Effects of Reduced Winter Irrigation Frequency on Soil Properties, Microbial Communities, and Cotton Establishment in Southern Xinjiang

Water scarcity increasingly restricts conventional annual winter irrigation in cotton production systems of southern Xinjiang, yet the consequences of reducing winter irrigation frequency for soil properties, microbial communities, and crop establishment remain unclear. A long-term field experiment was conducted in a drip-irrigated cotton field to compare annual winter irrigation (CK), continuous omission of winter irrigation (H1), winter irrigation with one intervening non-irrigated winter (H2; once every two years), and winter irrigation with two consecutive intervening non-irrigated winters (H3; once every three years). Soil water and salinity, nutrient contents, enzyme activities, microbial biomass and community characteristics, cotton emergence, and seed cotton yield were evaluated. Complete omission of winter irrigation resulted in the greatest salt accumulation and reduced soil moisture, whereas H2 and H3 maintained higher soil organic matter and total nutrient contents than CK. H3 also showed higher microbial biomass carbon and the greatest bacterial and fungal richness. RDA indicated that soil salinity, total potassium, microbial biomass carbon and nitrogen, and enzyme activities were significantly associated with microbial community composition. Winter irrigation frequency significantly affected cotton emergence but not seed cotton yield; H3 produced the highest emergence rate without a significant yield penalty. Overall, periodic winter irrigation, particularly the H3 regime, showed potential to reduce long-term winter irrigation frequency while maintaining favorable soil properties and cotton establishment. Multi-year measurements of yield and irrigation water use are required before this regime can be recommended for long-term management.