Organic manuring in rice-based cropping system: Effects on soil microbial biomass and selected enzyme activities

Abstract

Soils exclusively amended with poultry manure, farmyard manure, sesbania and gliricidia for three successive rice-rice-cowpea cropping systems were incubated as such or after fresh addition of the respective organic manure at 37 ± 1°C under submergence. The treatments also included fresh incorporation of these organic manures into soils with no amendment history. Soil microbial biomass (total, fungi, actinomycetes, bacteria), biomass C, N flush and the activities of enzymes like amylase, cellulase, arylsulfatase, ᵦ-glucosidase and inorganic pyrophosphatase were determined at different stages of incubation and the data pertaining to peak enzyme activity (30th day) are reported. Soils amended with organic manures consistently registered significantly greater microbial biomass, biomass C, N flush and enzyme activities compared to the unamended soil. All the enzymes were significantly activated to different degrees, which however, varied with the type of organic manure added to soils. Positive relationships between relevant soil properties and enzyme activities suggest that addition of organic manures increased microbial activity/ diversity and C turnover, which subsequently led to greater enzyme synthesis and accumulation in the soil matrix. It is, therefore, apparent that soil microbial biomass and enzyme activities are sensitive even to short-term organic manuring.