An optimum combination of irrigation amount, irrigation water salinity and nitrogen application rate can improve cotton (for fiber) nitrogen uptake and final yield

Abstract

In some arid regions, the complex planting environment creates higher requirements in terms of cotton planting field management. In order to make a reasonable strategy to utilize underground saltwater resources, save irrigation water and reduce the excessive application of nitrogen fertilizer , we carried out a field experiment in Xinjiang. This study is conducted to explore the effects of irrigation water quantity, irrigation water salinity , and nitrogen application rate on nitrogen fertilizer absorption and cotton yield. Here, three experimental factors and four levels were used in the experiment. Irrigation amounts: 0.7, 1.0, 1.3 and 1.6 ETc; irrigation water salinity: 10.9, 7.8, 4.7, 1.5 dS m −1 ; nitrogen application: 100, 200, 300 and 400 kg N ha −1 were set in the experiment. The experiment was designed according to orthogonal table L 16 (4 3 ). The results showed that the salinity of irrigation water had no effect on soil nitrogen transport, and the soil nitrogen content increased with the increase in nitrogen application. A low level of irrigation increased the lateral migration of nitrogen, whereas excessive irrigation increased the migration of nitrogen to deep soil. When the ratio of irrigation amount (mm) and nitrogen application (kg N ha −1 ) was 2.77, it could ensure the uniform distribution of nitrate nitrogen, and made nitrogen accumulate in the soil layer around the crop root zone . High irrigation increased the nitrogen uptake of the whole cotton plant; however, excessive irrigation would cause the apical dominance of cotton, such that the accumulation of dry matter and nitrogen migration were mainly concentrated in cotton roots and stems, which was not conducive to the migration of nitrogen to the boll (boll shell, seed and fiber). The combination of 675 mm, 7.8 dS m −1 , and 400 kg N ha −1 was more conducive to the migration of nitrogen to the cotton boll. Through principal component analysis, 675 mm irrigation amount, 1.5dS m −1 , and 200 kg N ha −1 is the most recommended irrigation and fertilization strategy. When the irrigation water salinity drops to 7.8 dS m −1 , salt stress can be alleviated by increasing the nitrogen application to 400 kg N ha −1 . • The interaction of irrigation amount and nitrogen application rate greatly affected the soil nitrate nitrogen content. • The ratio of irrigation amount (mm) and N application (kg N ha −1 ) of 2.77 can ensure the uniform distribution of nitrate-N. • Excessive irrigation will cause the apical dominance of cotton and also can decrease productivity. • A combination of 675 mm, 7.8 dS m −1 , and 400 kg N ha −1 was found more favorable for the migration of N to the cotton boll.