Soil microbial biomass (MB) is the main driving force in nutrients cycling, especially carbon (C), nitrogen (N) and phosphorus (P) which are often served as good soil productivity indicator in integrated management practices of agricultural ecosystems. This study was designed under greenhouse experiment to assess the effect of soil compaction, Bradyrhizobium inoculation and nitrogen fertilizer applicationon microbial biomass C and N and their proportion in soil C and total N. Soil microbial biomass carbon (MB-C) and microbial biomass nitrogen (MB-N) were determined by Fumigation Extraction method (FE). Compared to compacted soils, MB-C and MB-N were higher in un-compacted soils, with percent differences of 2.63 % for MB-N and 6.04 % for MB-C. Biomass as a percent of soil C and total N obtained under continuous sole maize was significantly lower than others Brandyrhizobium inoculated or un-inoculated soybean-maize cropping systems with difference of 19.32 and 36.36 % for rotation inoculated, 7.83 and 15.36 % for rotation un-inoculated, 22.19 and 20.06 % for intercrop inoculated and 14.62 and 12.54 % for intercrop un-inoculated respectively. The results obtained from various fertilizer treatments showed that biomass as a percent of soil C and total N increased significantly, as compared to control, which increased with additional increase in N. The application of 120 kg N ha-1 produced the highest biomass as a percent of soil carbon, followed by 80 kg N ha-1, while the least value was obtained under zero application of N. Microbial biomass carbon and nitrogen as a percent of soil total nitrogen was significantly higher at 80 kg N ha-1 which shows increasing trend with N fertilizer application rates and decreased at 120 kg N ha-1, suggesting better soil productivity improvement at 80 kg N ha-1 under cropping systems with bradyrhizobium inoculated soybean. The findings tent to advocate the need for inclusion of bradyrhizobium inoculation in legume-maize-based cropping systems to improve soil microbial biomass especially under less soil disturbances.
Keywords: Compaction, Brandyrhizobium Inoculation, Nitrogen Fertilizer, Microbial biomass, Greenhouse.