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African Crop Science Journal
African Crop Science Society
ISSN: 1021-9730 EISSN: 2072-6589
Vol. 4, Num. 3, 1996, pp. 315-324
African Crop Science Journal, Vol. 4. No. 3, pp.
315-324, 1996 

Effect of the application of dairy cattle slurry and intercropping with cowpea on the performance of maize in

coastal lowland Kenya

J.G. Mureithi, R. S. Tayler^1 and W. Thorpe^2

Kenya Agricultural Research Institute (KARI), P. O. Box 57811, Nairobi, Kenya
^1 University of Reading, Earley Gate, P. O. Box 236, Reading, RG6 2AT, U.K.
^2 International Livestock Research Institute (ILRI), P. O. Box 30709, Nairobi, Kenya

(Received 6 April, 1996; accepted 30 August, 1996)

Code Number: CS96071
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Dairy cattle slurry is a potential source of soil nutrients for smallholder dairy farmers. A study was conducted in coastal lowland Kenya to assess how best to utilise dairy cattle slurry for maize production on the infertile coastal sandy soils. The effects of rate (55 or 110 t ha^-1), time (at planting or at tasselling) and method of slurry application (burying or spreading on the surface), and of intercropping maize with cowpea were evaluated. The study was initiated in 1989 and three years results are presented. The higher rate of slurry application generally increased maize grain and stover DM yields and increased soil OM, P, K and Ca. Yields were greater with application at planting than at tasselling and with burial rather than spreading. Planting cowpea at the same time as maize depressed maize grain yield but this effect was reversed when cowpea was planted four weeks after the maize. The LER was greater than unity in four seasons out of five indicating better land utilisation under intercropping.

Key Words: Maize production, Coastal lowland tropics, cowpea intercropping, soil nutrients


Les produits de l'elevage du betail est une ressource potentielle des elements nutritifs du sol pour les elevages de petites fermes. Une etude a ete menee dans la plaine du Kenya pour evaluer la meilleure possibilite d'utiliser les produits l'elevage du betail pour la production du mais dans la cote non fertile dans les sols sabloneux. Les effets du taux (55 ou 110 t par hectare), la periode (au cours de la peride de panter) et la methode d'application (enfoncer dans le sol ou epandre sur la surface du sol), et la culture du mais associee au niebe etait evaluee. L'etude a ete initiee en 1989 et les resultats ont eu lieu cours de trois annees. Le taux le plus eleve de l'application a generalement augmente le nombre de graines du mais et le rendement DM et l'augmentation en sol OM, P, K et Ca. Les rendements etaient superieurs a cause de l'application de la methode pendant la periode de planter et avec le fait d'enforcer ou enterrer les graines au lieu de le repandre sur la surface du sol. Le fait d'associer la culture du niebe avec celle du mais a deprimee le rendement des graines du mais mais cet effet etait inverse pendant la periode o le niebe etait plante quatre semaines plustard apres le mais. Le "LER" etait superieur que l'unite pendant quatre saisons sur cinq indiquant la meilleure utilisation de la terre sous le fait de planter deux plantes dans un meme champ (intercropping).

Mots Cles: Production du mais, les tropiques des c™tes de la plaine, culture mixte du niebe, elements nutritifs du sol


Agriculture in coastal lowland Kenya is dominated by infertile free draining sandy soils utilised in smallholder farming systems that use few purchased inputs (Jaetzold and Schmidt, 1983). Fewer than 10% of subsistence farmers in the region use fertilizers (Saha, H. M., Kamau, G. M. and Gathama, S. K., unpubl.), the availability of which is unreliable. This has contributed to low crop yields and to increasing degradation of farmland. For example, farmers' yield of maize (Zea mays L.), the main staple crop in the region, averages 1.2 t ha^-1 for the crop planted at the onset of the main wet season (April to May) and about half that for the short rains crop (October to December) (Muturi, 1981; Boxem et al., 1987).

In these coastal sandy soils, nitrogen is the most limiting nutrient for maize (Boxem et al., 1987). Since commercial nitrogen fertilizers are rarely used by smallholders, there is a need to evaluate cheaper sources of locally available nitrogen. Dairy cattle slurry, which is a mixture of cow-dung, urine, feed spillage and cleaning water, is a potential source. Its availability is increasing as a result of the adoption of stall-fed cattle in the smallholder sector (Maarse et al., 1990). Its application has improved the yields of maize in USA (Klausner and Guest, 1981) and Napier grass in Kenya (van der Noll and Janssen, 1982; Wouters, 1987). This study assessed how best to utilize slurry for maize production in terms of rate, time and method of application. It also investigated the effect of intercropping maize with cowpea (Vigna unguiculata L. Walp.) as a way of improving either performance of maize or overall productivity per unit area of land under maize (Willey, 1979). Cowpea is the most important grain legume in the region (Boxem et al., 1987) and is usually grown in intercropping systems with maize, cassava and tree crops (e.g. coconut, cashew nut and citrus).


Site description. The study was carried out at the Kenya Agricultural Research Institute's Regional Research Centre at Mtwapa, Coast Province, Kenya (3 degrees 56' S, 39 degrees 44' E and 15 m a.s.l.). The agro-ecological zone at the Centre is coastal lowland 3 (CL3), as described by Jaetzold and Schmidt (1983), which has a long cropping season (LCS) from April to June and an unreliable short cropping season (SCS) from October to December. The mean annual rainfall and evaporation, 1969 to 1991, are 1200 and 2000 mm, respectively. The potential evapo-transpiration is estimated to be 1470 mm (Siderius and Muchena, 1977), indicating a negative water balance. Mean monthly minimum and maximum temperatures are 22 C and 30 C, respectively, covering the same period. Soils have a pH-H2O of about 6.9, are moderately well drained, sandy clay to clay with sandy surface, classified as Orthic Ferralsols/Ferric Acrisols (Batjes, 1980). These soils are characterised by very low levels of macro-nutrients, especially nitrogen and phosphorus, low organic matter, low cation exchange capacity and are prone to erosion. However, soils at the experimental site were moderately high in organic matter (1.6%), nitrogen (0.06%) and other macro-nutrients because the land had been fallow for about six years.

Treatments and design were as follows:

Factorial slurry treatments

Rate of slurry application (R)
- 55 or 110 t ha^-1

Time of slurry application (T)
- At planting of maize
- When maize is about to tassel

Method of slurry application (M)
- Spread or buried

Non-factorial treatments (all without slurry)

- Sole maize without any inputs - control treatment
- Intercropping maize withe cowpea
- Cowpea maize intercrop
- Maize sown with 75 kg N and 20 kg P ha^-1 (recommended rates)

A randomised complete block design was used. Slurry treatments were combined in a factorial arrangement replicated three times, to give a total of 36 plots. The plot size was 7 x 5 m and the net plot size where data were collected was 5 x 2.25 m.

Planting and general management. Certified maize seeds were planted. In the first year the variety Coast Composite was planted, but in subsequent years it was replaced with a hybrid variety, Pwani hybrid II, because Coast Composite lacked uniformity in height and maturity. Maize seeds were planted at a spacing of 1 x 0.25 m, one seed per hill, which gave a population density of 40,000 plants ha^-1. The cowpea variety planted in this study was Katumani 80, a grain type. Cowpea seeds were sown between maize rows, two per hill at an intra-row spacing of 30 cm giving a cowpea population of about 67,000 ha^-1. They were not inoculated. Cowpea seeds were planted at the same time as the maize except during 1991 LCS when they were planted four weeks after. This was done to avoid competition because the growth of the cowpea plants was more vigorous than that of maize, and they entwined and climbed on the maize stalks. Harvesting of the cowpea began approximately two weeks before maize was ready for harvesting and continued for two weeks after harvesting of maize. Both cowpea and maize stover were cut about 3-5 cm above ground.

Slurry was either buried in about 10 cm deep furrow or spread in the inter-row spaces between maize rows. The dry matter (DM) and nutrient content of slurry applied in 1990 and 1991 are shown in Table 1; slurry analyses were not available in 1989.

Stalk borer (Chilo spp.), a common pest of maize, was controlled by application of Trichlorophon 2.5% (Dipterex) in granular form at the rate of 3.5 kg ha^-1 two weeks after germination. It was repeated every two to three weeks depending on the level of infestation. Cowpea was sprayed against leaf defoliators with endosulfan 35% EC (Thiodan) at the rate of 2.5 l ha^-1. Spraying began as early as one week after germination and was repeated every two to three weeks.

Soil and statistical analysis. Baseline and subsequent soil samples were taken at 0 - 20 cm depth and analysed at the International Livestock Centre of Africa (ILCA) and Kenya Agricultural Research Institute (KARI) laboratories for pH-H2O, organic matter, nitrogen, phosphorus, calcium and potassium. The analytical method used for the analysis of (a) organic matter was the Walkley-Black method, (b) nitrogen was the Kjeltic system with tecator block digester and distillation unit, (c) phosphorus was Bray II using Baush Lamb spectronic 20 electrophotometer, and (d) potassium and calcium was ammonium acetate neutral solution extraction using Perkin Elmer atomic absorption spectrophotometer.

Grain yields of maize and cowpea and DM yields of maize stover were subjected to analysis of variance (ANOVA) using the general linear model (GLM) procedures of the Statistical Analysis System package (SAS, 1985). Maize and cowpea grain yields were reported as grain weight (GW) at 15% moisture content (MC).


Results are presented for five maize crops from 1989 to 1991. The overall mean yields of grain and stover DM were 2.6 and 2.7 t ha^-1, respectively. During the short cropping season of 1990, the performance of the maize crop was affected by low and poorly distributed rainfall (Fig. 1). The long season crop in 1991 was affected by waterlogging due to exceptionally high rainfall in the early part of the season. Treatment interactions were not significant in the first three maize crops, but they were in the last two maize crops.

Effect of slurry treatments, 1989 LCS and SCS. Slurry treatments did not have significant (P>0.05) effect on maize grain yield during the first cropping year. The average yields were 4.6 and 3.6 t ha^-1 for LCS and SCS, respectively. However, the maize stover yield was significantly affected by rate of slurry application in both seasons and by time of application in SCS (Table 2). Doubling the rate of slurry application from 55 to 110 t ha^-1 significantly (P<0.05) increased yields by about 21% in both seasons while slurry applied at planting in the SCS significantly (P<0.01) increased stover DM yield by 35% .

1990 LCS and SCS. Rate and time of slurry application did not significantly (P>0.05) affect maize grain and stover DM yield in the LCS. In the SCS, however, the two treatments had a significant (P<0.05) interactive effect on maize grain yield (Table 3). The main cause of this interaction was that whereas applying slurry at the rate of 110 t ha^-1 during planting did not have any effect on maize grain yield, applying the same rate at tasselling increased yield by 156%. In the same season maize stover DM yield was 3.3 t ha^-1 when slurry was applied at the rate of 110 t ha^-1 which was 22% more than when slurry was applied at the rate of 55 t ha^-1. Application of slurry at planting gave 3.3 t ha^-1 of stover DM which was significantly (P<0.01) greater by 18% than when applied at tasselling. Method of slurry application significantly affected yields in the LCS but not in the SCS. In the LCS burying slurry produced 3.9 and 4.3 t ha^- 1 of maize grain and stover DM which were 39 and 34%, respectively, greater than when slurry was spread.

1991 LCS. In this season rate of slurry application significantly affected maize yields. Application at the rate of 110 t ha^-1 gave 2.6 t ha^-1 of maize grain yield which was significantly (P<0.01) greater by 44% than applying at the rate of 55 t ha^-1. Similarly, slurry application at 110 t ha^-1 significantly (P<0.05) gave a higher stover DM yield, 2.4 t ha^-1, which was 33% greater than applying at 55 t ha^-1.

The interaction between time and method of slurry application was significant (Table 4). The main explanation of the T x M interaction was that while methods of slurry application were not significantly different in their effect on yield when applied at tasselling, there were substantial and significant influences when applied at planting (Table 4). Burying slurry at planting increased maize grain and stover DM yield by 94 and 89%, respectively.

Effect on maize of cowpea intercropping and application of recommended rates of N and P compared to the mean effect of slurry treatments. During the first four seasons when cowpea were sown together with maize, maize grain and stover DM yields were reduced, on average by 30 and 20%, respectively (Table 5). By planting cowpea four weeks after maize in the LCS 1991 this reduction was eliminated and grain and stover DM yields of the intercropped maize were increased by 88% and 63%, respectively, relative to sole cropped maize. Except in SCS 1990, the land equivalent ratios based on grain yield were greater than unity, which indicated better land utilisation by intercropping compared to sole cropping (Table 6). Generally, slurry application gave greater maize yields than intercropping with cowpea. Similarly, applying N and P at the rates of 75 kg N and 20 kg P ha^-1, respectively, gave greater maize yields than cowpea intercropping and slurry application at the lower rate. Its effects were, however, not superior to that of slurry applied at the higher rate.

Effect of slurry treatments on soil organic matter and nutrients. Slurry application at 55 t ha^-1 treatments did not significantly affect soil fertility parameters one year after application (Table 7), However, application at 110 t ha^-1 significantly increased levels of P, K and Ca by 82, 109 and 26%, respectively. After the second year, slurry application at 110 t ha^-1 increased levels of soil OM, P, Ca and K. Burying slurry increased soil OM by 23% and K by 29% compared to surface application.


Maize grain yield did not significantly respond to slurry treatments or fertilizer application in the first cropping year (Table 5). This was apparently due to the fact that the study site was fallowed for over six years before the experiment began, and the soils were likely to have been rich in OM and soil nutrients. In subsequent seasons responses were greater, probably reflecting declining soil fertility.

Slurry application at the rate of 110 t ha^-1 generally increased maize yields, soil OM and soil nutrients, especially P, K and Ca. This is attributed to the substantial amounts of OM and nutrients returned by slurry applied at that rate (Table 1). It may not be practical to give a blanket recommendation on the rate of slurry application as this will depend on many factors; for example, the area of maize to be fertilised, slurry availability at the small holder farm and the soil fertility status of the farm. However, the rate of 55 t ha^-1 reflected more closely slurry availability at the farm level in the region. Estimates of slurry production have indicated that a hectare of Napier grass can support 3.75 livestock units (1 LU = 450 kg) and that during one year a total of about 55 tonnes of slurry can be produced (Wouters, 1987). The present study has shown a range of responses of maize yields to slurry application which may help the farmer and the extension agent to make more informed decisions on the use of slurry.

Application of slurry at planting was more effective than applying at tasselling. This can be attributed to the longer period during which the nutrients supplied by the slurry are available to the growing plants. In particular a low supply of nutrients in the early stages of growth can lead to stunted plants with poorly developed root systems. Such plants may respond less effectively to nutrients supplied at the later stages of growth, for example, when slurry is applied at tasselling. Deficiency of nutrients especially nitrogen during the early stages of maize growth (40 days from planting) has been reported to cause drastic reduction in grain yield (IITA, 1982). A major disadvantage of applying slurry at planting is the possible loss of some slurry N and other mobile nutrients by leaching (Murwira et al., 1995). There was evidence of such a loss during the SCS 1990 when heavy rains occurred at the onset of the season which may have caused leaching (Fig. 1). This is because the application of the higher rate of slurry when planting maize at the onset of the season did not increase grain yield but the same rate applied at tasselling increased yield by 156% (Table 3).

Burying slurry gave higher maize yields than spreading probably because the slurry OM decomposed more rapidly, and released nutrients into the soil. However, the soil analysis after the second year of cropping indicated that burying but not spreading slurry increased soil OM. In this case the increase in OM is probably associated with increased maize biomass production in terms of root and shoot, and not reduced rate of slurry decomposition. Another advantage of burying slurry reported elsewhere is reduced losses of nitrogen by volatilisation (Klausner and Guest, 1981; Wouters, 1987) which may have contributed to improved yields in this study.

A major limitation to burying slurry is that it requires more labour than spreading. In a study carried out on a neighbouring site, about 20 man-days were required for transportation and application of slurry to Napier grass by spreading, and 40 man-days for burying (Mureithi et al, 1995). On smallholder farms the higher maize yields achieved by burying slurry have to be balanced against the higher labour requirement of burying; labour is a major constraint to farming in the region (NDDP, 1992). A farmer near the Research Centre is halving his labour requirement for returning slurry to his Napier grass by applying it in every alternate Napier row. Synders et al. (1992) compared this method of application with the recommended one of applying in every row and they found no significant differences between the two methods. A similar study for maize production is recommended.

In addition to the demand for labour, another factor likely to limit the use of slurry in the region is the scarcity of water for cleaning the feeding stalls. The number of rural households with piped water is negligible and most families have to fetch water from outside their farms, some from great distances. To overcome these limitations some farmers prefer making compost with the cattle dung (Maarse et al., 1990). In this way little water is required to clean the stalls and the labour requirement for making compost and applying it in the field is less than for managing slurry.

In addition to the pulse grains they provide, intercropping with legumes can enhance the performance of the cereal crop by the addition of nitrogen through mineralisation of fallen leaf, dead roots and sloughed nodules and by direct addition through root exudate (Agboola and Fayemi, 1972). In this study planting cowpea at the same time as maize resulted in severe competition that reduced maize yield. In the LCS 1991, planting cowpea four weeks after maize eliminated the competition and increased maize yields substantially. However, this is the season when sole maize yield was lowest and this could have exaggerated the benefits of intercropping. In order to minimise competition, non-climbing varieties of cowpea may be more suitable (Remison, 1978). The precise intercropping management required will depend on whether yields from the cowpea (grain and leaves) are important or whether it is primarily included to enhance the yield of maize grain.


This study set out to test slurry management practises for maize production and to assess the effect of intercropping cowpea with maize. Application of slurry at the rate of 110 t ha^-1 returned substantial amounts of nutrients to the soil and gave greater maize yields. However, it is not possible from this work alone to make a general recommendation about rate of slurry application to maize. The responses obtained relate to a limited number of seasons on a single site of previously fallowed land. In any case, the appropriate rate will also depend on the availability of slurry relative to the area of maize cropping. Application of slurry at planting, following the onset of the rains, gave higher maize yields than application at tasselling although there is a danger of loss of slurry N and other mobile nutrients by leaching. Applying slurry by burying rather than spreading gave greater yields, but the labour cost for burying must be balanced against the yield advantage obtained. Use of livestock excreta as fertilizers for crop production is an important method of importing nutrients to smallholder farms through the utilisation of forages harvested outside the farms and of purchased concentrates. These results show that application of livestock litter can contribute significantly to improved productivity of smallholder mixed dairy farms.

Intercropping with cowpea increased maize yields when the cowpea seeds were sown four weeks after maize. For all the seasons the LERs were greater than one which indicated better land utilisation by intercropping. This advantage of intercropping has contributed to increased and stable food supply in subsistence farming in the tropics.


Thanks are extended to Kenya Agricultural Research Institute and International Livestock Research Institute (prior to 1994, the International Livestock Centre for Africa) for funding this study. The support of Centre Director KARI - Mtwapa is gratefully acknowledged. Assistance from KARI and ILRI field staff is greatly appreciated. Special thanks are extended to Francis Gitahi and David Njubi for assisting in data analysis.


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Boxem, H.W., de Meester, T. and Smaling, E.M.A. 1987. Soils of the Kilifi area. Kenya Soil Survey. Reconnaissance Soil Survey Report No. R11, pp 249.

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Jaetzold, R. and Schmidt, H. 1983. Farm Management Handbook of Kenya, Volume IIC. East Kenya (Eastern and Coast Provinces). Farm Management Branch, Ministry of Agriculture, Nairobi, 411pp .

Klausner, S.D. and Guest, R.W. 1981. Influence of NH3 conservation from dairy manure on the yield of corn. Agronomy Journal 73:720-723.

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Mureithi, J.G., Tayler, R.S. and Thorpe, W. 1995. Productivity of alley farming with leucaena (Leucaena leucocephala Lam. de Wit) and Napier grass (Pennisetum purpureum K. Schum) in coastal lowland Kenya. Agroforestry Systems 31:59-78.

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Muturi, S.N. (Ed.). 1981. Agricultural Research at the Coast. Report No.6. National Council for Science and Technology Kenya, 58pp.

NDDP, 1992. Results of the Farm Survey in Kilifi District. National Dairy Development Project, Monitoring and Evaluation Unit, Ministry of Agriculture, Livestock Development and Marketing, Hill Plaza, Nairobi, 23pp .

Remison, S.U. 1978. Neighbour effects between maize and cowpea at various levels of N and P. Experimental Agriculture 14:205-212.

SAS Institute Inc., 1985. SAS User's Guide: Statistics Version, 5th Edition, Cary, North Carolina pp. 956.

Siderius, W. and Muchena, F.N. 1977. Soils and environmental conditions of agricultural research stations in Kenya. Kenya Soil Survey. Miscellaneous Soil Paper No. M5, pp. 91-92.

Synders, P.J.M., Orodho, A.B. and Wouters, A.P. 1995. Effect of manure application methods on yield and quality of Napier grass. Kenya Agricultural Research Institute, NAHRC-Naivasha, 50pp.

van der Noll, I.E. and Janssen, B.H. 1982. Cow dung slurry as organic manure for fodder crops in Kilifi, Coast Province Kenya. Preliminary Report No.5. Kilifi Series Agricultural University, Wageningen, The Netherlands, 22pp .

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Wouters, A.P. 1987. The effect of the application methods of slurry on the growth and the nutritive value of Napier grass. Progress Report. National Dairy Development Project. Ministry of Livestock Development, Kenya, 12pp.

Copyright 1996 The African Crop Science Society

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