EFFECTS OF FARMYARD MANURE AND INORGANIC FERTILIZER ON THE DYNAMICS OF SOIL MICROBIAL BIOMASS IN A TROPICAL DRYLAND AGROECOSYSTEM

Changes in the soil microbial biomass following applications of farmya rd manure and inorganic fertilizer, alone and in combination, were stu died for two annual cycles in a rice-lentil crop sequence grown under rainfed tropical dryland conditions. During the two annual cycles the microbial biomass C range (mu g g(-1)) was 146-241 (x=204), 191-301 (2 45), 244-382 (305), and 294-440 (365) in control, fertilizer, manure a nd manure+fertilizer plots, respectively. The corresponding ranges for microbial biomass N (mu g g(-1)) were 16.5-21.0 (19.5), 20.4-38.2 (26 .0), 23.0-34.6 (27.0) and 26.2-42.4 (33.3), and for microbial biomass P (mu g g(-1)) 4.4-8.2 (7.0) 6.0-11.2 (9.6), 11.2-22.0 (17.0), and 10. 0-25.4 (18.3). The maximum increase in the microbial biomass, due to t hese inputs was observed under the manure+fertilizer treatment followe d, in decreasing order, by manure alone and fertilizer alone. Within i ndividual crop periods the levels of microbial biomass decreased sharp ly from the seedling to the flowering stage and then increased slightl y with crop maturity. The maximum levels of microbial biomass C and P were observed during the summer fallow The maximum accumulation of mic robial biomass N occurred in the early rainy season, immediately after the soil amendments. Microbial biomass C, N, and P were positively re lated to each other throughout the annual cycle.