Long-term impact of grain legumes and nutrient management practices on soil microbial activity and biochemical properties

Sustainability of rice-wheat rotation is questioned with soil degradation and depleting natural resources. The study aimed to assess the long-term impact of four crop rotations [rice-wheat, rice-wheat-mungbean, rice-chickpea, rice-wheat-rice-chickpea (2-year rotation)], each consisted of three nutrient treatments [control, integrated nutrient management (INM), and chemical fertilizers (RDF)] on soil carbon pools, soil microbial, and biochemical properties. Mungbean inclusion in rice-wheat rotation increased soil organic carbon (SOC) and microbial biomass carbon (MBC) by 17% and 27%. Rice-wheat-mungbean rotation increased soil enzymes activities over rice-wheat rotation, prominent on arylsulfatase (41%), dehydrogenase (38%), and phosphatases (32%). Rice-chickpea rotation had higher alkaline phosphatase (10%), beta-glucosidase (13%), and protease (6%) activities over rice-wheat rotation. Rice-wheat-mungbean rotation increased the MBC/SOC and reduced MBC/MBN ratio over rice-wheat rotation, which indicates increased lability of soil carbon and enhanced nitrogen cycling rate. The INM treatment increased SOC (20%), MBC (53%), soil respiration (9%), and enzymes activities over RDF treatment, which was primarily attributed to higher organic matter input through farmyard manure and residues recycling. The higher SOC and microbial activity in legume-inclusive rotations influenced the base-crop (rice) productivity. Thus, the inclusion of grain legume and INM could improve microbial activity and biochemical functions in tropical rice soils.