## 2 Materials and Methods  
### Study Site and Experimental Design  
The field experiments were conducted in Daxiqu Town, Changji City, within the Xinjang Uygur Autonomous Region of northwestern China (86\({}^{\circ}\)24\({}^{\prime}\)-87\({}^{\circ}\)37\({}^{\prime}\) E, 43\({}^{\circ}\)06\({}^{\prime}\)-45\({}^{\circ}\)20\({}^{\prime}\) N), at an average elevation of 570 m above sea level (Figure 1). This region lies within the temperate climatic zone and is characterized by a pronounced continental arid climate, marked by extreme seasonal temperature fluctuations. Winters are notably cold, while summers are intensely hot, with significant diurnal temperature variations that are typical of arid inland basins. Detailed meteorological data, including precipitation, temperature, and solar radiation patterns, are provided in Table 1.  
The experimental site is situated on sandy loam soil, as classified by the United States Department of Agriculture (USDA) soil taxonomy. Comprehensive physicochemical analyses of the soil profile, spanning depths from 0 to 100 cm, are presented in Table 2. For the purposes of this study, the soil profile was divided into distinct layers: the shallow layer (10-20 cm) and the deep layer (40-100 cm). These layers were selected to capture variations in soil properties that influence root growth, water retention, and nutrient availability, which are critical for understanding the dynamics of cotton cultivation in arid environments. average solar radiation is 16.3 MJ/m\({}^{2}\). These climatic characteristics of the region are illustrated in Figure 2.  
The two-year experimental trial (2023-2024) was established in a semi-arid agroecosystem historically cultivated with Solanum lycopersicum (tomato) as the preceding crop. Soil taxonomy at the site corresponds to a Topic Torriorthents (USDA classification), with textural analysis confirming sandy loam composition (72% sand, 18% silt, 10% clay). Pre-planting soil characterization involved composite sampling of 30 randomized cores (2.5 cm diameter) from the Ap horizon (0-20 cm depth), homogenized and air-dried to constant mass. Quantitative analysis revealed critical fertility parameters:  
Organic carbon: \(8.55\pm 0.23\) g kg\({}^{-1}\) (Walkley-Black wet oxidation);  
Total phosphorus: \(1.07\pm 0.05\) g kg\({}^{-1}\) (microwave-assisted HNO\({}_{3}\) digestion/ICP-OES);  
Bioavailable phosphorus (Olsen-P): \(10.15\pm 1.2\) mg kg\({}^{-1}\); \begin{table}
\begin{tabular}{l c c} \hline
**Parameter** & **Shallow Layer (10–20 cm)** & **Deep Layer (40–100 cm)** \\ \hline Particle size distribution & & \\  Gravel (\(>\)2 mm, \%) & 7.0 & 8.0 \\  Sand (0.05–2 mm, \%) & 31.0 & 31.0 \\  Slit (0.002–0.05 mm, \%) & 46.0 & 43.0 \\  Clay (\(<\)0.002 mm, \%) & 23.0 & 26.0 \\ _Solid texture class_  
USDA texture classification; [ENDFOOTNOTE]  
\({}^{b}\) Cation exchange capacity. Data represent mean values of triplicate samples collected during pre-planting seasons.  
\end{table} 
Table 2: Physicochemical Characteristics of Soil Profiles in the Experimental Site. Figure 2: The Climate Characteristics Figure for the Experimental Site in 2023 and 2024, encompassing daily solar radiation, daily maximum and minimum temperatures, and daily rainfall. * Total nitrogen: 0.91 \(\pm\) 0.03 g kg\({}^{-1}\) (Kjeldahl digestion);
* Mineral N (NO\({}_{3}^{-}\) + NH\({}_{4}^{+}\)): \(37.8\pm 2.1\) mg kg\({}^{-1}\) (2 M KCl extraction);
* Soil-water pH (1:2.5): 7.50 \(\pm\) 0.15. The experiment involved the artificial planting of Zhongmian 113, a commonly grown cotton variety in the study area. The cotton planting rows were spaced at 10 + 66 + 10 + 66 + 10 cm intervals, with a plant spacing of 10 cm. Precision sowing was carried out using one film, three tubes, and six rows. Chemical fertilizers used in the experiment included urea (46.3% N), ammonium phosphate (12% N, 61% P2O5), and potassium sulfate (51% K2O). Different nitrogen fertilization conditions were applied during the experiment, while irrigation conditions remained constant.