Construction, validation, and nitrogen nutrition diagnosis of a critical nitrogen concentration model for cotton

Yukun Qin¹Feng Weina²Junying Chen¹Cangsong Zheng²Yingshu Leng¹Lixian Wang¹Lijuan Zhang^1*Taili Nie^1*

• ¹江西省经济作物研究所, 九江市, China
• ²Chinese Academy of Agricultural Sciences State Key Laboratory of Cotton Bio-breeding and Integrated Utilization, Anyang, China

Based on continuous field experiments in Jiujiang City, Jiangxi Province, a critical nitrogen concentration dilution curve model for different parts of cotton in the rapeseed cotton rotation pattern in the Yangtze River Basin was constructed. The nitrogen nutrient index (NNI) was used to diagnose the nitrogen abundance and deficiency status, providing a basis for precision fertilization management in cotton fields. A randomized block design was used and six nitrogen application treatments were set up. The dry matter mass and nitrogen content of each organ of cotton were measured during the initial flowering stage, peak flowering stage, peak boll stage, and boll opening stage in 2023 and 2024, respectively. A critical nitrogen concentration dilution curve model based on whole plant nitrogen content and reproductive organ nitrogen content was constructed using 2023 data. The model was validated using 2024 data to compare the nitrogen nutrition diagnostic effects of the two models. The results showed that the critical nitrogen concentration dilution curve models based on cotton whole plant and reproductive organ biomass (represented by y1 and y2 respectively) were constructed as follows: y1=26.936x-0.284(R2=0.6800, P<0.05), y2=23.504x-0.226(R2=0.6226, P<0.05), the RMSE were 2.76 and 3.53 respectively, with nRMSE of 15.10% and 14.85% (both within the range of 10% to 20%), indicating that the model accuracy had reached a good level or above. The nitrogen nutrition index based on the whole plant and reproductive organ (represented by NNI1 and NNI2 respectively) showed a significant positive correlation with seed cotton yield (P<0.05), and a "linear+plateau" relationship with RY (relative yield) (RY=1.4879NNI1-1.0095 (R2=0.6434*), RY=0.9461NNI2-0.3723 (R2=0.6165*). When the two NNIs reached 1.22 and 1.17, respectively, RY reached its peak. When nitrogen application reached 240 kg.ha-1, both NNI values could stably reach 1 or above from the initial flowering stage to the boll opening stage, and showed significant advantages in multiple dimensions such as biomass accumulation, yield performance, fiber quality, and nitrogen fertilizer use efficiency. The critical nitrogen concentration dilution curve model based on reproductive organ nitrogen content and the nitrogen nutrition diagnosis model had the advantages of being more labor-saving and efficient while maintaining the same level of accurate diagnosis.