| Summary: | The increased spring rainfall intensity and amounts observed recently in the US Midwest poses additional risk of nitrate (NO _3 ) leaching from cropland, and contamination of surface and subsurface freshwater bodies. Several individual strategies can reduce NO _3 loading to freshwater ecosystems (i.e. optimize N fertilizer applications, planting cover crops, retention of active cycling N), but the potential for synergistic interactions among N management practices has not been fully examined. We applied portfolio effect (PE) theory, a concept originally developed for financial asset management, to test whether implementing multiple N management practices simultaneously produces more stable NO _3 leaching mitigation outcomes than what would be predicted from implementing each practice independently. We analyzed simulated data generated using a validated process-based cropping system model (APSIM) that covers a range of soils, weather conditions, and management practices. Results indicated that individual management practices alone explained little of the variation in drainage NO _3 loads but were more influential in the amount of residual soil NO _3 at crop harvest. Despite this, we observed a general stabilizing effect from adopting well-designed multi-strategy approaches for both NO _3 loads and soil NO _3 at harvest, which became more pronounced in years with high spring rainfall. We use the PE principle to design multi-strategy management to reduce and stabilize NO _3 leaching, which resulted in 9.6% greater yields, 15% less NO _3 load, and 61% less soil NO _3 at harvest than the baseline typical management. Our results make the case for applying the PE to adapt NO _3 leaching mitigation to increased climate variability and change, and guide policy action and on-the-ground implementation.
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