Modelling Cotton Growth Dynamics, Yield, and Water Use Efficiency in Xinjiang Agricultural Systems

Cotton (Gossypium hirsutum L.) yield (Y) generally depends on the plant height (H), leaf area index (LAI), dry matter accumulation (D), and water consumption (W) of the entire growing period. Growing degree days (GDD) is an important meteorological factor affecting these growth indicators. This paper establishes a relative logistic growth model of H, LAI and D based on relative growing degree days (R_GDD) and analyses the spatial variability characteristics of the model parameters. The influence degree of model parameters on Y, W and harvest index (HI) are determined using the grey relational analysis. A series of cotton mathematical models are then proposed based on maximum LAI (LAI_max) and W. The results reveal that the growth rates of cotton H, LAI and D were maximised when the R_GDD is 0.43, 0.56 and 0.67, respectively. The coefficient of variation of the model parameter ranges from 0.1 to 1.0, indicating medium variability. The cotton HI and Y reach maximum values of 0.343 and 7236.464 kg/ha for LAI_max values of 5.046 and 5.949 cm²/cm², respectively. The corresponding required water consumption (W) is determined as 489.606 mm and 497.978 mm, while the water use efficiency (WUE) is 14.686 kg/(ha·mm) and 14.532 kg/(ha·mm), respectively. Furthermore, the cotton LAI_max and W range from 2.719 to 7.225 cm²/cm² and 455.957 to 642.688 mm, respectively. This study provides a scientific foundation for enhancing Y and WUE in the agricultural regions of Xinjiang. Furthermore, the proposed methods enable the prediction of Y and WUE with improved accuracy.