Optimising soil water and nutrients for enhancing sorghum productivity in semi-arid eastern Kenya

J.K. Itabari, P. Kathuli, E.N. Njiru, S.N. Nguluu, J.N. Maina and T.K. Mutuoki

Summary

Sorghum is the 2nd most important cereal crop in semi-arid eastern Kenya after maize. Its productivity has remained low, at 0.5 t ha–1 despite development of varieties with a yield potential of 2-5 t ha–1. In the recent past, farmers repeatedly cited lack of market opportunities as the main constraint to increased production. However, with the decision of the East African Breweries Limited to use sorghum as a source of malt in the production of beers, this constraint has been effectively eliminated (at least for those growing Gadam sorghum variety). Among the rest of the often-cited production constraints, inadequate soil water supply, low soil fertility and use of unimproved varieties are the most important. Optimising soil water use through appropriate soil water and nutrient management and use of adapted, high-yielding sorghum cultivars will increase sorghum productivity, thereby enhancing food security and incomes of the resource-poor farmers. The objectives of the project are to: i) determine the suitability of the modified mouldboard plough in soil water management, ii) determine the economic viability of using the modified mouldboard plough in sorghum production under improved soil fertility conditions, iii) create farmers’ awareness of availability of an adapted, high yielding sorghum variety (Gadam), and iv) train farmers on preparation of fortified compost.

Improving the efficiency of utilisation of phosphorus from rock phosphate through plant and biological-based interventions

E.M. Gichangi, P. Kathuli and J.M. Wambua

Summary

Low inherent soil fertility largely accounts for low crop yields on most smallholder farms in most tropical and sub-tropical soils. Soil phosphorus (P) is the least mobile and least available of the major plant nutrients. Its low availability is a major constraint to agricultural production in most soils and has been described as “the bottleneck of world hunger”. Direct application of indigenous rock phosphates has been viewed as an attractive option for building soil P fertility because it potentially involves lower production costs and capital investments than the production and use of water soluble P fertilisers. Sub-Sahara Africa has numerous phosphate rock deposits. However, most of the phosphate rocks are of igneous origin and are unsuitable for direct application due to their low solubility. Soil properties that influence the dissolution of apatite in the phosphate rocks include soil pH, CEC, Ca concentration, P sorption capacity and organic matter content among others. Certain plant species exhibit mechanisms localised in the rhizosphere that allow for the efficient use of P through dissolution of rock phosphate through excretion of organic acids with subsequent crops benefiting from the increased P availability. Similarly, soil phosphate solubility is reported to increase as the content of organic matter in the soil increases. However, there is little information in the literature on the use of plant and organic amendments-based mechanisms to enhance solubility of rock phosphates in soils under semi-arid environments. Improving solubility of these phosphates could provide resource-poor smallholder farmers with an affordable source of phosphorus for their crops. The objectives of the proposed research work are to: i) evaluate the effect of composting rock phosphate with organic manures on solubility of P from rock phosphates in selected soils of the semi-arid parts of Kenya, and ii) evaluate P benefits of different legume crops to subsequent cereal crops in different soil types.

Evaluation of the yield potential of cassava when intercropped with legumes and fertilised with NPK fertiliser under semi-arid conditions

E.M. Gichangi, J.M. Wambua, D. Mutisya, J.W. Kamau and Yusuf Migwa

Summary

Cassava is mainly grown in marginal soils and yields in farmers’ fields are low, about 6-8 t ha–1 with possible attainable yields of 35-45 t ha–1. Research on cassava intercropping and soil fertility requirements is relatively more recent than other aspects of cassava production, and available information is scanty and in some cases contradictory. There is, therefore, a need to evaluate the performance of improved, high-yielding, disease and pest resistant varieties with improved nutrition when intercropped with legumes under different environments. The objective of the project is to evaluate the yield response of some improved cassava varieties to fertiliser when intercropped with legumes.