A multi-level integration framework for sustainable nitrogen management in tropical agriculture

Nitrogen(N)lossandinefficiencythreatenbothfoodsecurityandenvironmentalsustainabilityintropicalagriculture. Despite growing N inputs, many tropical systems suffer from low N use efficiency (NUE) and high pollution due to poor management. Aligning agricultural productivity with environmental safety remains a major challenge, given the lack of integrated, context-specific decision-support approaches. Here, we present a systematic multi-level integration framework to assess the N carrying capacity required to meet crop productivity while staying within safe N surplus limits, enabling a hierarchy of strategic interventions— including N fertilizer quotas, 4R-plus stewardship, and integrated crop-livestock systems. Using Hainan Island, China, as a representative case, we demonstrate that achieving N carrying capacity, target NUE levels, and halving N losses requires combining optimized cropland management with enhanced internal nutrient recycling. Scenarioanalysis showsthatintegratedstrategiescanincreaseNUEbyupto26percentagepoints (from 23% to 49%) andreduce synthetic N input by nearly 50%. This work offers a scalable pathway to supportevidence-basedtechnologicalandpolicysolutionsforsustainableNmanagementintropicalagriculture.