (Lam.) in Southern Nigeria. Plant Soft, 63: 165-179. Kang, B.T., Grimme, H. and Lawson, T.L., 1985. Alleycropping sequentially cropped maize and cowpea with Leucaena on a sandy soil in southern Nigeria. Plant SOil,85: 267-277. Lal, R., 1974. Soil temperature, soil moisture and maize yield from mulched and unmulched tropical soils. Plant Soil, 40: 129-143. Lal, R., 1989. Agroforestry systems and surface soil management of a tropical alfisol. Part II, Water run-off, soil erosion and nutrient loss. Agrofor. Syst., 8(2): 97-111. Marthaler, H.P., Vogelsagcr,W., Richard, F. and Wierenga, P.J., 1983. A pressure transducer for field tensiometers. Soil Sei. SOc.Am. J., 47: 624-627. Mulongoy, K. and van der Meersch, M.K., 1988. Nitro$en contribution by Leucaenaleucocephalaprunings to maize in an alley cropping system. Biol. Fertil. Soils, 6(4): 282285. Nalr, P.K.R., 1990. The Prospects for Agroforestry in the Tropics. World Bank Technical Paper No. 131, Washington, DC. Quisenberry, V.L. 1988. Sehedulin8 irrigation for corn in the South East, Blackville,South Carolina. United States Department of Agriculture, Agricultural Research Service, ARS-65. Reeve, R.C., 1986. Water potential: piezometry. In: A. Klute (Editor), Methods of Soil Analysis. Part I. Physical and MineralogicalMethods. AgronomyMonographNo. 9, 2nd ed. American Society of Agronomy, Madison, WI, pp. 545-562. Singh, R.P., Ong, C.K. and Saharan, N., 1989. Above and below ground interaction in alley cropping in semi-arid India. Agrofor. Syst., 9: 259-274. Ssekabembe, C.K., 1985. Perspectives on hedgerow intercropping. Agrofor. Syst., 3: 339-356. Yager, "I.U., Lee, C.A. and Perfect, G.A., 1967. Det~led Soil Survey and Irrigability Classification of the Chalimbana Area, Zambia. Government Printer, Lusaka. Yamoah, C.E, Agboola, A.A. and Wilson, C.F., 1986. Nutrient contribution and maize performance in alley cropping systems. Agrofor. Syst., 4: 247-254.