In order to clarify the influences of drip irrigation under different mulch materials on crop yield, field experiments were carried out in the North China Plain for two seasons in 2020 and 2021. The changes in field microenvironment, photosynthetic capacity, leaf biological factors, and maize growth indexes were analyzed under drip irrigation with transparent film (W), black film (B), and straw mulching (S), with a nonmulching field as control (CK). The results showed that compared with CK, the yield of W and B increased by 7.2–9.9% and 7.1–12.4%, and the yield of S did not change significantly. The increase in yield was related to the improvement of the field microenvironment and photosynthetic capacity and higher LAI. Compared with CK, the soil water content 0–40 cm below the soil surface of W, B, and S increased by 13.6%, 9.1%, and 4.6%, respectively, and the 5 cm effective accumulated soil temperature of W and B increased by 7.9–10.2% and 4.1–4.7%, respectively. The maximum carboxylation rate (V_max) of W, B, and S at the jointing stage was significantly increased by 3.5–17.3%, 12.7–17.6%, and 10.1–12.7% compared with CK. There was a significant linear correlation between V_max and N_mass, and the correlation was affected by mulching treatments. At the jointing stage, compared with the CK, the LAI of W and B significantly increased by 8.6–66.5% and 7.2–56.0%, but there was no significant difference between S and CK. In conclusion, the increase in yield of W and B resulted from the combined effect of increasing LAI, V_max, and soil water content and temperature.

We created a subsurface drip irrigation (SDI)-specific variable flow emitter (VFE) that switches working stages automatically based on the inlet pressure (H) to achieve a step change in the flow rate. At working stage I (H = 0.1 MPa), namely the conventional water supply stage, the VFE provided a normal flow rate (q_I) of 1–2 L/h for crop irrigation. At working stage II (H > 0.1 MPa; exceeding the design pressure), VFE delivered a larger flow rate (q_II). The larger q_II facilitated water movement upward from the underground to the surface seedbed during the crop planting, thus ameliorating crop germination issues under SDI. We focused on the impacts of four structural parameters of the flow channel: tooth height (E), tooth spacing (B), tooth angle (A), and flow channel depth (D) on the q_I and VFE-flow index (x) at working stage I. Computational fluid dynamic (CFD) simulations were conducted along with a physical laboratory test to develop VFE using computerized numerical control (CNC) technology (accuracy = 0.05 mm). Nine VFEs were designed using an L9(3⁴) orthogonal test. The combination of tetrahedral meshing with a six-layer boundary layer and the realizable k–ε turbulence model was found suitable for CFD simulations. The standard root-mean-square error (nRMSE) of the measured and simulated q_Is was a minimum of 7.4%. The four parameters influenced q_Is as D > B > E > A, and the four factors influenced the x_s as B > E > D > A. Based on the numerical simulation data, multiple linear regression models were constructed for the q_Is and x_s with four parameters when H = 0.1 MPa. Aiming for the minimum x, the optimal combination of the flow channel structural parameters corresponding to different q_Is was determined by the ergodic optimization algorithm. When q_I was 1.5 L/h, the optimal structural combinations were E = 1.2 mm, B = 1.8 mm, A = 42°, and D = 1 mm. The VFE with a q_I of 1.5 L/h was created by CNC technology. The relative errors of the measured and predicted q_Is using the regression model were −0.19–6.31%, and their nRMSE was 6.76%. Thus, optimizing the flow channel structural parameters based on a multiple linear regression model and the ergodic optimization algorithm is a highly precise theoretical base for VFE development.

Reducing the flow rate (q) of the emitter can increase the dripline laying length and reduce the engineering investment of the drip irrigation system; however, reducing q increases the risk of emitter clogging. In this study, based on the OPFN method (Optimal Latin Hypercube Experimental Design–Parametric Modeling of Emitter–Fluid Dynamics Simulation–NSGA-II Genetic Algorithm Optimization), we selected the structural parameters of channel tooth height (E), angle (A), pitch of teeth (B), and flow channel depth (D) to construct 128 emitters. Through simulation, we obtained q, the flow index (x), and the structural resistance coefficient (Cs) under the pressure (H) ranging from 0.02 to 0.15 MPa. The results showed that the rated flow rate (q_0.1) and x values of 128 emitters range from 0.50 to 0.85 L/h and 0.461 to 0.480, respectively. Since Cs is negatively correlated with x, to obtain the combination of the flow channel structural parameters with the optimal hydraulic performance (x = min f(E, A, B, D)) and the optimal anti-clogging performance (Cs = min g(E, A, B, D)), the flow channel structural parameters are optimized by using the NSGA-II genetic algorithm to obtain the Pareto frontier solution. The optimal combinations of channel structural parameters corresponding to the q_0.1 values of 0.62, 0.71, and 0.82 L/h with x of 0.470, 0.466, and 0.463 are obtained using the weighting method. Cs values are 0.131, 0.446, and 0.619, respectively. The limit laying length of the configured emitter is 150–180 m. According to the flow field cloud diagram before and after optimization, it can be found that increasing the high-velocity area and high-turbulent-kinetic-energy area in the main stream and decreasing the low-velocity area and low-turbulent-kinetic-energy area in the tooth base and downstream face can help reduce x and Cs, and thus improve the hydraulic performance and anti-clogging performance of the small flow rate emitter.

Variable flow emitters are used in subsurface drip irrigation to address challenges in soil moisture transport. This study investigates the impact of flow channel structural parameters on the hydraulic performance and anticlogging ability of emitters using computational fluid dynamics (CFD) simulations and experimental tests. The results show that the realizable k–ε turbulence model can be used to simulate the flow field inside the variable flow emitter flow channel. The nRMSE between the measured (q_m) and simulated (q) values of the flow rate is 11.23%, and the relative error between the measured (x_m) and simulated (x) values of the flow index is 4.66%, which gives a high simulation accuracy. A polar analysis shows that the tooth angle (A) has the smallest effect on the effluent flow rate at 0.1 MPa (q_0.1), x, and particle passage rate (η) of the variable flow emitter. Flow channel depth (D), tooth spacing (B), and tooth height (E) have a different order of precedence in the influence of the three indices, which are D > B > E > A, B > E > D > A and E > B > D > A, respectively. The value of η is positively correlated with the mean flow velocity (v) and the mean turbulent kinetic energy (k) in the flow channel, and η tends to increase and then decrease with the increase of x. The retention time of the particles in the flow channel is closely related to the magnitude of v and k. Three multivariate lin ear regression equations (R² = 0.883–0.995) were constructed for q_0.1, x, and η versus the flow channel structural parameters. The optimal design combination of channel structure parameters for different scenarios was determined using the scipy.optimize.minimize function in Python 3.8.0. The research results provide a reference for the optimal design of variable flow emitters.

Canopy conductance (G_c) is an important biological constant for quantifying the water vapor flux at the canopy-atmosphere interface, reflecting the coupling strength between crop transpiration and microclimate. To elucidate how mulching modulates G_c dynamics under varying environments, we measured the transpiration of maize based on thermal equilibrium method from 2020 and 2021, synchronously recording solar radiation (R_s), temperature (T), relative humidity (RH), and vapor pressure deficit (VPD) under no-mulching (NM), transparent film (TFM), black film (BM), and straw mulching (SM) treatments in the North China Plain. The results showed that in the near-surface microenvironment, at early stages (seedling-jointing), compared to the NM treatment, TFM and BM treatments unexpectedly reduced temperature by 0.1–1.1% while increasing humidity by 0.2–4.0%, lowering VPD by 0.7–15.5%, contradicting presumed warming effects. During tasseling-filling stages, both plastic films elevated temperature by 3.5–5.2%, decreased humidity by 5.2–6.9%, and sharply increased VPD by 23.4–27.6%, inducing heat-VPD coupling stress. Throughout the entire growth period, SM treatment resulted in an initial increase followed by a decrease in temperature, but the decrease in humidity and increase in VPD occurred earlier and smoothly compared to film mulching treatment in the near-surface microenvironment. All treatments increased average temperature but decreased average humidity in the near-ground microenvironment throughout growth stages, ultimately leading to an increase in average VPD. In addition, all treatments increased G_c at noon by 10.3–81.2%. Under different solar radiation conditions, TFM, BM, and SM treatments increased the reference conductance (G_cR) but did not always increase G_c sensitivity to VPD (m). We propose a specific mulching strategy: Using black or transparent plastic film mulching in arid/cold regions and straw mulching in high-temperature and drought-prone/rain-fed agricultural areas can reconcile the trade-off between microclimate optimization and physiological adaptation, advancing precision water management in arid-prone croplands.