Rock phosphate enriched pressmud compost: A valorized agro-industrial amendment for enhancing phosphorus use efficiency in high-value field crops

Low phosphorus (P) use efficiency of conventional mineral fertilizers underscores the need for resource-efficient P management strategies. Rock phosphate enriched pressmud compost (RPEPC) offers a potential approach for recycling sugar-industry by-products while providing a gradual P supply. However, its capacity to partially substitute mineral P fertilizer remains inadequately evaluated with respect to crop productivity, P use efficiency, P balance, soil fertility, and economic viability. Therefore, a field experiment was conducted to evaluate RPEPC as a P source in maize–wheat and soybean–wheat cropping systems. Partial substitution of diammonium phosphate (DAP) with RPEPC (50% and 75%) enhanced maize and wheat productivity, while maintaining yields comparable to sole DAP application in the soybean–wheat system. Phosphorus-use efficiency increased by approximately 1.79- to 3.01-fold under the integrated treatments. Relative to sole DAP, combined application of RPEPC and DAP increased soil organic carbon by 10.0–22.4%, mineralizable nitrogen by 10.9–22.4%, available potassium by 5.4–21.5%, Olsen P by 56.6–87.5%, and organic P by 10.3–33.5% across soil depths (0–15 and 15–30 cm) and sampling years (2023 and 2025). Across both cropping systems, the 50% RPEPC + 50% DAP treatment produced the highest net returns (USD 2227 and 2130 ha −1 , respectively) and net benefit–cost ratios (0.94 and 0.95, respectively), outperforming the sole fertilizer and compost treatments. Overall, the partial substitution of mineral DAP with RPEPC sustained or enhanced crop productivity, P-use efficiency, soil fertility, and economic performance, demonstrating its potential as a circular P management strategy linking sugar-industry waste valorization with sustainable crop production.