MICROBIAL BIOMASS ASSOCIATED WITH WATER-STABLE AGGREGATES IN FOREST, SAVANNA AND CROPLAND SOILS OF A SEASONALLY DRY TROPICAL REGION, INDIA

The distribution of microbial biomass associated with water-stable mac ro- and microaggregates in soils was studied along a forest-savanna-cr opland gradient. In both macro- and microaggregates, mean microbial bi omass C, N and P were maximum in forest and minimum in cropland soils. At all the sites microbial C was greater in the macroaggregate than t he microaggregate size class, whereas microbial biomass N and P were g reater in the microaggregates. The microbial C-to-nutrient ratios were lower for the microaggregates compared to macroaggregates. It is poss ible that these two size classes support two different types or compon ents (fungi-dominated and bacteria-dominated) of the food web in soil. There was a decrease in the amount of microbial C, N and P in both ma cro- and microaggregates along the forest-savanna-cropland gradient, w hich was due to the reduction of total soil organic matter. Total soil organic C and total N showed significant positive relations with both macro- and microaggregate microbial C and N, indicating that the latt er are limited by the quantity of soil organic matter.