Effects of various soil water potential thresholds for drip irrigation on soil salinity, seed cotton yield and water productivity of cotton in northwest China

As a vital cotton producing region, the arid and semi-arid region of northwest China has faced increasing scarcity of water resources, and the associated decline in irrigation capacity has necessitated the adoption of more efficient irrigation methods in this region. A two-year field experiment was carried out in Northern Xinjiang of China in 2020 and 2021 to explore the effects of various soil water potential (SWP) thresholds (−10, −20, −30 and −40 kPa) for drip irrigation on soil salinity, soil temperature, cotton growth, seed cotton yield, harvest index and water productivity. The results showed that with the decrease of SWP threshold, soil moisture in the 0–20 cm soil layer decreased gradually, while soil salinity decreased first and then increased. Soil salt content was lowest under − 20 kPa, and soil salinity was controlled below the root zone. SWP thresholds of −10 and −20 kPa could well control soil temperature during the whole growing season of cotton to reduce heat stress. Higher SMP was beneficial to plant height, leaf area and stem diameter, but it did not significantly improve seed cotton yield. The effects of soil moisture, heat and salt on growth indexes and seed cotton yield were quantitatively evaluated based on the path analysis. The number of cotton boll was the most influential growth variable on seed cotton yield, and soil salt content had the most significant influence on boll number. High-frequency irrigation (−10 kPa) was not conducive to reducing soil salinity, increasing boll number and increasing seed cotton yield. Drip irrigation with SWP threshold of −20 kPa was recommended for drip-irrigated cotton under film mulch in Northern Xinjiang. This study can provide scientific basis for irrigation management of cotton in saline-alkali regions.