tructural deviations are inevitably observed in the key components after mass production, such as mold manufacturing and injection molding. The internal flow field can be different than before in the labyrinth-channel drippers. It is often required to balance hydraulic stability and overall production costs. In this study, the precision grading control scheme was established to guide better hydraulic performance of the drippers. A systematic investigation was made to quantify the sensitivity of the hydraulic performance of labyrinth path irrigation emitters to manufacturing deviations of the key geometric parameters. Furthermore, the simulation and experiment were conducted to validate the numerical model using Computational Fluid Dynamics technology. Single-factor optimizations were then conducted on five structural parameters of the labyrinth path: path depth, tooth height, tooth bottom distance, tooth angle, and tooth tip fillet radius. Each geometric parameter was independently evaluated to accurately reflect manufacturing deviations at seven levels. Local sensitivity evaluation was integrated with a microscopic examination of the flow field, specifically tracking the evolution patterns of vortex structures, velocity distributions, and turbulent kinetic energy. The results demonstrated that the manufacturing deviations significantly altered the internal flow dynamics and overall hydraulic characteristics. Microscopic flow field analysis revealed that tooth height and tooth tip fillet radius were the key parameters to regulate vortex structures and energy dissipation. Specifically, a negative deviation of 0.05 mm in tooth height expanded the near-wall vortex zones, resulting in an 8.91% variation in the vortex area ratio, whereas the impact of the tooth angle was negligible at less than 1%. Furthermore, the deviations in tooth height, tooth bottom distance, and fillet radius notably modified the velocity distribution and local throttling. For example, the tooth height was reduced by 0.05 mm, while the average velocity decreased by 4.03%, but the high-speed area expanded by 21.94 %, due to enhanced separation and turbulence. Similarly, the fillet radius was reduced by 0.03 mm in the mainstream area, thus decreasing the average velocity by 4.68 %. In energy dissipation, the maximum deviations in tooth height and fillet radius were reduced by the average turbulent kinetic energy by 9.16%and 7.85%, respectively. Interestingly, the decreasing tooth height and bottom distance drastically expanded the high turbulent kinetic energy areas by 378.75% and 467.28%, respectively, directly indicating flow uniformity. The sensitivity analysis indicated that the flow coefficient was most sensitive to path depth, with a coefficient of 1.17, followed by tooth bottom distance at 0.66. Conversely, the flow regime index was most sensitive to tooth height. Overall, the sensitivity of the flow rate to the geometric parameters was ranked from highest to lowest: path depth, tooth height, tooth bottom distance, tooth tip fillet radius, and tooth angle. According to the sensitivity ranking and internal flow characteristics, a precision grading control strategy was proposed to maintain the target flow rate variation within ±5%. Extremely sensitive path depth required strict tolerance control within ±0.02 mm. Tooth height was recommended to be controlled within ±0.03 mm to prevent the severe deterioration of turbulent kinetic energy. The recommended tolerances for tooth bottom distance and fillet radius were ±0.07 mm and ±0.01 mm, respectively. In view of the minimal impact on the flow field, the tolerance of the tooth angle is required to consider anti-clogging and structural assembly.

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.