Effect of integrated nitrogen and phosphorus management on soil enzymatic activities

Soil enzymatic activities respond sensitively to nutrient management practices and provide valuable insights into soil microbial functioning and nutrient cycling. Dehydrogenase and urease enzymes are widely used indicators of overall microbial activity and nitrogen transformation in soils. A field experiment was conducted during two consecutive years (2022-23 and 2023-24) to evaluate the effect of nitrogen and phosphorus management practices on soil dehydrogenase and urease activities at different crop growth stages. The experiment consisted of six nitrogen management options involving integrated use of inorganic fertilizers, organic amendments, and bio-inputs, and four phosphorus management options involving basal and split applications, arranged in a factorial randomized block design. Soil samples were collected at 30 and 60 days after transplanting (DAT) and at harvest, and enzyme activities were determined using standard analytical procedures. Pooled analysis of data indicated that both dehydrogenase and urease activities increased significantly from 30 DAT to 60 DAT and declined at harvest. Integrated nitrogen management treatments recorded significantly higher enzymatic activities compared to conventional fertilizer practices at all stages. Among phosphorus treatments, application of 100 per cent recommended dose as basal application resulted in the highest enzyme activity. Interaction effects between nitrogen and phosphorus treatments were non-significant, indicating independent contributions of these nutrients to soil biological activity. Enhanced enzymatic activity under integrated nutrient management was attributed to improved substrate availability, increased microbial proliferation, and favorable soil conditions. The results emphasize the importance of balanced and integrated nitrogen and phosphorus management for improving soil biological health and sustaining nutrient cycling in intensive cropping systems.