Influence population behaviour of soybean-rhizobia on nitrogen fraction under different cropping system in Vertisols of central India

To assess the indigenous composition (slow and fast growers) of soybean-rhizobia in Vertisols under different cropping system and their impact on nitrogen (N) fraction in soil. The soils were from soybean-based (soybean-wheat and soybean-chickpea) or cereal-based (maize-wheat, rice-wheat and maize-chickpea) rotations during 2013-15. Sampling site for soybean-wheat system were three selective treatments-absolute control, recommended dose of fertilizers (RDF) and RDF+FYM were considered. Ratio of fast-growing soybean-rhizobia was more in those cropping system where soybean was one of the crops while population of slow-growers were more with cereal-cereal or maize-chickpea cropping system. With regard to nodulation and N symbiotic efficiency; better performance (number of nodules, dried weight, N-content and Ntot-uptake) was found by slow-growing as compared to fast growing rhizobia. Irrespective of cropping system, maximum SOC was found at maximum vegetative growth in soybean-wheat rotation (5.7 g kg-1 soil) with application of RDF+FYM, while minimum (3.2 g kg-1 soil) with in control of soybean-wheat. Available and soil-Ntot was found more in kharif season where soybean was included in the cropping system as compared to other system. Soil aeration and legume-based more supported conversion of NH4+-N to NO3--N during the rabi season as compared to kharif and cereal-based respectively. These results imply that inclusion of any leguminous crop in cropping system improved the N-stock in soil.