Effect of combined application of organic and inorganic phosphatic fertilizers on dynamic of microbial biomass in semi-arid soil

A silt loam soil was amended with finely ground biogenic waste compost (BWC with C/N 12), farmyard manure (FYM with C/N 19) and sugar cane filter cake (SFC with C/N 14) mixes with inorganic phosphorus fertilizer and also applied in the form of enriched inorganic phosphorus fertilizer. Each organic amendment was applied at the rate of 0.5 mg C g(-1) soil, and incubation was carried out at 25 degrees C and 50% water holding capacity for a period of 90 days. Soil samples were collected on days 0, 30, 60 and 90 of incubation and analyzed for microbial indices (microbial biomass C and microbial biomass P) by fumigation extraction technique and biochemical (phosphatase and dehydrogenase activity) parameters. The significant increase was recorded in cumulative respiration and microbial indices after application of amendments compared to unamended soil (control) due to the availability of easily decomposable organic carbon and P by organic amendments. Application of all amendments increased MBC, MBP and available P by 13%, 28% and 14% respectively with greater effect with inorganic P-enriched SFC and FYM followed by BWC. Microbial indices and enzyme activity showed the same temporal pattern with maximum increase on day 0 and 30. CO2-C 24 h(-1) emission was also higher in the soils amended with organic sources compared to the unamended soil. It is concluded that use of organic amendments enhanced phosphorus bioavailability by increasing microbial activity and enzymatic activity.