Effect of organic and inorganic sources of nutrients on soil microbial activity and soil organic carbon build-up under rice in west coast of India

The effect of medium-term (5 years) application of organic and inorganic sources of nutrients (as mineral or inorganic fertilizers) on soil organic carbon (SOC), SOC stock, carbon (C) build-up rate, microbial and enzyme activities in flooded rice soils was tested in west coast of India. Compared to the application of vermicompost, glyricidia (Glyricidia maculate) (fresh) and eupatorium (Chromolaena adenophorum) (fresh) and dhaincha (Sesbania rostrata) (fresh), the application of farmyard manure (FYM) and combined application of paddy straw (dry) and water hyacinth (PsWh) (fresh) improved the SOC content significantly (p < 0.05). The lowest (p < 0.05) SOC content (0.81%) was observed in untreated control. The highest (p < 0.05) SOC stock (23.7 Mg C ha(-1)) was observed in FYM-treated plots followed by recommended dose of mineral fertilizer (RDF) (23.2 Mg C ha(-1)) and it was lowest (16.5 Mg C ha(-1)) in untreated control. Soil microbial biomass carbon (C-mb) (246 mu g g(-1) soil) and C-mb/SOC (1.92%) were highest (p < 0.05) in FYM-treated plot. The highest (p < 0.05) value of metabolic quotient (qCO(2)) was recorded under RDF (19.7 mu g CO2-C g(-1) C-mb h(-1)) and untreated control (19.6 mu g CO2-C g(-1) C-mb h(-1)). Application of organic and inorganic sources of nutrients impacted soil enzyme activities significantly (p < 0.05) with FYM causing highest dehydrogenase (20.5 mu g TPF g(-1) day(-1)), phosphatase (659 mu g PNP g(-1) h(-1)) and urease (0.29 mu g urea g(-1) h(-1)) activities. Application of organic source of nutrients especially FYM improved the microbial and enzyme activities in flooded and transplanted rice soils. Although the grain yield was higher with the application of RDF, but the use of FYM as an organic agricultural practice is more useful when efforts are intended to conserve more SOC and improved microbial activity.