Effect of different sources of organic manures on phosphorus release rate, microbial population and enzyme activities in vertisol

Abstract

An incubation study entitled “Enzymatic Activities and Phosphorus Availability as Influenced by Different Organic Manures in Vertisol” was conducted during 2024–2025 at the Division of Soil Science, College of Agriculture, Kolhapur. The experiment was laid out in a CRD with six treatments and four replications. The treatments included: Absolute Control, GRDF (50:75:45 N:P₂O₅:K₂O kg ha-¹ + FYM 10 t ha-¹), RD NK + 100% RD-P₂O₅ + PMC 2.0 t ha-¹, RD NK + 75% RD-P₂O₅ + PMC 4.0 t ha-¹, RD NK + 100% RD-P₂O₅ + PROM 0.5 t ha-¹, and RD NK + 75% RD-P₂O₅ + PROM 1.0 t ha-¹. The study was conducted for 90 days using the discard method under laboratory conditions. The phosphorus release rate peaked between 30 and 45 days of incubation, with the highest release (5.23 mg kg-¹) observed under RD NK + 75% RD-P₂O₅ + PROM 1.0 t ha-¹. In the later phase (75–90 days), GRDF treatment showed the highest phosphorus release rate (1.78 mg kg-¹). In respect of enzymatic activity the higher alkaline (67.65 µg PNP g-¹ soil hr-¹) and acid phosphatase (20.91 µg PNP g-¹ soil hr-¹) activities were recorded at 45 days under RD NK + 75% RD-P₂O₅ + PROM 1.0 t ha-¹. However, the GRDF treatment recorded the highest alkaline phosphatase activity (59.59 µg PNP g-¹ soil hr-¹) at 90 days. Microbial populations also responded positively to organic amendments. At 45 days, RD NK + 75% RD-P₂O₅ + PROM 1.0 t ha-¹ recorded significantly higher bacterial (25.83 ×10⁶ cfu g-¹ soil) and PSB populations (13.32 ×10⁵ cfu g-¹ soil).