Influence of manures and inorganic fertilizers on soil organic carbon and enzyme activities in rice under flooded conditions

In a laboratory and field study, long-term application of organic manures and inorganic fertilizers in an tropical inceptisol under rice-rice cropping system at Andhra Pradesh Rice Research Institute, Maruteru, Andhra Pradesh resulted in different fractions of carbon and soil enzyme activities. Microbial biomass carbon (MBC), readily mineralizable Carbon (RMC), acid hydrolysable Carbon (AHC), water soluble carbon (WSC), permanganate oxidizable carbon (POC) were found to be higher in FYM and inorganic NPK treatments. In the field study, acid phosphatase, alkaline phosphatase, dehydrogenase and β-D-glucosidase activity of inorganic NPK + FYM recorded significantly higher activity of followed by FYM, inorganic NPK, inorganic N and control. All the enzymes recorded significantly increased activity upto panicle stage of crop growth and thereafter decreased. A two fold higher activity of acid phosphatase, four-fold of alkaline phosphates and dehydrogenase and seven fold of β-D-glucosidase was recorded at panicle initiation stage of crop growth. The enzyme activities were significantly correlated with MBC and TOC contents of soils and interrelationship between the different enzymes activities also existed in the cropped soil under flooded conditions.