Meta-Analysis of the Effect of Subsurface Irrigation on Crop Yield and Water Productivity

Problems such as population growth and climate change have led to a reduction in the use of water for irrigated agriculture, constraining the growth of crops. Subsurface irrigation, as a widely used and efficient water-saving irrigation technology, varies in its effect on increasing yields and saving water under different environmental, management, and other conditions. To investigate the effects of subsurface irrigation on yield, water productivity (WP), and irrigation water productivity (IWP) of three typical crops (wheat, maize, and cotton), this paper conducted a meta-analysis of 528 pairs of studies from 64 papers worldwide to quantify the response of crop yield, WP, and IWP to subsurface irrigation. Overall, the yield, WP and IWP increased by 5.96%, 21.62%, and 27.72%, respectively, with subsurface irrigation compared with surface irrigation. Compared with other conditions, the greatest rate of change was observed at around 200–500 m above sea level, 10–15 °C average annual temperature, 1.45–1.55 g/cm3 soil bulk density, alkaline soil, and when the crops were planted with equal row spacing. Meanwhile, the amount of irrigation water, as well as the subsurface pipeline arrangement and burial depth, had significant effects on crop yield, WP, and IWP. The maximum increase in crop yield, WP, and IWP was favored when the irrigation volume of the subsurface irrigation was reduced by 50–100% compared with surface irrigation or when both had the same volume of irrigation but a mild water deficit. In addition, the yield, WP, and IWP were also affected by fertilization factors. The recommended fertilizer application rates were ≤90 kg P ha–1 (phosphorus) and –1 (nitrogen). Compared with surface irrigation, subsurface irrigation showed the greatest yield increase when fertilizer was applied in a one-time application, and the WP and IWP increased significantly when the number of fertilizer applications was