Variation in Soil C and P Fractions Associated with Microbial Biomass

The variations in soil carbon (C), phosphorus (P) fractions, microbial indices, and their mechanisms to drive P mobilization are still poorly understood in calcareous soils. An incubation study was set up to evaluate the changes in microbial biomass index (C and P), soil organic C, and Pi fractions. The incubation study with a two-factor completely randomized design including manure source, poultry manure (PM), cow manure (CM), goat manure (GM), and mixed manure (MM), no manure (CK), and inorganic P (Pi) rates (P 0 = 0, P 50 = 50, and P 100 = 100 mg kg −1 P 2 O 5 ) was conducted in the greenhouse. Combined application of PM and Pi (100 mg kg −1 ) significantly improved the soil physicochemical traits, i.e., total P (692.88 mg kg −1 ), Olsen P (32.39 mg kg −1 ), soil organic carbon (4.21 g kg −1 ), and particulate organic carbon (2.58 g kg −1 ). The same treatment significantly ( p ≤ 0.05) increased microbial biomass carbon (MBC) and microbial biomass phosphorus (MBP) by 173.89 and 42.03 mg kg −1 , respectively. The moderately labile Ca 8 -P pool was greater than the Ca 2 -P pool under PM with Pi at 100 mg kg −1 , whereas the Ca 8 -P pool was improved by 49 mg kg −1 compared to CK. Moreover, the Ca 8 -P pool had a significant ( p ≤ 0.05) relationship with MBC and MBP. Based on the results, it is concluded that the application of PM along with Pi 100 mg kg −1 builds up microbial biomass, which can immediately store a higher amount of readily soluble P and protect it from fixation, eventually improving soil P availability.