Soil water and salt distribution and their controlling factors under mulched drip irrigation: A meta-analysis

Mulched drip irrigation (MDI) improves water use efficiency in arid regions, but also leads to heterogeneous soil water and salt distribution. Based on a meta-analysis of 385 soil profiles from 87 publications, we investigated this distribution and its influencing factors. Results showed that soil water heterogeneity in the 0–40 cm layer is negatively correlated with field capacity, positively correlated with sand content, emitter flow and days after irrigation, and affected by climate and crop type. MDI led to salt redistribution rather than leaching, resulting in desalination in the root zone and salt accumulation in bare areas and deeper layers. Specifically, salt accumulation in bare areas was 1.9 times that in root zones, and accumulation in the 40–60 cm layer under the mulch was 1.38 times. This accumulation correlates positively with initial soil salinity and irrigation amount, and negatively with emitter flow. The depth of salt accumulation under the root zone is not strongly influenced by irrigation (saline water irrigation, irrigation amount) or environmental factors (crop type, groundwater level, initial salinity), but is jointly regulated by emitter flow and soil sand content. When sand content is < 50 %, accumulation becomes shallower with higher flow, concentrating at 20–40 cm; at > 50 % sand content, accumulation depth increases with flow. Saline water irrigation resulted in a more uniform salt profile than freshwater but increased overall salinity in the 0–80 cm layer. These findings provide critical insights for optimizing MDI strategies to achieve sustainable agriculture in arid regions.