F.O. Ayuke

Evaluating effect of mixtures of organic resources on nutrient release patterns and uptake by maize

To supplement high costs of inorganic fertilizers, smallholder farmers in the tropics are likely to increase the use of appropriate plant residues as an alternative source of plant nutrients especially nitrogen (N) and phosphorus (P). To maximize benefit accrued from these materials, synchronizing nutrient release patterns of the materials with crop’s nutrient requirements need to be understood. Consequently, this study was undertaken to: (1) evaluate the effect of plant residues on mineralization and N-release patterns, (2) evaluate the N release patterns of mixtures of low and high quality organic materials and synchrony with maize uptake. Incubation studies were established for 12 weeks using six selected plant residues: which included Leucaena leucocephala,Croton macrostachyus,Calliandra calothyrsus,Tithonia diversifolia,Sorghum bicolor and rice (Oryza sativa) husks.Soil samples were taken at 2 weeks interval for ammonium nitrogen (NH4 +-N) and nitrate nitrogen ( NO3 --N) determination.

Legume Based Cropping and Soil Biodiversity Dynamics

The soil is home to an enormous diversity of organisms, many of which are beneficial, while a small and equally diverse proportion contains harmful organisms. Legume cropping and husbandry practices impact negatively or positively on diversity. These changes in biodiversity may be quantitative and/or qualitative. Sustainable management of diversity in soils involves an ecosystem approach which encourages the establishment of equilibria between the organisms in the soil. It is evident that the diversity of beneficial organisms in the soil can be harnessed to improve and sustain crop productivity with minimal external inputs. Legumes will continue to play a central role in the supply of plant nutrients and in the establishment of a self-regulating ecosystem which is based on a diverse range of organisms.

Chapter 5:Agrobiodiversity and Potential Use for Enhancing Soil Health in Tropical Soils of Africa

a Department of Land Resource Management and Agricultural Technology, University of Nairobi, P.O Box 29053-00625, Nairobi, Kenya; b Department of Agricultural Economics, University of Nairobi, P.O Box 30197-00100, Nairobi, Kenya; c School of Biological Sciences, University of Nairobi, P.O Box 30197-00100, Nairobi, Kenya; d Department of Plant Sciences, University of Nairobi, P.O Box 30197-00100, Nairobi, Kenya; e World Agroforestry Centre, P.O Box 30677, Nairobi, Kenya*Corresponding author *E-mail: fredrick.ayuke@yahoo.com

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.