Abstract:
To investigate the effect of nitrogen reduction with humic acid application on island cotton plants and soil nutrients, in 2022−2023, a one-factor randomized block trial was conducted with Island Cotton ‘New 78’ as the material, five treatments were set up: no nitrogen application (CK), normal nitrogen application of 600 kg·hm
−2 (OF
1), reduced nitrogen application of 50% (300 kg·hm
−2, OF
2), and reduced nitrogen application of 300 kg·hm
−2 + humic acid 150 kg·hm
−2 (OF
3), and humic acid 300 kg·hm
−2 (OF
4), to analyze the effects of nitrogen reduction and humic acid on dry matter accumulation, nitrogen, phosphorus and potassium accumulation and distribution, soil nutrients and yield quality of island cotton plants. The results showed that: Reducing nitrogen application combined with humic acid effectively promoted dry matter accumulation and optimized dry matter distribution in island cotton. Among them, OF
3 exhibited the highest dry matter accumulation, with a two-year average significantly higher than CK, OF
2, and OF
4 by 27.58%, 19.81%, 12.99%, respectively, while showing no significant difference compared to OF
1. OF
3 could effectively promote the transport of nutrients to reproductive organs, and the distribution proportion gradually increased with the progress of the growth period. The two-year average accumulation was significantly increased by 25.07% compared with CK, and there was no significant difference from OF
1. Nitrogen reduction and humic acid application could significantly increase the accumulation of total nitrogen, total phosphorus and total potassium in island cotton plants, and promote the allocation of nitrogen, phosphorus and potassium accumulation to reproductive organs. At the bolling and flocculation stages, the accumulations of total nitrogen, total phosphorus and total potassium in OF
3-treated plants were significantly higher than those in CK, although the accumulations of total nitrogen were slightly lower than those in OF
1, but the differences were not significant. OF
3 could promote the allocation of nutrients from the Island cotton plants to the reproductive organs, and the proportion of total nitrogen, total phosphorus and total potassium to reproductive organs was the highest during the flocculation stage, with the percentages of total nitrogen, total phosphorus and total potassium being 63.65%, 62.95% and 59.69%, respectively. Nitrogen reduction with humic acid can significantly increase soil organic matter and alkaline nitrogen content. During the flowering and fluttering periods, soil organic matter content was highest in OF
4 and second in OF
3; soil alkaline nitrogen content was highest in OF
1 and second in OF
3; soil available P and available K content was highest in OF
3 and second in OF
4. In addition, nitrogen reduction with humic acid not only improves the yield of island cotton, but also keeps the fiber quality of island cotton at a high level. In the 2-year experiment, the average seed cotton yield of OF
3 reached 6 581.15 kg·hm
−2, which was 36.91%, 4.36%, 11.57%, and 18.85% higher than that of CK, OF
1, OF
2, and OF
4, respectively. The average breaking tenacity improved by 3.35%, 1.31%, and 3.79% compared to CK, OF
2, and OF
4, respectively, the average micronaire value was improved by 8.75%, 2.23% and 8.37% compared with CK, OF
2 and OF
4, respectively, and there was no significant difference in all fiber quality parameters between OF
3 and OF
1. Therefore, the fertilization strategy of applying 300 kg·hm
−2 of nitrogen + 150 kg·hm
−2 of humic acid in the production of the main production area of island cotton in Xinjiang can significantly increase the nitrogen, phosphorus and potassium accumulation of island cotton plants, improve the content of soil organic matter and quick-acting nitrogen, and obtain a higher seed cotton yield, in order to achieve the dual goals of efficient use of nitrogen fertilizer and yield enhancement.