| Summary: | Abstract Background An optimal N rate is one of the basic determinants for high cotton yield. The purpose of this study was to determine the optimal N rate on a new cotton cropping pattern with late-sowing, high density and one-time fertilization at the first flower period in Yangtze River Valley, China. A 2-year experiment was conducted in 2015 and 2016 with a randomized complete block design. The cotton growth process, yield, and biomass accumulation were examined. Results The results showed that N rates had no effect on cotton growing progress or periods. Cotton yield was increased with N rates increasing from 120 to 180 kg·hm−2, while the yield was not increased when the N rate was beyond 180 kg·hm−2, or even decreased (9∼29%). Cotton had the highest biomass at the N rate of 180 kg·hm−2 is due to its highest accumulation speed during the fast accumulation period. Conclusions The result suggests that the N rate for cotton could be reduced further to be 180 kg·hm− 2 under the new cropping pattern in the Yangtze River Valley, China.
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