Sustainable phosphorus management through enriched compost and mineral fertilizers improves soil biological indicators and mustard productivity

Agri-food and nutritional security are increasingly threatened by soil degradation and climate change, which accelerate nutrient depletion and limit sustainable agricultural productivity. Phosphorus (P) availability is often limited by soil fixation, which makes P use efficiency extremely low; therefore, evaluating the influence of different P-sources on soil P-transformations is essential for enhancing P availability and mustard ( Brassica juncea ) productivity. A three-year field experiment was conducted from 2021–22 to 2023–24 during the Rabi season using five treatment combinations in a randomized block design (RBD) with four replications per treatment. Treatments included absolute control (Ct), recommended dose of fertilizers (RDF-100%) supplying N-P 2 O 5 -K 2 O-S fertilizers at 80-40-40-40 kg ha -1 , enriched compost (EC) at 6 Mg ha -1 (EC-6), EC at 6 Mg ha -1 + RDF-100% (EC-6 +RDF-100%) and EC at 6 Mg ha -1 + RDF-50% (EC-6 + RDF-50%). During the study period, major soil P pools i.e ., saloid-P (S-P), iron-associated P (Fe-P), aluminium-associated P (Al-P), and calcium-bound P (Ca-P) increased progressively under all the fertilized treatments compared to the control (Ct). The combined application of EC-6 + RDF-100% resulted in a significant build-up in Olsen-P, total-P (Pt) and inorganic-P (Pi) compared to RDF-100%. EC-6 + RDF-100% had 14, 16 and 15% higher Pt, Pi and organic-P (Po), respectively, during 2023-24 over 2021-22 in comparison to RDF-100%. Walkley Black carbon (WBC) also improved with RDF-100% compared to Ct over the years however, the highest concentration of WBC was observed with EC-6 + RDF-100%. Soil microbial activities were significantly enhanced by the integrated application of compost and mineral fertilizers compared to Ct. Improved P availability and soil microbial activities under EC-6 + RDF-100% treatment resulted in insignificantly higher mean (3 years) mustard seed (2.89 Mg ha −1 ) and stover (4.90 Mg ha −1 ) yield over RDF-100%. Notably, EC-6 + RDF-50% also produced 12% higher mean mustard seed yield over RDF-100%. EC-6 + RDF-100% also resulted in higher P uptake by both mustard seed and stover as compared to RDF-100%. These findings demonstrate that integrating enriched compost (EC-6) with mineral fertilizers (RDF-100%) is an effective strategy to enhance P availability, improve soil biological health, and sustainably increase mustard productivity. • Mustard yield was significantly higher with EC-6 + RDF-100% than RDF-100%. • RDF-100% exhibited the greatest P recovery in seed and stover. • EC-6 + RDF-100% significantly enhanced Olsen-P, total-P and inorganic-P. • EC-6 + RDF-100% improved microbial activity and soil carbon metrics.