Crop yield and water productivity under salty water irrigation: A global meta-analysis

Due to the declining availability of freshwater resources to agricultural systems especially in arid and semi-arid regions, marginal quality water resources (e.g., brackish or saline water) are getting more attention for irrigation. For optimal management and long-term productivity, the knowledge on responses of crop yield, water productivity (WP) and irrigation water productivity (IWP) to salty water irrigation under different crop types, soil properties, irrigation management practices and climate environments is needed. Here, a global meta-analysis of 1151 comparisons from 120 publications was adopted to systematically analyze the responses of crop yield, WP and IWP to salty water irrigation. Overall, salty water irrigation significantly decreased crop yield (−17.3%), WP (−12.4%) and IWP (−10.8%) compared to fresh water irrigation. Compared with brackish water irrigation (irrigation water electrical conductivity (ECi) ≤ 3.0 dS m−1), saline water irrigation (ECi: 3.0–15.7 dS m−1) caused larger reductions of crop yield, WP and IWP. Cotton performed best under saline water irrigation (ECi: 3.0–15.7 dS m−1), followed by wheat, maize, tomato and pepper. Brackish water irrigation (ECi ≤ 3.0 dS m−1) did not cause significant differences in the percentage decreases of crop yield and WP among the five crops. Brackish water irrigation performed best in the medium soil, and the percentage changes of crop yield, WP and IWP were −10.1%, −13.2% and 23.5%, respectively. Decreased soil bulk density and increased soil pH significantly increased crop yield regardless of irrigation water salinity. Farmers in semi-humid regions (MAP: 400–800 mm) and applying drip irrigation were more possible to obtain higher crop yield under salty water irrigation. The percentage changes of WP and IWP of salty water irrigation were smaller under drip irrigation than those under furrow irrigation. These results can help to optimize salty water irrigation management practices.