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-degrad ed soil. Principal component analysis demonstrated that soil organic m atter related nutrient dynamics was the major contributor to explain t he total variance (>80%) of the sites under the prevailing experimenta l conditions. Highest loadings with the major principal component were provided by microbial biomass, alkaline phosphatase, total N, beta-gl ucosidase and organic C. Contrasting fallow management systems (alley cropping, live mulch, planted fallow, controls in long-term experiment s) at three sites differing in degree of soil degradation could be eva luated adequately by these indicators. beta-Glucosidase indicated soil quality changes better than total organic carbon. Alkaline phosphatas e was more sensitive than microbial biomass in characterizing the effe cts of improved fallow management on site degradation. Acid phosphatas e and protease were not considered sensitive indicators for soil quali ty evaluations of these long-term management trials. Pueraria sustaine d soil quality on the non-degraded site but did not improve the severe ly degraded site, suggesting that pueraria is a soil fertility mainten ance crop. In contrast, senna improved the degraded sites and more so on the most severely degraded site. Apparently, senna can be considere d a suitable candidate for soil restoration purposes.