Optimum nitrogen application rate improves the accumulation of nitrogen, phosphorous and potassium and lint yield of cotton

Objectives Nitrogen supply is necessary for the rapid and healthy growth of cotton, however lint cotton production is sensitive to excessive N supply. We investigated the appropriate nitrogen (N) application rates for efficient lint cotton production and nutrient absorption, to provide theoretical basis for efficient yield and nutrient management of cotton.

Methods  A field experiment with split-plot design was conducted in 2019 and 2020 in Anyang, Henan Province.The main plot was N application rate: 0, 60, 120, 180, 240, 300, and 360 kg/hm²; the sub-plot was two cotton cultivars, Jimian228 (middle maturity) and Lumianyan28 (mid-early maturity), which were the main high-yielding cultivars grown in the areas of the Yellow River Valley. The shoot biomass, yield, and above ground N, P and K contents were determined.

Results The shoot biomass of Jimian228 increased significantly with the increase of N application rates from 0 to 240 kg/hm², but was not affected by N application rates which exceeded 240 kg/hm². The shoot biomass of Lumianyan28 started decreasing when N application rates exceeded 180 kg/hm². N application significantly increased the accumulation of N, P, and K in the shoots of Jimian228 and Lumianyan28. The increment for Jimian228 were 37.5%, 23.5%, and 29.2%, where as for Lumianyan28, it was 47.2%, 34.0% and 35.5%, respectively, and Lumianyan28 was higher than in Jimian228. The increase of shoot biomass and NPK concentent contributed 65.9%–82.4% and 17.6%–34.1% to the increase of N, P and K accumulation in cotton shoot. The boll number per plant of Jimian228 and single boll weight of Lumianyan28 initially increased and then decreased with increasing N application rates. Simulated with a linear-plateau model, the optimal N application rates for the two cultivars were 180 kg/hm² and 188 kg/hm², which corresponded with lint yield of 1661 kg/hm² and 1538 kg/hm², respectively. The lint production efficiency of N, P and K generally decreased significantly with increasing N application rates. The lint production efficiency of P and K showed significantly positive relationship with that of N. The yield harvest index was negatively correlated with the accumulation of N, P and K, but positively correlated with the harvest index of N, P and K, indicating that it can be used as an indirect index of fertilizer use efficiency.

Conclusions N application increased NPK contents and the dry matter of cotton shoot, both NPK content and dry matter brought about enhanced shoot NPK accumulation, with the contribution rate of 65.9%–82.4% by dry matter and 17.6%–34.1% by higher NPK content. The lint cotton production efficiency of N was closely related to that of P and K. Therefore, N application could stimulate the absorption and utilization of P and K. Under conditions similar to the study area, the optimal N application rate for high yield and high use efficiency of nutrient for Jimian 228 and Lumianyan 28 are 180 and 188 kg/hm², respectively.