Impact of Rock Phosphate based-PROM (Phosphorus Rich Organic Manure) on Enzyme Activities and Nutrient Availability in Calcareous Soil under Soybean Cultivation

A field experiment was conducted at Research Farm, College of Agriculture, Pune during kharif 2023. The object of this experiment was to study comparative efficiency of phosphorus application through phosphorus rich organic manure (PROM), single super phosphate and diammonium phosphate (DAP) for soybean on enzyme activities and nutrient availability in highly calcareous soil. This experiment consisted of two organic sources (PROM and vermicompost) and two inorganic sources of phosphorus (SSP and DAP) along with their levels @ 50, 75 and 100 % imposed for soybean in highly calcareous soil. The treatments comprised T1 - absolute control, T2 - RDF (50:75:45 kg ha-1 N: P2O5: K2O), T3 - 50% P2O5 through PROM, T4 - 75% P2O5 through PROM, T5 - 100% P2O5 through PROM, T6 - 100% P2O5 through DAP + FYM @12.5 t ha-1, T7 - 100% P2O5 through SSP + FYM @12.5 t ha-1 and T8 - 100% P2O5 through vermicompost replicated thrice in randomized block design imposed to soybean in highly calcareous soil.

Results on post harvest fertility status of highly calcareous soils were concluded that incorporation of PROM and vermicompost for the replacement of 100 % P2O5 found superior for build up available nitrogen, phosphorus and potassium. Further, incorporation of 100 % P2O5 through PROM reported 75.48%, 122.07 %, 169.95 % and 104.09 % increase in DTPA extractable Fe, Mn, Zn and Cu over absolute control respectively. The data on enzyme activities in highly calcareous soil revealed that incorporation of P2O5 either through organic and inorganic sources recorded higher urease (30.93 and 29.22 µg NH4+-N g-1 soil hr-1), acid (6.07 and 6.74 µg PNP g-1 soil hr-1) and alkaline phosphatase (11.34 and 10.34 µg PNP g-1 soil hr-1) and dehydrogenase (14.30 and 10.40 µg TPF g-1 soil 24 hr-1) activity at 50 % flowering of soybean than that assayed at harvest of soybean. It is inferred that incorporation of PROM or vermicompost for the substitution of either 75 or 100 % P2O5 reported significantly higher activities of enzymes in calcareous soil than that of inorganic fertilizers (SSP and DAP) or recommended dose of fertilizer or absolute control.