Improving cotton productivity and nitrogen use efficiency through late nitrogen fertilization: Evidence from a three-year field experiment in the Xinjiang

Context: Premature senescence is a major concern for crop production especially for high -density cotton in Xinjiang, China, when nitrogen (N) rates are reduced. This study aimed to examine the potential of late N fertilization in mitigating senescence, improving light and N use efficiency, and enhancing cotton productivity under reduced N rate. Methods: A three-year field experiment was conducted from 2019 to 2021, employing a total of 240 kg N ha -1 , which was one-third lower than the traditional rate of 360 kg ha -1 . Five different N application ratios based on cotton stages were tested, with N 064 (0:6:4 ratio at early: middle: late growth stages) representing late N fertilization, and N 262 representing traditional ratio in fertilization. The effects of N application timing -based ratios on yield components, N use efficiency, canopy photosynthesis, and root traits were evaluated. Results: The results showed that N 064 had the highest lint yield 2727-3305 kg ha -1 (2019-2021) among all treatments over the three years. Late N fertilization (N 064 ) resulted in significant increases in boll density (4.6-10.7%), seed cotton yield (5.8-8.1%), and N use efficiency (10.5-14.1%) when compared to traditional N 262 . During late peak boll -setting to boll opening stages, N 064 decreased leaf area index (3.5-6.6%), canopy light interception rate (3.8-11.4%), and boll capacity of root (18.1%) compared to N 262 , while increasing SPAD (2.3-4.8%), diffuse non-interceptance (3.9-16.6%), canopy apparent photosynthetic rate (13.2-49.4%), root biomass (19.5%), root/shoot ratio (15.0%). N 064 also resulted in a higher root surface area density in deep soil than N 262 . Conclusions: Late N fertigation enhanced post -flowering canopy photosynthetic production by improving the cotton root -shoot relationship and delaying root and canopy senescence, resulting in improved yields and N use efficiency. This N management strategy implemented under reduced N cultivation shows promise for sustainable cotton production in Xinjiang and similar ecological regions.