Potentiality of diverse organic inputs with low chemical fertilizer on microbial biomass carbon, soil enzymes and crop yield in paddy soil

Field trials were conducted on rice during 2008–09 and 2009–10 to realize the potentiality of diverse organic inputs on soil biological properties and crop yield under reduced chemical fertilizer. Application of diverse organic inputs significantly improved the microbial biomass carbon (MBC), organic carbon (OC), dehydrogenase (DH) activity and fluorescein di-acetate (FDA) hydrolase in paddy soil. Among the organic inputs, dual culture of Azolla caroliniana with 50% of recommended N P and K fertilizer exhibited clear increase in MBC (220.46 μg./g.), OC (11.43g./kg.), DH (294.98μg.TPF/g./24hrs.) activity and FDA (10.52μg. fluorescein/g./hrs.) hydrolase. Conversely, the rock phosphate carrying enriched compost stimulated the higher level of (366.12 μg. p-nitrophenol/g./hrs.) phosphomonoesterase(PMEase) activity. MBC showed significant correlation with soil OC (r=0.883**), DH (r=0.922**) activity and FDA (r=0.675**) hydrolase except PMEase activity. Similarly, OC also displayed strong correlation with DH (r=0.836**) activity and FDA (r=0.842**) hydrolase but poorly with PMEase (0.269*) activity. Of the six organic inputs, dual culture of A. caroliniana demonstrated maximum rice yield (4.18t./ha.) followed by insitu application of Sesbania rostrata (4.08t./ha.) under reduced chemical fertilizers and the yields were comparable with recommended chemical fertilizer (3.91t./ha.).