Managing plant density and nitrogen fertilizer to reduce nitrogen input without yield reduction of late-sown cotton after wheat by improving light interception and sink nitrogen partitioning in a double cropping system

Context: Conventional relay intercropping of cotton in wheat is being replaced by late-sown cotton after wheat to increase wheat output and decrease labor and nitrogen (N) input of cotton with no yield reduction in Yangtze River Valley of China. Objective: However, the mechanistic basis for yield stabilization in a higher plant density with decreased N rate of late-sown cotton from the perspective of light interception and N partitioning has not been evaluated. Methods: A split plot experiment with two planting densities (D1, 6 plants m- 2; D2, 8 plants m-2) as the main plot and three N rates (N1, 150 kg ha -1; N2, 180 kg ha -1; N3, 210 kg ha -1) as the subplot was conducted in Wuhan from 2018 to 2019 to determine their interaction on cotton yield, canopy light interception (CLI), temperatures and humidity, and N partitioning in different sections of the plant. Results: Results showed that a significant interaction of plant density and N rate existed, which indicated that at 8 plants m- 2, N rate could be reduced to 180 kg ha- 1 without yield reduction compared with 210 kg ha -1. CLI at peak bloom stage, the maximal light interception, and the duration of CLI > 70% were increased by 30.1%, 3.5%, and 9.4% at 8 plants m- 2 compared with those at 6 plants m- 2, respectively. However, a lower maximal canopy temperature and relative humidity at flowering under 8 plants m- 2 compared to 6 plants m- 2 was recorded, showing a negative correlation with cotton yield (P<0.05). Cotton had 14.9% and 2.8% higher N uptake and sink N partitioning at 8 plants m- 2 compared to those at 6 plants m- 2, respectively. Thus, N use efficiency at 8 plants m- 2 was increased. Conclusions: A reduction in the rate of N at high plant density increased CLI and sink N partitioning and thus did not reduce yield in late-sown cotton. Implications: Therefore, the optimal seedcotton yield was achieved at 8 plants m- 2 combined with 180 kg N ha -1, which attributed to higher canopy light interception and N utilization in late-sown cotton after wheat harvest.

Automated summary

Conventional relay intercropping of cotton in wheat is being replaced by late-sown cotton after wheat to increase wheat output and decrease labor and nitrogen (N) input of cotton with no yield reduction. However, the mechanistic basis for yield stabilization in a higher plant density with decreased N rate of late-sown cotton from the perspective of light interception and N partitioning has not been evaluated.