Economic competitiveness of separated dairy manure solids as a phosphorus fertilizer substitute

Manure solid-liquid separation offers a potential pathway for redistributing nutrients from livestock-intensive, nutrient-surplus regions to cropland with fertilizer demand, but the competitiveness of separated manure products with synthetic phosphorus fertilizer depends on manure quality, acquisition price, and hauling distance. We developed a probabilistic techno-economic framework to evaluate separated dairy manure solids (SDMS) relative to synthetic phosphorus fertilizer under representative market and agronomic conditions and to identify transaction-level thresholds for competitive viability. The analysis combined Sobol global sensitivity analysis, Monte Carlo uncertainty propagation, deterministic scenario surfaces, and leverage analysis. SDMS acquisition price was the dominant driver of variance in net savings, followed by P₂O₅ concentration and hauling distance. Competitiveness declined sharply with transport distance, with the 50% probability crossover occurring between 161 and 201 km and the most decision-sensitive range concentrated around 121-201 km under the modeled conditions. Scenario analysis showed that lower acquisition price and higher P₂O₅ concentration substantially expanded the viable hauling radius, while moisture reduction also improved competitiveness but with different marginal returns across the quality surface. The leverage surface showed that the relative benefit of dewatering versus P₂O₅ enrichment depends on the current product state; across much of the evaluated commercial range, a 1 percentage point reduction in moisture produced a greater gain in breakeven hauling distance than a 0.1 percentage point increase in P₂O₅ concentration, although the reverse held at low P₂O₅ concentrations combined with low moisture. The results also identified an acquisition-price ceiling beyond which additional processing no longer preserved competitiveness. These findings provide transaction-level economic criteria for manure redistribution and are implemented in NutrientChoice (https://www.dairyconservation.org/NutrientChoice), an open-source decision-support tool.