Optimizing irrigation strategies to improve the soil microenvironment and enhance cotton water productivity under deep drip irrigation

Subsurface drip irrigation in arid areas has the potential to replace traditional mulched drip irrigation to achieve green and sustainable cotton production. However, the suitable irrigation amount and frequency are still unclear, which seriously limits the ability of this model to improve water productivity and water-saving potential. Therefore, a field experiment was carried out from 2021 to 2023; a split plot experimental design was adopted with two irrigation amounts (W1, 3177 m³ ha⁻¹; W2, 3840 m³ ha⁻¹) and three irrigation frequencies (F1, 9; F2, 8; F3, 7). The effects of different irrigation strategies on the soil microenvironment, moisture content, biomass, and water use efficiency (WUE) of cotton organs were evaluated. The W2 treatment improved the soil moisture content, increased the soil temperature gradient, and reduced the soil conductivity, thereby increasing the moisture content and biomass of various organs. Moreover, compared with the F1 treatment, the F2 and F3 treatments were more likely to increase the soil moisture content, soil temperature gradient, WUE_Stem, WUE_Leaf and WUE_Boll. In addition, the water consumption of the F2 and F3 treatments decreased by 3.9 % and 0.9 %, respectively, compared with that of the F1 treatment. These findings indicate that W2F2 can reduce water consumption while increasing boll biomass and WUE_Boll. Further analysis revealed that under W2F2, WUE_Boll was positively correlated with soil temperature gradient and soil conductivity and negatively correlated with leaf moisture content (LMC) and water consumption. In summary, with an irrigation amount of 3840 m³ ha⁻¹, delaying the initial irrigation event and increasing the irrigation quota (8 irrigation events) improve the water environment in cotton fields, reducing soil temperature fluctuations and surface salt accumulation and synergistically increasing the boll biomass of cotton organs and WUE_Boll. This irrigation strategy represents an effective cotton cultivation method to maximize cotton yield and improve resource utilization efficiency.