Crop management systems influence soil nitrogen fractions and biological activity in semi-arid agroecosystems

Nitrogen (N) availability is a major constraint to crop production in semi-arid rainfed regions. Crop management systems differ mainly in how nutrients are supplied and managed. Natural farming (NF) uses bioinoculants and mulching, organic farming (OF) is based on farmyard manure, integrated crop management (ICM) combines farmyard manure with urea, and conventional farming (CF) relies only on mineral fertilizers. Although interest in NF and OF is growing, information is limited on how these systems compare with ICM and CF in altering soil nitrogen fractions over time and how these changes are linked to soil biological properties. Evidence is scarce on how these systems influence the seasonal redistribution of nitrogen among inorganic, hydrolysable and non-hydrolysable pools under semi-arid rainfed intercropping. We hypothesized that management practices promoting biological activity and organic matter accumulation would enhance nitrogen retention and improve nutrient cycling. To test this hypothesis, an experiment was conducted in the semi-arid region of India, under a sorghum+blackgram intercropping system to compare different crop management systems with and without Ghanajeevamrut , Beejamrut , and mulching (GBM). Soil nitrogen fractions and biochemical properties were monitored during crop growth and related to productivity. Here we show that organic amendments improved soil biological properties and nitrogen dynamics. Organic systems with GBM achieved a 5-6% gain in available nitrogen, whereas conventional farming showed an 11% decline. OF + GBM recorded the highest microbial biomass carbon (155.08 mg kg - ¹) and peak urease activity (20.75 μg NH 4 + -N g - ¹ h - ¹ at 60 DAS). At harvest, OF + GBM recorded the highest hydrolysable amino acid-N (321.67 mg kg - ¹) and non-hydrolysable N (738.27 mg kg - ¹). ICM recorded the highest nitrate-N (23.57 mg kg - ¹), whereas OF recorded the highest ammonium-N (36.37 mg kg - ¹) at harvest. Redundancy analysis explained 89.14% of the variance and identified microbial biomass carbon and soil organic carbon showing strong associations with active nitrogen fractions. These findings suggest that adding GBM to organic or integrated crop management can strengthen nitrogen cycling and provide a sustainable alternative to conventional farming in semi-arid rainfed agroecosystems.