Soil water, salt, and nutrient variability are essential factors that impact crop productivity in agriculture systems. However, effective management of small farms requires access to fine-scale data on soil water, salt, and nutrients. Large-scale assessments of spatial variability using classical statistics and geostatistical methods can help identify nutrient-deficient zones. In Xinjiang, China, inadequate water and nutrient management has resulted in low crop productivity in agriculture systems. To address this issue, this study evaluated the mechanical composition, bulk density, and contents of water, salt, ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3--N), and available phosphorus (A-P) in soil at the farm level in the Xinjiang region. Results showed low variability in soil bulk density, medium variability in soil water content, mechanical composition, NO3--N, and A-P, and high variability in soil salt content and NH4+-N. Mechanical composition and A-P showed a small range of variation across different soil depths, while soil water content and NO3--N in the surface layer varied significantly more than in other soil layers. NH4+-N variability increased with soil depth. Soil properties showed minimal differences over time. Multi-factor deficiencies, particularly in nitrogen, were observed throughout the study area. The generated maps offer a useful tool for farm managers and policymakers. In summary, this study highlights the significance of evaluating the spatial variability of soil properties for identifying zones deficient in water and nutrients, as well as those with salt accumulation. This information can be utilized to develop effective strategies for site-specific nutrient management.

In irrigated agriculture, the combination of multiple regulation measures is an effective method to improve saline soil and promote crop growth. Magnetized ionized water irrigation is considered a promising irrigation water activation technique, while the use of Bacillus subtilis for soil amelioration is environmentally friendly. In this study, magnetized ionized water irrigation and B. subtilis were used to promote cotton growth under film-mulched drip irrigation (FMDI) in saline soil. A two-year field experiment was conducted to investigate the effects of differing B. subtilis amounts under two irrigation water types (non-magnetized-ionized water (NMIW) and magnetized ionized water (MIW)) on the growth (plant height, leaf area index, shoot dry matter and chlorophyll content) and the yield of cotton, as well as the soil water content, salts accumulation, water use efficiency (WUE) and irrigation water use efficiency (IWUE) under FMDI in a saline soil in southern Xinjiang. Five amounts of B. subtilis (0, 15, 30, 45 and 60 kg ha−1) under NMIW (designated as B0, B1, B2, B3 and B4) and MIW (designated as M, MB1, MB2, MB3 and MB4) were applied to the field experiments. The results showed that MIW and B. subtilis increased soil water content and reduced salts accumulation in the 0–40 cm soil layers compared with B0. Moreover, the two measures significantly (p < 0.01) increased cotton plant height, leaf area index, shoot dry matter and chlorophyll content compared with B0. Seed cotton yield, WUE and IWUE were also observed to significantly increase (p < 0.05). Compared with the NMIW treatments, the MIW treatments increased seed cotton yield by 2.1–12.2%, increased WUE by 0.2–9.0%, and increased IWUE by 2.1–12.2%. Under MIW, with the B. subtilis amount as an independent variable, quadratic function relationships with seed cotton yield, WUE and IWUE were established. By taking the first derivative of the quadratic function, the highest seed cotton yield, WUE and IWUE were obtained with the B. subtilis amounts of 51.8, 55.0 and 51.4 kg ha−1, respectively. Based on comprehensive consideration of seed cotton yield, WUE, IWUE and salts accumulation in soil, 51.4 kg ha−1 of B. subtilis under MIW treatment is recommended for cotton cultivated under FMDI in a saline soil of southern Xinjiang, China.