Effects of irrigation amounts on spatiotemporal dynamics of root-zone soil moisture-temperature-salinity-nutrients and water productivity in grey jujube orchards under subsurface drip irrigation

Low water use efficiency and soil salinization have long plagued the sustainable development of agriculture in arid and semi-arid regions. As a distinctive water-saving irrigation technology, subsurface drip irrigation (SDI) can reduce surface evaporation and ameliorate the root-zone soil environment of crops. To clarify the effects of irrigation management on the spatiotemporal dynamics of the root-zone environment in grey jujube orchards and its regulatory mechanism on yield and water productivity (WP) under SDI in southern Xinjiang, China, a two-year field experiment was conducted using grey jujube trees with SDI, with four irrigation amounts: 360 mm, 480 mm, 600 mm, and 720 mm (designated as W1, W2, W3, and W4, respectively). The results showed that soil moisture exhibited a unimodal distribution pattern of “low in the surface layer, high in the middle layer, and stable in the deep layer” during the irrigation cycle, while soil salinity presented a valley-shaped distribution of “salt accumulation in the surface layer, desalination in the middle layer, and salt accumulation in the deep layer”. Increasing irrigation amounts led to a significant decrease in soil temperature, and this regulatory effect was more prominent in the inter-row area, during the fruit expansion stage, and at the diurnal peak period. Both nitrate nitrogen (NO 3 - -N) and available potassium (AK) formed an ellipsoidal high-value area centered directly below the dripper, while available phosphorus (AP) accumulated at the soil surface. The highest fruit yield was obtained under W3, reaching 15429.90 kg ha −1 and 17706.60 kg ha −1 in the two growing seasons, respectively. WP peaked under the W1 treatment, which was 8.75% - 27.94% and 11.58% - 50.00% higher than the other irrigation treatments in the two years, respectively. Correlation analysis and partial least squares-structural equation modeling (PLS-SEM) further revealed that SDI promoted jujube trees' growth and increased fruit yield and WP by improving the soil water, temperature, salinity, and nutrients conditions in the root zone. Comprehensively considering the soil environment, jujube growth, yield, and WP, W3 is recommended as the suitable irrigation amount for the study area. This study provides theoretical support for the sustainable production of grey jujube with SDI in southern Xinjiang, China.