Soil-Specific Nitrogen and Phosphorus Leaching Patterns of Recovered Nutrients

Products obtained from livestock manure and anaerobic digestion are increasingly promoted as alternatives to conventional mineral fertilisers. However, their environmental performance depends on fertiliser characteristics and soil properties controlling nutrient mobility. This study evaluated nitrogen (N) and phosphorus (P) leaching dynamics following the application of pig slurry, digestate, and ammonium sulphate recovered through digestate stripping. Replicated soil column experiments were conducted using four agricultural soils from three European river basins (Ebro, Lielupe and Danube), three fertiliser treatments, and three replicates per treatment, under controlled climatic conditions (15–25 °C; 50–60% relative humidity; 16 h light/8 h dark cycle) reproducing field climate and water application regimes. Leachates were periodically collected and analysed for ammonium (NH4+-N), nitrate (NO3−-N), and phosphate (PO43−-P). Results showed distinct nutrient release and transport patterns among fertilisers and soils. Ammonium sulphate produced rapid NH4+-N losses immediately after application, whereas digestate and pig slurry exhibited a more gradual nutrient release. The relative contribution of ammonium and nitrate to total N leaching varied among soils, highlighting the influence of soil properties on nitrification and nutrient retention processes. Phosphorus losses remained low across treatments. These findings support nutrient recovery strategies adapted to soil conditions to enhance nutrient circularity while minimizing environmental losses. In practical terms, managers and policymakers should require soil-specific nutrient management plans for recovered fertilisers, prioritising slow-release products such as digestate or pig slurry on soils prone to nitrogen leaching, and restricting ammonium sulphate to soils with lower leaching risk.