Organic residue effects on soil physical and chemical properties in Kenya

This study was designed to evaluate the influence of organic resource management on selected soil chemical properties in central and western highlands of Kenya. Three ongoing experiments (Kabete, Maseno and Embu) involving the integration of organic and inorganic resources. as nutrient sources were selected. The choice of these experiments was based on the different organic resources applied, their lifespan as well as their unique ecological locations that characterize most smallholder fanning areas in Kenya. These experiments involved the application of Tithonia diversifolia, Senna spectabilis, Leucaena leucocephala and Calliandra calothyrsus as organic nutrient sources to a maize crop which were compared to fertilizer and control treatments. Soils were sampled from (SOM) plays an important role in maintaining these experiments and analysed for soil structure, water-holding capacity, the morganicnitrogen, total carbon, nitrogen, bulk microbial biomass and soil fauna, and in density and potassium permanganate nutrient cycling. The de~line ofSOM with oxidizable carbon. In addition, SOM cropping is a major factor affecting aggregate and size fractionation was used sustainability of cropping systems to determine the quantity of the various (Buyanovzky et aI., 1994). Nutrient have SOM fractions formed. Soil C, Nand BC gradually been depleted by crop harvest and KMnO 4-C values in the three removals, leaching and soil erosion to the experiments varied among sites depending extent to which soil fertility replenishment on the amounts of the organic residues has been recommended as a necessary applied as well as the duration for application investment in natural resource capital (Izac, indicating that organic residue management 1997). Studies indicate that soil physical, practices indicating that organics have a chemical and biological properties can profound impact on the final SOM pools. sustainably be improved through the Kabete experiment had thenarrowestC, N improvement of SOM (Paul, 1984). and DC values pointing to the young age of Practices such as alley cropping and this experiment as well as the low quantity biomass transfer offer the potential of doing of the organic residues applied. hand, Einbu experiment had soil C values above the critical level of 2.0% indicating the effect of continued application of organic residues. Using the BC labelling technique revealed greater shifts in C signatures to a C3 carbon type between the organic and the control treatments in Embu and Maseno experiments which indicated greater labelling effect from the organic residues applied.