Effects of combined application of organic and inorganic fertilizers and fulvic acid on cotton yield, quality and soil fertility under deficit irrigation

To investigate the effects of irrigation amount, combined application of organic and inorganic fertilizers, and fulvic acid (FA) on soil and cotton, a full factorial experiment was conducted with three irrigation levels: 4,500 (W1), 3,825 (W2), and 3,150 (W3) m³/hm²; three levels of combined application of organic and inorganic fertilizers: 0% (O1), 15% (O2), and 30% (O3) organic fertilizer substituting inorganic fertilizer with equal nitrogen; and two FA levels: no FA application (F1) and 45 kg/hm² FA application (F2). Results showed that under the same irrigation amount and combined application of organic and inorganic fertilizers, FA application increased soil water storage at the seedling stage but decreased it at the flowering-boll stage compared with the no-FA treatment. The interaction between irrigation amount and FA exhibited a threshold effect on soil water storage and organic matter content. For O1 and O2 treatments, FA addition increased boll dry matter accumulation by 22.51% and 23.69% respectively, while it reduced by 25.57% in the O3 treatment. Under the O3 condition, FA application improved cotton yield, partial factor productivity (PFP), and irrigation water use efficiency (IWUE) in W1 and W2 treatments, but decreased these indices in the W3 treatment.A comprehensive evaluation was performed via the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS), identifying W1O2F2 as the optimal irrigation and fertilization strategy for yield and efficiency enhancement. In arid and semi-arid regions, W2O1F2, W2O2F2, and W3O3F1 could also achieve the goals of water conservation, stable yield, and efficiency improvement. The results provide a theoretical basis and data support for water-saving and high-efficiency cotton cultivation in Xinjiang and other arid-semi-arid areas.