Impact of Nitrogen Application Frequency on Cotton Yield and Nitrogen Use Efficiency under Integrated Water-Fertilizer Management

Water-nitrogen (N) coupling is recognized as a crucial strategy for enhancing crop yield and improving nitrogen use efficiency (NUE).However, the specific mechanisms by which the frequency of split nitrogen fertilizer applications influences cotton yield and NUE under water-nitrogen coupling conditions remain poorly understood. To determine optimal N fertilization strategies,a two-year consecutive field experiment was conducted from 2023 to 2024, comparing three treatments: no nitrogen fertilizer (CK), nitrogen fertilizer applied in eight follow-up applications (N8) and nitrogen fertilizer applied in ten split applications (N10). The results indicated that the N8 treatment maintained the highest levels of soil organic matter and alkali-hydrolyzable nitrogen content in the 0 ~ 20 cm soil layer compared with other treatments. When nitrogen application rates were consistent, adjusting the frequency of nitrogen application could improve the distribution of dry matter and nitrogen accumulation in cotton within the Xinjiang cotton-growing region. Specifically, the N8 treatment achieved a balanced relationship between vegetative and reproductive growth, facilitating greater accumulation of dry matter and nitrogen in reproductive organs. In both 2023 and 2024, the N8 treatment increased net photosynthetic rate by 25.27% and 45.21%, transpiration rate by 55.30% and 46.42%, and stomatal conductance by 38.89% and 55.95%, seed cotton yield by 31.94% and 36.78%, nitrogen fertilizer utilization rates by 56.07% and 49.11%, respectively,compared to the CK treatment, while intercellular CO₂ concentrations decreased by 18.76% and 22.91%, respectively. Moreover, cotton seed yield is highly significantly and positively correlated with dry matter accumulation and nitrogen accumulation.Under irrigation under plastic film irrigation, applying N fertilizer in eight doses effectively ensured soil nutrient availability, promoted dry matter and nitrogen in cotton, promote photosynthesis, and thereby enhanced cotton yield.