Adopting different cotton cropping systems may regulate the spatiotemporal variation in soil moisture and affect the growth, WUE and yield of cotton

Approximately 70% of global cotton production is under the threat of drought. Changing cropping systems is an agronomic measure that potentially coordinates production and ecology. However, little evidence is available on the characteristics of changes in the soil moisture under different cropping systems and their relationships with cotton production. This study assessed the temporal and spatial variation in the soil moisture and analyzed the relationships between the soil water content (SWC) and the biomass, yield, and water use efficiency (WUE) of cotton (Gossypium hirsutum L.) in three cropping systems (monoculture cotton (MC), wheat (Triticum aestivum L.)/delayed intercropped cotton (WIC), and wheat/direct-seeded cotton (WDC)). The spatiotemporal heterogeneity and autocorrelation of the soil moisture were affected by cropping systems and whether the soil was dry or wet. Compared with the values in 2016 (moist), the spatiotemporal heterogeneity in the SWC variation at a 10–110 cm depth in the three planting systems increased, and the autocorrelation decreased in 2017 (drought). This phenomenon was more pronounced in WIC than in MC and WDC. Compared with MC, the double-cropping system increased the SWC between cotton rows. In the double-cropping system, the cotton yield of WIC was significantly higher than that of WDC. The order of WUE from high to low was WDC>MC>WIC in 2016 and MC>WIC>WDC in 2017, and no significant difference was observed between MC and WIC in both years. Yield limitation in the double-cropping system was due to weak water absorption of roots. The growth curves of cotton roots with increasing SWC in WIC were similar to those in MC, while WDC showed faster root growth but a smaller maximum value. The roots in WDC stopped growing when the water consumption reached 150 mm. WDC with a small root system was suitable for humid regions, while WIC with a strong root system should be promoted in both humid and arid regions. The methods and results can be used to obtain a deeper understanding of the effects of different planting systems on soil moisture and cotton production and to determine their interrelationship to guide dryland cotton production and precision agriculture.