Fulvic Acid Enhances Cotton Yield and Phosphorus Use Efficiency Under Different Application Rates of Phosphorus Fertilizers

Chemical phosphorus (P) fertilizer is often overused in arid regions with alkaline soils due to soil fixation. Fulvic acid (FA) has been reported to increase soil P availability, thus enhancing crop growth, yield and P use efficiency, but its interaction with P fertilization rates and potential to reduce P fertilizer application remains unclear. In this study, we conducted a 2-year (2019-2020) field experiment in Xinjiang, China, to study the impact of FA addition on cotton (Gossypium hirsutum) growth, yield and P use efficiency under different P fertilization rates (0, 50, 100, and 150 kg P2O5 ha-1). Our results showed that P fertilization significantly enhanced cotton biomass and seed cotton yields by 15-41%, mainly attributed to an increased emergency rate. Accordingly, soil Olsen-P levels increased by 7-22% with P fertilization. Partial nutrient balance, agronomic efficiency and partial factor productivity decreased with increasing P fertilization rates. Across all P fertilization rates, FA addition significantly increased soil Olsen-P levels by 6% in 2019, but not in 2020, and enhanced seed cotton yield through increasing bolls per plant in both years. In 2020, FA addition significantly improved the agronomic efficiency and partial factor productivity of P fertilizer, but did not affect apparent recovery efficiency and partial nutrient balance. No significant interactions between FA addition and P fertilization rates were observed for soil Olsen-P, cotton biomass, P uptake, yield and P use efficiency. These findings suggest that FA can improve cotton productivity by increasing soil P availability, and use efficiency of P fertilizers, irrespective of application rates. Therefore, FA addition is an effective strategy for cotton production in arid regions for optimizing P fertilization rates and improving seed cotton productivity.