The Impact of Fulvic Acids on Cotton Growth, Yield and Phosphorus Fertilizer Use Efficiency Under Different Phosphorus Fertilization Rates in Xinjiang, China

Chemical phosphorus (P) fertilizer is often overused in arid regions with alkaline soils due to soil fixation. Fulvic acid (FA) can increase soil P availability, enhancing crop yield and P use efficiency, but its interaction with P fertilization rates and potential to reduce P fertilizer application remains unclear. A 2-year (2019–2020) field experiment was conducted in Xinjiang, China, to study the impact of FA addition (45 kg ha−1) on cotton 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, P uptake and seed cotton yields by 17–37%, but the partial nutrient balance (PNB), agronomic efficiency (AE) and partial factor productivity (PFP) decreased with increasing P fertilization rates. FA addition did not change cotton biomass and P uptake, but significantly enhanced seed cotton yield, AE and PFP by increasing bolls per plant. No significant interactions between FA addition and P fertilization rates were observed for cotton biomass, P uptake, seed cotton yield and P use efficiencies. These findings suggest that FA can improve cotton productivity, AE and PPF of P fertilizers, helping to keep the P balance in the cotton field.