Effect of Integrated Nitrogen Management and Spacing on Soil Fertility Status and Soil Microbial Properties in Kalmegh (Andrographis paniculata)

The adoption of integrated nitrogen management (INM); which entails the combined application of organic and inorganic nitrogen sources; has been widely recognised for its role in improving nutrient availability; enhancing soil fertility; and promoting sustainable agricultural production systems. A field experiment was conducted to investigate the influence of integrated nitrogen management and plant geometry on soil fertility parameters and soil microbial properties in Kalmegh (Andrographis paniculata Nees.); a medicinally important crop. The experiment was laid out in a factorial randomised block design (FRBD); comprising four nitrogen source treatments with varying proportions of vermicompost and inorganic fertilisers; in combination with three plant spacing levels; thereby enabling a comprehensive assessment of their interactive effects on soil health indicators. Soil samples collected after harvest were analyzed for available nitrogen (N); phosphorus (P₂O₅); potassium (K₂O); and populations of major soil microorganisms such as actinomycetes; bacteria; and fungi. The results indicated that integrated nitrogen management had a significant influence on soil fertility status and microbial activity. Application of 100 per cent nitrogen through vermicompost resulted in significantly higher available soil nutrients; recording 189.90 kg ha⁻¹ of nitrogen; 24.91 kg ha⁻¹ of phosphorus; and 375.76 kg ha⁻¹ of potassium; compared to treatments receiving nitrogen solely through inorganic fertilizers. Vermicompost-based treatments also markedly improved soil biological properties by enhancing microbial populations; with the highest counts of actinomycetes (3.92 × 10⁴ cfu g⁻¹); bacteria (28.49 × 10⁶ cfu g⁻¹); and fungi (4.39 × 10⁵ cfu g⁻¹). This improvement may be attributed to increased organic matter content; better nutrient availability; and favorable soil conditions that support microbial proliferation. Plant spacing significantly influenced soil nutrient availability and bacterial population. Wider spacing (30 × 15 cm) resulted in higher available nitrogen; while spacing of 20 × 20 cm recorded higher phosphorus availability. The closest spacing (30 × 10 cm) registered maximum potassium availability and bacterial population. However; plant spacing did not significantly affect actinomycetes and fungal populations. Interaction effects between nitrogen sources and plant geometry were found to be non-significant for soil fertility and microbial parameters. The study concludes that integrated nitrogen management; particularly the application of vermicompost; combined with appropriate plant spacing; plays a crucial role in improving soil fertility status and enhancing soil microbial activity in Kalmegh cultivation; thereby contributing to sustainable soil health and long-term productivity.