Yield and water productivity of crops, vegetables and fruits under subsurface drip irrigation: A global meta-analysis

The rapid population growth and economic development, climate change and irregular rainfall will inevitably intensify the competition of water resources, resulting in the reduction of agricultural irrigation water. In recent years, subsurface drip irrigation (SSDI), as an efficient water-saving irrigation technology, has been widely used in crop production, but its effects on crop yield, irrigation water productivity (IWP) and water productivity (WP) vary with field managements, climatic conditions and soil properties. Here, a global meta-analysis of 984 comparisons from 109 publications was carried out to systematically and quantitatively analyze the responses of yield, IWP and WP of crops, vegetables and fruits to SSDI. The results showed that SSDI significantly increased yield, IWP and WP by 5.39%, 6.75% and 3.97% relative to surface drip irrigation (SDI), respectively. The largest percentage increase in yield was observed in crops (6.42%), followed by vegetables (5.29%) and fruits (3.37%). SSDI performed best when crops, vegetables and fruits were planted in the open field, under film mulching, in arid regions (< 200 mm) and in regions with mean annual temperature > 12 celcius. Besides, the emitter spacing < 25 cm, emitter discharge rate of 2.5-3.5 L h(-1) and buried depth of drip pipe < 10 cm were beneficial to obtaining higher increases of yield, IWP and WP. In addition, yield was significantly affected by fertilization rate, and the maximum percentage increase in yield was obtained with 100-200 kg N ha(-1), < 50 kg P ha(-1) and < 100 kg K ha(-1). Yield, IWP and WP were also significantly affected by soil factors. The percentage changes in yield and IWP in soils with higher bulk density (> 1.4 g cm(-3)) and in acid soils (pH < 7) were significantly higher than those in soils with lower bulk density (< 1.4 g cm-(3)) and in neural and alkaline soils (pH > 7). In conclusion, SSDI can improve yield and WP, but the application of SSDI should be site-specific.