Soil Microbial and Biochemical Changes associated with Cropping Systems and Soil Depth in the Southern Guinea Savanna Zone of Nigeria

Abstract

Management practices under various cropping system have a significant influence on the population size and activity of microbial organisms in the soil. Little is, however, known of the impact of such effect in soil of the Nigerian savanna. A study was conducted to examine changes in soil microbial population, microbial biomass and phosphatase activity in four cropping systems (fallow, cassava, cassava/cowpea and rice) and at three soil depths (0-15cm, 15-30cm and 30-45cm) at a site in the southern guinea savannah zone of Nigeria. Soil moisture content and pH. Increased with depth, while soil organic carbon (SOC), total N and exchangeable base content decreased with depth. There was also a demonstrable effect of cropping system on soil properties, with fallow showing relatively higher pH and greater soil moisture, organic carbon and total N contents than the cultivated treatments. Among the cultivated system, rice had the most favorable effect on soil properties. Soil microbial populations, microbial biomass C (SMBC) biomass C:N ratio, as well as acid and alkaline phosphatase activities were responsive to cropping system, and were largely greater in the fallow and rice fields than in the other two systems. The soil microbial community and microbial biomass were largely dominated by fungal flora and this was probably as a result of relatively poor quality (high lignin and /or C:N ratio) of the organic matter input. Changes in microbial biomass N (SMBN) and phosphodiesterase activity, either due to cropping system or soil depth, were not significant indicating that these parameters are less useful as indicators of soil quality.