Soil microbial biomass and activities as influenced by green manure legumes and N fertilizer in rice-wheat system

The objectives of this study were to assess the influence of green manure legumes and N fertilizer on soil microbial biomass and activities in rice (Oryza sativa) -wheat (Triticum aestivum) system. Soil samples (0-15 cm) were collected from field experiment established in 2001 involving mungbean (Vigna radiata), cowpea (Vigna unguiculata), soybean (Glycine max), sesbania (Sesbania rostrata), pigeonpea (Cajanus cajan) and guar (Cyamopsis tetragonoloba) as green manure in rice-wheat system in Peshawar valley, Pakistan. The results showed that the green manure legumes and N fertilizer application significantly increased the microbial biomass and activities in rice-wheat system. The average improvement gained from the green manure legumes relative to (fallow-based-rice-wheat) FRW, was 1.79 times for microbial activities, 1.70 times for microbial biomass-C (MBC), 1.49 times for microbial biomass-N (MBN), 1.82 times for C mineralization, 1.92 times for N mineralization, 3.36 times for bacterial population and 1.46 times for fungal population. The average improvement gained from N fertilizer (+N) relative to no N unfertilizer (0N), was 1.40 times for microbial activities, 1.17 times for MBC, 1.29 times for MBN, 1.42 times for C mineralization, 1.45 times for N mineralization, 1.17 times for bacterial population and 1.42 times for fungal population. Our results thus suggest that the microbiological attributes proved to be highly responsive and sensitive to the beneficial influence of green manure legumes in rice-wheat system and can be used as indicator of soil quality. (author)