Identification of organic materials, which can enrich the soil organic matter pool and improve the productivity of marginal lands, is a necessity in tropical countries. A study was conducted to comprehend the effect of organic materials of different quality on the soil carbon (C) pool size and N, P, K release from soil. Organic amendments (OA) with different complexities namely, cattle manure (CM), cattle manure-rice straw (CR), cattle manure-wood shavings (CW), and cattle manure-rice straw-wood shavings (CRW) mixtures as fresh (f) or incubated for two months (i), were used in a leaching column study, soil incubation experiment and greenhouse experiment using maize (Zea mays L.) as the test plant. The N, P and K release pattern from soil, soil organic matter content and biomass of maize in OA added soils compared to fertilizer-only (SF) and soil-only (S) treatments were determined. The nitrogen release and microbial activity were higher in fresh-OA added soils compared to other treatments. Phosphorous and K were higher in soils amended with incubated-OA than fresh-OA. The highest N, P and K release was obtained with CM-i, CRWi and CM-f, respectively. Shoot biomass of maize was enhanced by 20-40% with the application of incubated-OA compared to SF. The total soil organic C and active organic C ranged from 10.85 to 13.50 g/kg and 0.31 to 0.64 g/kg, respectively, with soils treated with OA showing significantly high values compared to the control. The organic amendments used as fresh or incubated materials, did not impede plant growth and generally maintained or improved the soil nutrient status and C pool. Incubating OA prior to application improved the nutrient availability in soil.
Tropical Agricultural Research Vol. 25 (2): 201 – 213 (2014)