Soil Microbial Biomass and Water-Soluble Organic Carbon in Crop Rotation Systems in a Moist Tropical Savanna Alfisol

Abstract

Knowledge of the dynamics of microbial biomass and water-soluble organic carbon (WSOC) are important in understanding microbial cycling of nutrients, especially where external inputs of nutrients are low. We investigated the effect of preceding legumes-soybean (Glycine max), cowpea (Vigna unguiculata L.), Centrosema pascuorum, and a natural fallow on soil microbial biomass carbon (SMBC) and nitrogen (SMBN) and WSOC and their relationship with soil pH, soil organic carbon (SOC) and total N in the second season of maize cropping. The SMBC and its proportion in SOC and WSOC were significantly (P<0.05) higher under legume rotations than fallow rotation. Biomass C/N ratios of the soils
under soybean, cowpea, Centrosema and fallow rotations were 7.1, 8.3, 5.7, and 4.9, respectively, suggesting bacteria dominance in Centrosema and fallow, and fungi dominance in soybean and cowpea rotations. Soil microbial biomass and WSOC were significantly (P<0.01) correlated with soil pH and total N while SMBC and WSOC were significantly (P<0.01) correlated with SOC. These results suggest that the soil pH and total N are mitigating factors that affect the growth and activity of soil micro flora in these soils.

Keywords: Alfisol, crop rotation, microbial biomass, savanna, water-soluble organic carbon.

Nigerian Journal of Soil and Environmental Research Vol. 7 2007: pp. 45-52