John Mukalama

Optimising crop productivity in legume-cereal rotations through nitrogen and phosphorus management in western Kenya

Combined application of organic resources and mineral inputs is integral to sustainable soil fertility management but in-situ production of adequate organic matter is often limited by P availability. An experiment was set up at Nyabeda in Western Kenya aimed at (1) quantifying the contribution of herbaceous and grain legumes to nitrogen supply in a cereal-legume rotation system and (2) quantifying the impact of targeting phosphorus (P) to certain phases of the rotation on overall maize grain yield. In this split-split plot experiment, Mucuna pruriens was used as the herbaceous legume while soybean was used as the grain legume. Results obtained in the two seasons of the study indicated that the use of either mucuna or soybean as previous crop significantly increased maize grain yield with or without the addition of nitrogen fertilizer. More than 5 tons ha-1 of maize grain yield was realised in season two following the addition of phosphorus fertilizer at both season one and season two compared to about 3 tons ha-1 of maize grain yields obtained when no P was added. It could be concluded that in this region, the addition of P fertilizer is an integral management option to ensure optimal utilization of the nitrogen fixed by the legume crop. Using P during the legume season may be sufficient to supply P requirements to the succeeding cereal crop. Also, applying P to the mucuna or soybean legume crop was not any different from applying it both to the legume and cereal crops indicating that farmers can save labour and cash by applying P only to the legume. The good performance of maize planted after mucuna was an indication that mucuna could be used by farmers in the region as an N source (Nitrogen Fertilizer Equivalency (NFE) >100 kg N ha-1) thus reducing cost of buying N fertilizers. Although soybean showed a lower NFE of 40 kg N ha-1, it had higher economic benefits and could thus be more acceptable to the farmers. These findings could be confirmed by using more than two cereals and legume rotation cycles

Crop and Soil Response to Tillage and Crop Residue Application in a Tropical Ferralsol in Sub-humid Western Kenya

Conservation agriculture (CA) offers an opportunity to reverse prevailing land degradation and consequent loss of productivity often occasioned by intensive soil tillage in cropping systems in most parts of sub-Saharan Africa (SSA). A long term experiment was established in Nyabeda Western Kenya in 2003 to evaluate the effect of tillage and crop residue application on maize and soybean yields, and on soil properties. The experiment was set up as a split-split-split plot design with four replicates and involved a factorial combination of tillage system (reduced and conventional tillage), cropping system (continuous cereal, soybean-maize rotation and intercropping), crop residue – maize stover – management (plus and minus crop residue) and nitrogen (N) application. Results showed that tillage influenced performance of maize although significant tillage effects were observed in only 5 out of the 15 seasons analyzed. Overall average maize grain yields were 2.9 ton ha−1 in reduced tillage and 3.6 ton ha−1 in conventional tillage systems. Application of crop residue increased seasonal maize grain yield in reduced tillage (340 kg ha−1) and in conventional tillage (240 kg ha−1), but the only significant crop residue (CR) effect was observed in season 10. Differences in maize yields between the two systems were attributed to phosphorus availability as it was demonstrated that application of crop residue in the reduced tillage resulted in better availability of P than without crop residue application.

Scaling Up Options on Integrated Soil Fertility management in Western Kenya: The Case of COSOFAP: Challenges and Opportunities

Western Kenya, a densely populated region of the country is an example of many areas in Africa where continued threat to the world’s land resources is compounded by the need to raise food production and reduce poverty. Attainment of food security is intrinsically linked with reversing agricultural stagnation, safeguarding the natural resource base, slowing population growth rates, combating the negative impacts of HIV/AIDS pandemic on the community and reducing poverty. Over the last 12 years, the World Agroforestry Centre (ICRAF) in collaboration with Kenya Agricultural Research Institute (KARI), Kenya Forestry Research Institute (KEFRI) and Tropical Soil Biology and Fertility Programme (TSBF) and with support from the Rockefeller Foundation developed several integrated soil fertility management (ISFM) options. Examples are: (i) short-duration improved fallows with leguminous nitrogen-fixing species, such as Sesbania sesban and Crotolaria grahamiana; (ii) biomass transfer of Tithonia diversifolia; (iii) dual purpose legumes like soybeans and cowpeas and iv) the combination of phosphorus fertilizers, including the reactive Minjingu phosphate rock, with the above organics and farmyard manure. These options that can increase yields of maize by 2–3 folds were tested and adopted by thousands of farmers in pilot project sites in Vihiga and Siaya Districts. Other work has been pioneered by ICIPE on Push–Pull technology, MBILI by Sacred Africa, green manuring by the Legume Research Network. Besides yield improvements, other benefits associated with improved soil fertility management strategies include striga control, fodder, wood fuel production and stakes for climbing beans. However one of the biggest challenges is to scale these initiatives to more farmers in the region.