Short term effects of different green manure amendments on the composition of main microbial groups and microbial activity of a submerged rice cropping system

Abstract

Green manuring is a feasible agricultural practice to mitigate soil degradation and loss of biodiversity caused by long term application of inorganic fertilizer. However, the effect of the types of green manure (legume vs nonlegume) on soil microbial groups and activities are largely not known. Field experiments were conducted to investigate the effects of incorporating two green manures that originated from residues of barley (Hordeum vulgare) and hairy vetch (Vicia villosa), on microbial groups, biomass, enzyme activities, nutrient availability of soil, and crop yield in a mono-rice cropping system. Green manure biomasses were applied on an equal nitrogen biomass basis. We found that, compared to inorganic fertilizer, green manures amendment significantly increased composition of main microbial groups, microbial biomass C (MBC) and hydrolase activities of soil. Total PLFAs, Gm + bacteria, fungi and actinomycetes PLFAs were markedly increased by the barley residue amendment whereas Gm- bacteria PLFA was mostly increased by the hairy vetch residue amendment. The higher hydrolase activities involved in C cycling were observed in the barley treatments, whereas soil enzyme activities involved in N and P cycling were higher in the hairy vetch treatments. Probably, differences between the two treatments dependent on different chemical composition of the green manures incorporated into the soil and their mineralization controlled by the soil C:N ratio. A decrease in oxidative enzyme activities and higher fungi: bacteria ratio as a result of the green manure amendment, in particular barley, suggested the potential of barley biomass incorporation to enhance C storage in submerged rice cropping systems.