Soil microbiological parameters as indicators of soil quality under improved fallow management systems in south-western Nigeria

Soil microbiological and soil biochemical parameters (pH, exchangeable basic cations, inorganic and organic phosphorus pools, total organic carbon and total nitrogen, microbial biomass carbon, acid and alkaline phosphatase, beta-glucosidase and protease activity) were identified as indicators of soil quality under improved fallow management systems with senna, leucaena and pueraria on severely degraded and non-degraded soil. Principal component analysis demonstrated that soil organic matter related nutrient dynamics was the major contributor to explain the total variance (>80%) of the sites under the prevailing experimental conditions. Highest loadings with the major principal component were provided by microbial biomass, alkaline phosphatase, total N, beta-glucosidase and organic C. Contrasting fallow management systems (alley cropping, live mulch, planted fallow, controls in long-term experiments) at three sites differing in degree of soil degradation could be evaluated adequately by these indicators. beta-Glucosidase indicated soil quality changes better than total organic carbon. Alkaline phosphatase was more sensitive than microbial biomass in characterizing the effects of improved fallow management on site degradation. Acid phosphatase and protease were not considered sensitive indicators for soil quality evaluations of these long-term management trials. Pueraria sustained soil quality on the non-degraded site but did not improve the severely degraded site, suggesting that pueraria is a soil fertility maintenance crop. In contrast, senna improved the degraded sites and more so on the most severely degraded site. Apparently, senna can be considered a suitable candidate for soil restoration purposes.