African Crop Science Journal African Crop Science Society ISSN: 1021-9730 EISSN: 2072-6589 Vol. 7, Num. 4, 1999, pp. 585-590

African Crop Science Journal, Vol. 7. No. 4,  pp. 585-590, 1999                                                          

Economic analysis of maize-bean production using a soil fertility replenishment product (prep-pac) in Western Kenya

P. NEKESA, H. K. MARITIM, J. R. OKALEBO and P. L. WOOMER¹
Faculty of Agriculture, Moi University, P.O Box 1125, Eldoret, Kenya
¹Department of Soil Science, University of Nairobi, P.O Box 29053, Nairobi, Kenya

Code Number: CS99049

 ABSTRACT 

The Phosphate Rock Evaluation Project (PREP) is testing PREP-PAC, a soil fertility replenishment product specifically designed to ameliorate nutrient-depleted "patches" symptomatic of the worst maize-bean intercrops of smallholders’ fields in western Kenya. PREP-PAC contains two kg Minjingu rock phosphate, 0.2 kg urea, legume seed, rhizobial seed inoculant, seed adhesive and lime pellet, is assembled and is sold  for Ksh. 42  (US $ 0.76) and is intended for 25 m² areas. PREP-PAC was tested on 52 farms in four districts of western Kenya during 1998 and compared with adjacent control plots.  Farmers selected either a local bush or climbing variety (cv. Flora) of Phaseolus vulgaris  as an intercrop with maize (Zea mays). Use of the combined PREP-PAC and climbing bean package increased maize and bean yields by 0.72 and 0.25 t ha^-1, respectively (P < 0.001), resulting in a 161% return on investment.  Total revenue from low pH soils (<5.2) was Ksh. 25  for the control and Ksh. 47 for PREP-PAC. In moderate soil pH  >(5.3), total revenue was Ksh. 31 for control and Ksh. 68 for PREP-PAC (P < 0.05). Opportunity exists to distribute an affordable soil fertility restoration package among smallhold farmers but the profitability from its use is dependent upon soil conditions and accompanying legume intercrops.

Key Words: East African Highlands, nutrient-depleted soil, nutrient replenishment,  smallholder farming systems, rock phosphate

RÉSUMÉ

Le projet d’évaluation de la roche de phosphate est entrain de tester  un produit de restauration (PREP-PAC) de la fertilité du sol, particulièrement désigné pour améliorer des parcelles épuisées d’élements nutritifs,  poche   symptômatique des champs de mauvaises association maïs-haricots chez les petits fermiers dans l’Ouest du Kenya.  PREP-PAC contient deux kg de roche de phosphate de Minjingu, 0.2 kg d’urée, semence de légume, semence rhizobiale inoculante, semence adhésive et pelote de chaux, est assemblée et commandée à 42 K shs (US$ 0.76) pour une superfice de 25 m².  Le produit a été testé sur 52 champs dans 4 districts de l’Ouest du Kenya en 1998 et a été comparé avec les parcelles temoins adjacents.  Les agriculteurs ont choisi entre une variété volubile et/ou courte de haricot (Phaseolus vulgaris) comme culture d’association avec la maïs (Zea maïs).   L’utilisation du PREP-PAC combiné avec le haricot volubile a augmenté les rendements du maïs et du haricot de 0.72 et 0.25 t ha^-1 respectivement (P<0.01), aboutissant à 161% de profit sur l’investissement.  Le revenu total de sol au pH bas  (<5.2)  a été 25 Ksh pour la parcelle temoin et 47 Kshs pour PREP-PAC. Dans les sols modérés (>5.3), le revenu total a été Ksh 31 pour le temoin et Ksh 68 pour PREP-PAC (P<0.05).  Opportunité existe pour offrir un paquet abordable de restoration de la fertilité du sol chez les fermiers mais leur rentabilité dependra des conditions de sols et de légumes accompagnant l’association.

Mots Clés: Haute terres de l’Afrique de l’Est, soil épuisé d’élément nutritifs, restauration des nutritifs, petits  agriculteurs, roche de phosphate

Introduction

Farmers in western Kenya produce crops under diverse biophysical and socioeconomic conditions.  Maize intercropped with beans are the main crops produced for household food consumption with occasional surpluses sold for cash. Recent studies indicate that maize and bean fields are being mined of plant nutrients resulting from an imbalance between nutrient inputs and losses (Sanchez, 1997). Every cropping season, plant nutrients are withdrawn from the soil through crop harvests and soil erosion at higher rates than they are replaced through fertiliser and organic matter applications (Woomer et al., 1998). This steady depletion poses a serious threat to the welfare of smallhold farmers in western Kenya. Persistent nutrient imbalances over many seasons results in nutrient depleted "patches" in the maize-bean fields.  These fertility-depleted patches persist because farmers have little opportunity to reverse this trend due to poor access to markets and restricted availability of modern farm inputs (Woomer et al., 1998). In conjunction with CARE International and Siaya Community-Oriented Development Project, the Phosphate Rock Evaluation Project (PREP) combined fertiliser and germplasm technologies intended for use in western Kenya (Table 1). The PREP-PAC is formulated to restore fertility to 25-50 m² of nutrient depleted acid soils. It contains Tanzanian rock phosphate (2 kg), urea (0.2 kg) legume seed and BIOFIX rhizobial inoculant and is assembled at a cost of Ksh 37.20 (US $ 0.67)

Table 1. Formulation and assembly costs of PREP-PAC, a nutrient replenishment product under development for use by smallhold farmers in western Kenya

1US$ = 70 Ksh.

Development and distribution of these packages is an example of how regional resources may be better mobilised to address local problems. The objective of this study was to determine the economic returns from PREP-PAC application in fertility depleted maize-bean patches of western Kenya.

Methodology

Study area. PREP-PAC was tested on 52 representative farms of smallhold maize-based systems of the highland parts of Bungoma, Kakamega, Siaya and Vihiga districts. Farm sizes vary between 0.5 and 2.0 ha, with a median of 1.2 ha (David and Swinkels, 1994). Average maize yields in farmers’ fields range from about 0.4 to 2.0 t ha^-1 season^-1 (Jama et al., 1997). Soils at the experimental sites had generally low fertility (Table 2), and farmers considered these the most fertility-depleted areas of their farms. These sites were characterised by nutrient deficiencies often expressed as stunted, yellow and/or purple maize plants.

Table 2. Selected soil chemical properties for the 52 on-farm experimental locations

Experimental design and management. The test input, PREP-PAC, was provided to farmers and recommended application procedures  explained. All farm operations, including application,  planting density, weeding intensity,  pest and disease management were performed by  participating farmers. Two adjacent plots each measuring 5 m x 5 m were marked and treatments applied.

In the PREP-PAC treatment, rock phosphate and urea were evenly spread then incorporated into the soil to a 15 cm depth, inoculated bean seed and maize were immediately sown. The control plot had beans and maize intercropped without addition of external nutrient sources. 

Treatments were designed to compare economic returns to PREP-PAC with no fertility amendment practices in the maize-bean intercrops. In both treatments, farmers planted the same maize variety of their choice, and either climbing (cv. Flora) or local bush variety of Phaseolus vulgaris contained in the PREP-PAC. Treatments on each experimental site were subjected to the same management practices determined by the individual farmer. After harvest, sun-dried  maize grain and bean seed from the two plots were weighed.

Economic analysis. Economic returns to PREP-PAC were assessed in terms of yield, gross field benefits and returns to investment. Costs and benefits of each treatment were compared using a partial budgeting model which included only costs and benefits that varied from the control (i.e., costs of PREP-PAC and the increased maize and bean yield)  (CIMMYT, 1988). Costs such as ploughing and weeding that did not differ between treatments were ignored for the purpose of this analysis.  The cost of PREP-PAC use by the farmer was Ksh 42 (assembly cost of Ksh 37 plus Ksh 5  application labour cost).  The average field price for maize and beans during the harvesting season of 1998 was Ksh 10 and Ksh 23 per kilogram,  respectively. Net benefits from PREP-PAC use was calculated by subtracting the cost of PREP-PAC use from the gross field benefits (the added value of maize and beans). Crop yields and net benefits were compared between low soil pH (<5.2)  and moderate soil pH ( >5.3) because effective dissolution of rock phosphate to release soluble P may differ at soil pH 5.3 and below (Buresh et al.,  1997). 

Results

Grain yield. Maize grain yields were lowest in unfertilised treatments under the two pH regimes with an overall mean of 0.64 t ha^-1. PREP-PAC application increased maize yield to 1.36 t ha^-1 (Fig.1).

The highest maize yield was at soil pH >5.3 with a mean of 1.67 t ha^-1. There was almost total crop failure for unfertilised bush beans at soil  pH  <5.2, yielding only 0.025 t ha^-1. PREP-PAC application at soil pH <5.2 improved bush bean yield to 0.125 t ha^-1. At soil pH  <5.2, climbing bean (cv. Flora) yielded 0.2 t ha^-1 and PREP-PAC application increased the yields to 0.35 t ha^-1. Flora had the highest yield of 0.45 t ha^-1 under PREP-PAC application and soil pH >5.3.  Maize intercropped with Flora bean and treated with PREP-PAC at soil pH <5.2 yielded 1.5 t ha^-1 compared with 1.2 t ha^-1 of maize under bush bean intercrop. Maize intercropped with bush bean and without  PREP-PAC  at  pH >5.3  yielded 0.75  t ha^-1 while  with  Flora  the maize yield  was 0.5 t  ha^-1.

Gross field benefits. The gross field benefits for PREP-PAC use was determined for the 25 m² experimental plots (Fig.2).  Gross field benefit for PREP-PAC use was maximum at soil pH >5.3 amounting to Ksh 68, resulting in net benefits of Ksh 26. Gross field benefits from low pH soils (<5.2) was Ksh. 25 for the control and Ksh. 47 for PREP-PAC. In moderate soil pH (>5.3), gross field benefit was Ksh. 31 for the control and Ksh. 68 for PREP-PAC (P < 0.05).

Returns on investment. Use of PREP-PAC in soil pH <5.2 increased financial return on land from Ksh 8,720 to Ksh 17,920 ha^-1, with a return ratio to PREP-PAC of  1.27 (Table 3.), thus for every shilling spend on PREP-PAC the farmer received the shilling invested plus 0.27 shillings. In moderate pH soils (>5.3), PREP-PAC use increased financial returns on land from Ksh 12, 400 to Ksh 27, 240 ha^-1 with a return ratio to PREP-PAC of Ksh 1.61.

Table 3. Returns on investment from PREP-PAC at low and moderate soil pH

¹not applicable

Discussion

The benefit of PREP-PAC application is highlighted by the dramatic response of maize and bean yield despite their low yield potential in acid soils. Economic analysis of both treatments showed that, despite the extra costs associated with PREP-PAC use, there was financial gain resulting from PREP-PAC in both soil pH regimes. Out of the 52 farms studied, 28 of them had moderate soil pH (>5.3), therefore PREP-PAC substantially improved yields on 54% of the fertility depleted soils.  Gross field benefits differed markedly between low and moderate soil pH with PREP-PAC application. A factor other than P and N apparently limited maize and bean yield response to PREP-PAC at soil pH <5.2. At pH <5.2, phosphate ions coming from rock phosphate dissolution are removed from the soil solution and sorbed by Fe and Al oxides and hydroxides (Sanchez et al., 1997). These sorbed phosphate ions are unavailable to plants in the short run, and this may explain the lower response to PREP-PAC observed at low soil pH. However, the sorbed phosphate ions are slowly desorbed and released to the soil solution during a period of several years (Sanchez et al., 1997). At soil pH 5.2 and below, Al is fairly soluble thereby causing aluminium toxicity to crops . Aluminium toxicity reduces PREP-PAC’s effectiveness at low pH implying that PREP-PAC does not have a strong liming effect that can reduce aluminium toxicity in the first season.  Low bush bean  yield (25  kg  ha^-1) in acid soils pH (<5.2) may be related to the importance of soil fertility in pest and disease management.  Nderitu et al. (1997) noted that bean stem maggot and bean root rot are greater constraints to bean production in low soil fertility. Nutrient application enhances tolerance of beans to bean stem maggot and bean root rot because a bean crop supplied with nutrients grows vigorously and is able to tolerate bean stem maggot and bean root rot attack (Otsyula et al., 1998). Therefore,  PREP-PAC application may offer an opportunity to address  two important biotic constraints to bean production in fertility depleted soils.

Conclusion

It is important to note that PREP-PAC is primarily intended as a nutrient replenishment mechanism (Sanchez et al., 1997) through market distribution (Woomer et al., 1998).  The economic returns realised during the season where PREP-PAC was applied was significant but not spectacular.  However, the phosphorus applied through PREP-PAC is sufficient to replace 10 to 30 years of nutrient loss (Sanchez et al., 1997) and returns during following cropping seasons are anticipated.  One important future development is the reduction of costs that may be possible by purchasing the package's components in bulk and through gaining greater efficiency in its assembly.

Acknowledgements

We thank Joseph Agunda of CARE-Kenya in Siaya, Dismus Okello of SCODP, Eusebius Mukhwana of SACRED Africa and Anthony Okoti of ABLH for distributing and training farmers on PREP-PAC use.  Joan Wesonga assisted in soil analysis.  Fifty two farmers of western Kenya generously assisted in the installation and management of the on-farm experiments.   We thank the Rockefeller Foundation's Forum for Agricultural Resource Husbandry for financial support that made this work possible.

References

Buresh, R.J., Smithson,  P.C.  and Hellums, D.T.  1997. Building soil phosphorus capital  in Africa. In: Replenishing Soil Fertility in Africa. Buresh, R.J., Sanchez, P.A. and Calhoun, F. (Eds.), pp. 111-149.   SSSA. Special Publication Number  51. SSSA, Madison, WI.

CIMMYT, 1988. From Agronomic Data to Farmer Recommendations: An Economic Training Manual. pp. 1-79.  Completely revised edition. CIMMYT, Mexico, D.F

David, S. and Swinkles, R.A. 1994. Socio-Economic Characteristics  of Households Engaged in Agroforestry Technology in Western Kenya. AFRENA Report. 78.  International Centre for Research in Agroforestry. Nairobi, Kenya.

Jama, B. R., Swinkles, A. and Buresh,  R.J. 1997.  Agronomic and economic evaluation of organic and inorganic sources of phosphorus in western Kenya. Agronomy Journal 89:  597-604.  

Nderitu, J.H., Buruchara, R.A. and  Ampofo, J.K.O. 1997. Relationships between bean stem maggot, bean root rots and soil fertility. The African Highlands  Initiative. Technical Report Series 4:1-16.

Otsyula, R.M., Nderitu, J.H. and Buruchara, R.A. 1998.  Interaction between bean stem maggot, bean root rot and soil fertility.  In: Second Biennial Crop Protection Proceedings. Farrel, G. and Kibata, G.N. (Eds.), pp. 70-77.   National Agricultural Research Project II. 

Sanchez, P.A., Shephered, K.D., Soule, M.J., Place,  F.M.,  Buresh, R.J., Izac, A.M. N.,  Mukwunye, A.V., Kwesiga, F.R., Nderitu, C.G. and Woomer, P.L.  1997.  Soil fertility replenishment in Africa: An investment in natural resource capital. In:  Replenishing Soil Fertility in Africa.  Buresh, J.R., Sanchez, P.A. and Calhoun, F. (Eds.), pp. 1-46. SSSA Special Publication. Number 51. SSSA, Madison, WI.

Woomer, P. L., Bekunda, M.A., Karanja, N.K.,   Moorehouse, T. and Okalebo, J. R. 1998. Agricultural resource management by smallhold farmers in East Africa.  Nature and Resources 34:22-33

©1999, African Crop Science Society

The following images related to this document are available:

Photo images