Deficit irrigation alleviates the increase in soil salinity content in saline-alkali regions of China and improves irrigation water productivity: A meta-analysis

Saline-alkali land, an important reserve of arable land resource, is key to ensuring food security and sustainable agricultural development. Deficit irrigation (DEI) presents a feasible solution to alleviate water scarcity and develop saline-alkali land. However, the effects of DEI on soil salinity content, crop yield, and irrigation water productivity (IWP) in saline-alkali regions remain unclear. This study conducted a meta-analysis of 1108 comparisons from 39 studies on DEI in saline-alkali regions of China. In addition, machine learning was used to assess the effects of agronomic practices and environmental factors on soil salinity content, crop yield, and IWP, and to explore suitable DEI strategies for crop cultivation in these regions. It was found that, although DEI increased soil salinity content by 2.52 % and decreased crop yield by 6.77 % compared with full irrigation (FUI), it increased IWP significantly by 29.77 %. Overall, the results varied, depending on irrigation practices (such as irrigation proportion, salinity of irrigation water and irrigation method), climatic conditions (such as precipitation, temperature and evaporation), soil conditions (soil properties, groundwater depth and initial soil salinity) and crop types (four major crops: maize, wheat, cotton and oil sunflower). In order to maximize the trade-off effects, we found that DEI is most appropriate for regions where annual precipitation exceeds 200 mm and soil bulk density of 1.45–1.55 g/cm 3 . Compared with flood irrigation or drip irrigation alone, the combination of the two is more likely to achieve controlled salinity, stable production, and high IWP. Random forest model analysis suggested that salinity of irrigation water was more critical for soil salinity content and IWP. DEI using slightly brackish water (0.7–2 dS/m) and an irrigation proportion of 0.85–0.9 crop evapotranspiration (ET c ) is more likely to achieve a trade-off between soil salinity content, crop yield, and IWP. This study provided valuable insights into the response of crop cultivation to DEI in saline-alkali regions of China and offered scientific recommendations for its application. • Deficit irrigation reduced the increase in soil salinity content in saline-alkali planting regions to 2.52 %. • Deficit irrigation performed best when salinity of irrigation water was 0.7–2 dS/m and irrigation proportion was 0.85–0.9 ET c . • Trade-off effects were largest when mean annual precipitation > 200 mm and soil bulk density was 1.45–1.55 g/cm 3 . • The integration of drip and flood irrigation was the optimal strategy for soil salinity control in saline-alkali regions.