Improving the environmental and economic sustainability of citrus orchard systems through optimization of fertilization and organic carbon amendment

Excessive fertilization (NPK) and the depletion of soil organic carbon (C) have become growing concerns in subtropical orchard production, posing a threat to agricultural sustainability. To address these challenges, an integrated soil nutrient management strategy is crucial. Using pomelo orchard as a case, a two-year field experiment was conducted with three treatments, i.e., FP (NPK fertilizer overused), OPT (balanced NPK fertilization), and OPT + C (balanced NPK with organic amendments). The aim was to assess the potential benefits of balancing nutrient inputs and incorporating organic amendments for enhancing efficiency and quality production. The results revealed that, compared to the FP treatment, the OPT treatment significantly reduced environmental footprints: 92.7% for carbon, 85.4% for nitrogen, and 99.9% for phosphorus, while simultaneously improving the benefit-cost ratio by 80.8%. Furthermore, the OPT + C treatment outperformed the OPT treatment by improving fruit yield (by 8.7%) and fruit quality, as indicated by the lowest titratable acidity (0.62%) and highest vitamin C content (403.2 mg kg−1). Structural equation modeling revealed that balanced NPK fertilization improved root morphology, achieving a synergistic balance between economic and environmental efficiency while maintaining pomelo yield. Additionally, organic amendments positively influenced soil properties and enzyme activities, promoting a synergistic increase in both pomelo yield and quality. In conclusion, the combination of balanced NPK and organic amendments led to synergistic improvements in pomelo yield, fruit quality, environmental footprints, and benefit-cost ratio. These findings provide a valuable framework for improving orchard efficiency and quality production through an integrated soil nutrient management strategy.