Fulvic acid-amino acid organic fertilizer: Optimal co-application, sustainable remediation, and yield improvement strategies for aline-alkaline cotton fields in Xinjiang

Saline-alkali soils in Xinjiang significantly limit the sustainable development of the local cotton industry. While previous studies have demonstrated that individual applications of fulvic acid or amino acid organic fertilizers effectively improve soil quality and increase crop yield, the combined effects of their co-application on cotton remain insufficiently understood. To address this knowledge gap, this study aimed to conduct a comprehensive two-year field experiment employing a factorial design with three fulvic acid application rates (50, 75, and 100 kg ha–1, designated as A1–A3) and three amino acid application rates (0, 750, and 1500 kg ha–1, designated as B1–B3). The objective of this study was to systematically evaluate the combined effects of these organic amendments on soil physicochemical properties, cotton productivity, fiber quality, and economic viability in saline-alkali cotton fields in this region. The results revealed that, compared to the control, organic fertilizers significantly enhanced soil properties. In the 0–40 cm layer, soil water content, porosity, microbial biomass carbon, microbial biomass nitrogen, total phosphorus, nitrogen, organic carbon, nitrate nitrogen, and ammonium nitrogen increased, while the bulk density, soil salinity, and pH decreased. Cotton yield and fiber quality peaked under the A3B3 treatment, closely followed by the A3B2 treatment. A comprehensive evaluation of soil quality, cotton fiber quality, and profit identified the A3B2 treatment as the optimal fertilization strategy. These findings provide valuable insights for the development of sustainable soil management practices in the saline-alkali cotton production systems of Xinjiang and similar saline-alkali areas.