An incubation study was carried out to investigate the influence of nitrogen rates to determine optimum C/N ratio under various moisture levels for straw decomposition and sequester carbon (C) in the soil. The aim was to observe straw carbon mineralization through measuring the amount of CO 2 evolution. A clay loam topsoil mixed with maize straw was supplied with four nitrogen rates (0.04, 0.08, 0.16, 0.32 g N/kg) using (NH 4 ) 2 SO 4 to adjust C/N ratios at 82, 42, 20, and 10. Soil moisture was maintained at 55%, 70%, 85%, and 100% of field capacity incubated at 25°C for 53 days. The experiment was set up with 16 treatments arranged in complete randomized design. Results showed that mixing of straw with soil increased 50% cumulative CO 2 -C compared to controls. Averagely, about 44% of added maize straw C was mineralized to CO 2 -C. Straw addition along with nitrogen and moisture had significant relationships (P < 0.05) to cumulative CO 2 -C, soil organic C and microbial biomass C. There was a highly significant relationship (R 2 = 0.99) between CO 2 -C emission and incubation time.

A laboratory study was conducted to investigate efficacy of locally produced microbial inoculants with different concentrations on microbial respiration from soils with and without addition of wheat straw incubated at 20 and 25°C temperatures for 73 days. The results indicated that the soil microbial community structure and activities were obviously influenced by microbial inoculants. In general, whereas all inoculants levels were successfully established to different extents on the straw, none significantly improved decomposition in either soils or straw amended treatments. Additions of microbial inoculants expedite the decomposition and CO 2 evolution process. CO 2 -C emission was regularly determined and results revealed microbial inoculants had little (10%) while straw addition significantly increased decomposition rates and cumulative CO 2 -C by 39% in straw amended than controls. Straw addition into soil had significant relationships (p < 0.05) with cumulative amounts of C; soil organic C, microbial biomass nitrogen. There was highly significant relationship between CO 2 -C emission and incubation period (R 2 =0.94). In conclusion, microbial inoculants and straw incorporation will enhance CO 2 -C evolution, soil carbon and microbial biomass, thus improving soil quality.