Meta-analysis of water-saving and yield-increasing effects of different drip irrigation methods in Northern China

This study was to assess the water-saving and yield-increasing differences between subsurface drip irrigation (SSDI) and surface drip irrigation (SDI) under various regional, crops, climatic, soil, field management, and drip irrigation technical factors. The data for this study were collected from literature published before November 4, 2023. The selection criteria included: 1) experiments conducted in fields in northern China; 2) data collection limited to field experiments only; 3) experiments involving both subsurface drip irrigation and surface drip irrigation treatments, with all other field trial conditions strictly consistent; 4) the article must provide at least paired data on yield, water use efficiency, or economic benefits (net benefits), as well as sample size and standard deviation. A total of 223 sets of yield data, 148 sets of water use efficiency data, and 31 sets of economic benefit (net benefit) data were obtained. The results showed that compared to SDI, SSDI could increase crop yield by 6.66% overall, improve water use efficiency by 9.34% and increase net benefits by 6.94%. When the average annual temperature was ≥12 ℃and <12 ℃, SSDI could significantly increase crop yield by 11.05% and 5.69%, respectively, and significantly improve water use efficiency by 8.18% and 5.24%, respectively, but the inter-group differences were not significant. Compared to SDI, when the annual precipitation was ≤200 mm and 200-400 mm, SSDI could significantly increase crop yield by 7.11% and 6.39%, respectively, and significantly improve water use efficiency by 7.29% and 3.89%, respectively. Compared to SDI, SSDI could significantly increase crop yield by 7.02% and 5.04% in the northwest and north China regions, respectively, and significantly improve water use efficiency by 8.57% and 10.46%, respectively, while the water-saving and yield-increasing effects were not significant in the northeast region. Compared to SDI, SSDI could significantly increase the yield of vegetables, and food crops by 9.7% and 5.14%, respectively, and significantly improve water use efficiency by 14.04% and 4.9%, respectively, but the water-saving effect on fruit crops was not significant. Compared to SDI, when the soil bulk density was ≥1.5 g/cm³ and <1.5 g/cm³, SSDI could significantly increase crop yield by 6.82% and 3.12%, respectively, and significantly improve water use efficiency by 9.44% and 3.48%, respectively. Compared to SDI, SSDI performed better under clay and sand soil conditions, significantly increasing crop yield by 10.92% and 8.31%, respectively, and significantly improving water use efficiency by 8.95% and 5.25%. Compared to SDI, SSDI with and without mulching could significantly increase crop yield by 7.21% and 5.18%, respectively, and significantly improve water use efficiency by 5.77% and 8.72%, respectively, but the difference between the two mulching measures was not significant. The higher the irrigation and fertilization frequency, the better the water-saving and yield-increasing effect of SSDI compared to SDI. When the depth of buried pipes was >15-25 cm, and the emitter discharge of drip pipe was between >1.5-<2.5 L/h, it was more conducive to realizing the advantages of SSDI, and the water-saving and yield-increasing effect was significant. In northern China, subsurface drip irrigation has a significant water-saving and yield-increasing effect compared to surface drip irrigation, especially in arid and low rainfall climate conditions. This study provided a theoretical basis for the promotion and application of subsurface drip irrigation in northern China.