Model-based optimal management strategies to mitigate soil acidification and minimize nutrient losses for croplands

Enhanced nitrogen (N) and phosphorus (P) fertilizer applications have strongly elevated agricultural productivity, but also caused significant soil acidification (by N) and increased N and P losses to water bodies leading to eutrophication. There is an urgent need to integrate soil acidification amendment and nutrient management strategies to stimulate sustainable soil use and minimize environmental risks. This study aimed to derive the optimal combination of fertilizer, manure and lime to mitigate soil acidification and minimize nutrient losses by assessing the impacts of different nutrient management strategies on soil pH and nutrient budgets at a field level. The dynamic soil acidification model VSD+ was calibrated on measured pH changes in a long-term fertilization experiment (1990–2018), in which variable amounts of inorganic N, P and potassium (K), lime (L) and organic manure (M) were applied annually to a maize-wheat rotation on red soil. Adding NPK inorganic fertilizers only sharply decreased the soil pH by 1.5 units within 10 years. The pH remained relatively constant, however, in the experiment in which 70% of the N given by fertilizer was replaced by manure (NPKM) while lime addition after 20 years of NPK addition (NPKL) increased the pH by approximately 1.5 units. Historic soil pH changes were well reconstructed by VSD+ . The model quantified that nitrogen transformations contributed up to 89% of the total acidity production in the NPK treatment, which could be fully neutralized by replacing 70% of the total N fertilizer input with manure. Scenarios were assessed to explore the future impacts of adapted nutrient management on soil acidification and nutrient surplus. Balancing the N and P input with crop demand (BNP) significantly reduces the N and P surplus but hardly affects the acidification rate compared to Business as Usual (BAU, equal to the NPK treatment). Balancing the N input and substituting N fertilizer with manure (BM) counteract acidification and maintain the optimal soil pH of 6.5 but strongly increase the annual P surplus. An optimized combination of fertilizer, manure and lime (OPT) was thus identified to minimize acidification and unnecessary P accumulation in soils, by balancing crop N, P and base cation (BC) demands and unavoidable N and BC leaching. We conclude that the VSD+ model can be used as a sustainable nutrient and acid management tool to derive optimal application rates of fertilizer, manure and lime in agricultural systems.