Evaluating quality of composts made from organic agro-wastes and their influence on maize yield and soil fauna in Western Kenya
Degradation of soils' physical, chemical and biological properties in arable lands of sub-Saharan Africa mostly results from little or no organic resource application coupled with sub-optimal fertilizer application. A study was conducted in Buyangu and Ivakale villages, Kakamega over three seasons from March 2010 to August 2011 to evaluate the potential of six locally available organic biomasses namely; cow manure, maize stover, Tithonia diversifolia, sugarcane straw, bagasse and filtermud for compost production and their effect on soil quality, soil fauna diversity and on maize yields. Treatments consisted of six composts made from the six organic biomasses, inorganic fertilizer treatment and a no-input control and these were replicated four times in randomized complete block design (RCBD). Soil samples were analyzed for chemical and biological properties. Earthworms were collected using soil monoliths while nematodes were sampled and extracted using steel core samplers and Baerman pan technique, respectively. Data obtained were subjected to analysis of variance using GENSTAT statistical software while treatment differences were evaluated using least significant difference (LSD) at 5 % level of significance. Strength and statistical significance of soil chemical properties with macrofauna abundance and taxonomic richness was conducted using the programme CANOCO 3.1. There was no significant difference in chemical properties of the different composts types. Amending soils with composts significantly (P < 0.001) increased soils' N, C and P compared to no-input control plots. In these, C, Nand P increased by 90, 21 .and 2%, respectively upon addition of composts. The no-input control plots recorded a 37% increase in C, but a decline of 15% and 40% in Nand P, respectively. Fertilizer treated soils recorded an increases of 92, 26 and 81 % in C, Nand P, respectively. Earthworm abundance and biomasses were significantly (P < 0.001) higher in compost amended soils (38 individuals m-2 and 1.2 g m') compared to fertilizer and no-input control plots which had on average-l0 individuals m-2 and a biomass of 0.3 g m'. The positive relationships between macrofauna abundance and soil chemical properties were highly significant (P = 0.007). Generally, plant-parasitic nematodes decreased with addition of composts, while bacteria-feeding nematodes increased with application of composts. Similar to macrofauna, the positive relationships between soil chemical properties and nematode density were also highly significant (P = 0.001). Maize yields over the three seasons were significantly (P < 0.001) highest in fertilizer treated plots (4.4 t ha'), followed by composts (2.8 t ha') and lowest in no-input controls (1.4 t ha'), However, the benefit cost ratio obtained from yields was highest on composts treated plots followed by fertilizer treated plots and lowest in control plots. The results of'this study demonstrate the potential of composts in improving soil fertility and hence productivity.