Effects of nitrogen reduction combined with humic acid application on island cotton plant and nutrient utilization

Explore the effects nitrogen reduction combined with humic acid application on the nutrient status of island cotton plants and soil, providing a scientific basis for rational fertilization in the main production areas of island cotton in Xinjiang. The study was conducted from 2022 to 2023 using the island cotton variety 'new 78' as the experimental material. Five treatments were established: no nitrogen (CK), normal nitrogen 600 kg·hm^-2(OF₁), reduced nitrogen 300 kg·hm^-2(OF₂), reduced nitrogen 300 kg·hm^-2 + humic acid 150 kg·hm^-2 (OF₃) and humic acid 300 kg·hm^-2(OF₄). The impacts of different fertilization methods on dry matter accumulation, the accumulation and distribution of nitrogen, phosphorus, and potassium, soil nutrient levels, yield, and quality in island cotton fields were analyzed. The results showed that nitrogen reduction combined with humic acid could effectively promote dry matter accumulation and optimize its distribution in island cotton. The average annual dry matter accumulation under OF₃ treatment was the highest, exceeding that of CK, OF₁, OF₂, and OF₄ by 25.07%, 1.51%, 16.31% and 12.37%, respectively. OF₃ facilitated the transfer of nutrients to the reproductive organs, resulting in a gradual increase in the distribution proportion of these organs, the annual accumulation increased by 26.61% compared to CK, which was not significantly different from OF₁. This combination approach also significantly enhanced the accumulation of total nitrogen, total phosphorus and total potassium in island cotton plants, and promoted the distribution of these nutrients to the reproductive organs. In plants treated with OF₃, the total nitrogen, total phosphorus, and total potassium accumulation were significantly higher than those in CK. Although total nitrogen accumulation was slightly lower than OF₁, the difference was not significant.OF₃ promotes the distribution of nutrients from island cotton plants to the reproductive organs, with the proportions of total nitrogen, total phosphorus and total potassium in these organs being the highest at 63.65%, 62.96% and 59.69%, respectively. The combination of nitrogen reduction combined with humic application significantly increase the content of soil organic matter and alkali-hydrolyzed nitrogen. During the flowering and boll formation stage, the highest soil organic matter content is observed in OF₄ , followed closely by OF₃. OF₁ exhibits the highest content of soil alkali-hydrolyzed nitrogen, with OF₃ ranking second. The highest levels of soil available phosphorus and potassium are found in OF₃, followed by OF₄. In addition, the application of nitrogen reduction in conjunction with humic acid not only achieves the highest yield of island cotton, but also maintain a high level of fiber quality. The annual yield and yield components of OF₃ are the best among the treatments, while CK yields the lowest, the annual seed cotton yield under OF₃ reaches 6 581.15kg ·hm^-2, which is 26.96%, 4.36%, 10.37% and 15.86% higher than CK, OF₁, OF₂ and OF₄, compared with CK, OF₂ and OF₄, the average annual fracture specific strength and Maxloon value of OF₃ cotton are 3.35%, 2.43%, 3.79% and 9.13%, 6.94% and 6.94%, respectively, showing no significant difference between OF₃ and OF₁ fiber indexes in two years. Therefore, implementing a fertilization strategy of 300 kg·hm^-2 nitrogen and 150 kg·hm^-2 humic acid in the main production area of island cotton in Xinjiang can significantly increase the accumulation of nitrogen, phosphorus and potassium in island cotton plants, It also increases the content of soil organic matter and available nitrogen, maintains the balance of soil phosphorus and potassium, and results in higher seed cotton yields, thereby achieving the dual objectives of efficient nitrogen fertilizer utilization and yield enhancement.