Improving cotton productivity and nutrient use efficiency by partially replacing chemical fertilizers with organic liquid fertilizer under mulched drip irrigation

Soil degradation and associated environmental problems caused by the excessive use of fertilizers are the main challenges in agricultural production in arid or semiarid areas. The partial substitution of chemical fertilizer with organic manure fertilizer is an important measure for reducing fertilizer usage and improving agricultural production efficiency. We hypothesized that integrated water and fertilizer application under mulched drip irrigation and the optimization of organic liquid fertilizer (OLF) and chemical fertilizer application can result in the regulation of spatiotemporal differences in soil nutrient supply and cotton nutrient absorption efficiency and allow for simultaneous increases in cotton yield and fertilizer use efficiency. To test this hypothesis, three fertilization treatments were employed: no fertilizer (CK), chemical fertilizer (CF), and organic liquid fertilizer (OLF) combined with chemical fertilizer at five different ratios, with F0.6, F0.8, F1.0, F1.2, and F1.4 corresponding to 0.6, 0.8, 1.0, 1.2, and 1.4 of CF, respectively. In this paper, the effects of organic liquid fertilizer combined with chemical fertilizer application on soil nutrient content, dry matter accumulation, nutrient uptake, yield and fertilizer utilization efficiency were investigated through two years of field experiments. Our results demonstrated that compared to chemical fertilizer treatment, combined OLF and chemical fertilizer application in the F0.8 treatment substantially increased soil organic matter content by an average of 13.4% in shallow soils (0–20 cm) without affecting nitrate nitrogen, quick-acting phosphorus or quick-acting potassium levels. Furthermore, in the F0.8 treatment, a remarkable decrease in Mn and Fe content was observed in shallow soils (0–20 cm, wide rows), while Cu and Zn content significantly increased in the 40–100 cm soil layers (narrow rows). Compared with the CF treatment, this combined application strategy substantially enhanced the uptake of nitrogen (N), phosphorus (P2O5), and potassium (K2O) in cotton plants, with average increases of 7.8−45.0%, 4.9−35.0%, and 6.0−25.0%, respectively. Additionally, it shortened the N and P2O5 rapid accumulation duration and increased the rate of accumulation by an average of 25.0∼37.0%, facilitating efficient nutrient transfer to cotton bolls. OLF combined with chemical fertilizer application significantly increased the efficiency of nitrogen and phosphorus fertilizer use in cotton. Moreover, seed cotton yield in the combined treatments increased by an average of 3.7–26.7% compared to that in the CF treatment, and the greatest increase was found in the F0.8 treatment. Overall, our findings suggest that in mulched drip irrigation systems, OLF with chemical fertilizer application can enhance soil organic matter content and nutrient availability, optimize nutrient uptake and distribution in cotton plants, and improve seed cotton yield and nutrient use efficiency.