For improving water scarcity and groundwater pollution from agriculture, two-year experiments (2011–2013) with three water levels (0.3, 0.5 and 0.8 evaporation (E) in 20-cm-diameter pans) and four nitrogen (N) levels (120, 140 and 190 kg·ha⁻¹ in 2012 and 120, 190 and 290 kg·ha⁻¹ in 2013) were conducted to study effects of water and N availability on water movement and N transport for a wheat crop under drip irrigation in the North China Plain. The results indicated that under drip irrigation, deep percolation at 1-m depth was stable at 0.5–0.8 E with the same N rate for winter wheat. At 0.5–0.8 E, deep percolation was also relatively stable with increasing N rate from 120 to 140 kg·ha⁻¹ or from 190 to 290 kg·ha⁻¹. The irrigation schedule and N rates only affected N leaching below the root zone of winter wheat (60-cm depth), while the N residual in the soil layer presented more risk to the environment than N leaching. In general, the 290-kg-ha⁻¹ N level was not recommended using drip fertigation for winter wheat in the North China Plain. The empirical equation given by the Ministry of Geology and Mineral Resources was also not recommended for estimating the drainage under drip irrigation.

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.

Mulches combined with drip irrigation techniques have been widely applied in China for higher yield and water use efficiency (WUE). To develop an efficient strategy that can improve maize yield and save water in the North China Plain (NCP), we conducted a two-year field experiment, using transparent plastic film mulching (T), black plastic film mulching (B), and straw mulching (S) and non-mulching (N) for spring maize in 2019 and summer maize in 2020, and high drip irrigation amount (H) and low drip irrigation amount (L) were also considered in 2019. We mainly studied the effects of mulches on soil water content, soil temperature, crop growth rate, grain yield, and water use efficiency (WUE). The results indicated that T and B treatment increased soil water content (SWC) and topsoil temperature. The T treatment promoted the growth rate significantly more than N treatment, by 27.7–43.4% at the early stage in two years. The grain yield under TH treatment was significantly (p < 0.05) higher than that of other treatments, by 9.8–17.4% for spring maize in 2019, and significantly (p < 0.05) higher under both TH and BH than under NH, by 8.9% and 4.7% for summer maize in 2020. There was a significant quadratic parabola relationship between ET and grain yield in 2019, and the correlation between SEAT of 0–10 cm soil depth with grain yield or with biomass was positive. These results indicate that the transparent plastic film with high drip irrigation amount treatment (TH) can be recommended for spring maize, and both transparent and black film mulch treatments (TH and BH) can be recommended for summer maize in the NCP.

The development of water-saving management relies on understanding the physiological response of crops to soil drought. The coordinated regulation of hydraulics and stomatal conductance in plant water relations has steadily received attention. However, research focusing on grain crops, such as winter wheat, remains limited. In this study, three soil water supply treatments, including high (H), moderate (M), and low (L) soil water contents, were conducted with potted winter wheat. Leaf water potential (Ψ_leaf), leaf hydraulic conductance (K_leaf), and stomatal conductance (g_s), as well as leaf biochemical parameters and stomatal traits were measured. Results showed that, compared to H, predawn leaf water potential (Ψ_PD) significantly reduced by 48.10% and 47.91%, midday leaf water potential (Ψ_MD) reduced by 40.71% and 43.20%, K_leaf reduced by 64.80% and 65.61%, and g_s reduced by 21.20% and 43.41%, respectively, under M and L conditions. Although g_s showed a significant difference between M and L, Ψ_leaf and K_leaf did not show significant differences between these treatments. The maximum carboxylation rate (V_cmax) and maximum electron transfer rate (J_max) under L significantly decreased by 23.11% and 28.10%, stomatal density (SD) and stomatal pore area index (SPI) under L on the abaxial side increased by 59.80% and 52.30%, respectively, compared to H. The leaf water potential at 50% hydraulic conduction loss (P₅₀) under L was not significantly reduced. The g_s was positively correlated with Ψ_MD and K_leaf, but it was negatively correlated with abscisic acid (ABA) and SD. A threshold relationship between g_s and K_leaf was observed, with rapid and linear reduction in g_s occurring only when K_leaf fell below 8.70 mmol m⁻² s⁻¹ MPa⁻¹. Our findings demonstrate that wheat leaves adapt stomatal regulation strategies from anisohydric to isohydric in response to reduced soil water content. These results enrich the theory of trade-offs between the carbon assimilation and hydraulic safety in crops and also provide a theoretical basis for water management practices based on stomatal regulation strategies under varying soil water conditions.

Soil salinization is a global problem that causes huge losses in agricultural production. Salt can interfere with crop absorption and metabolism of nutrients and water, affect plant physiological responses and reduce plant biomass. Maize, a very important economic crop, can adapt to a certain degree of saline-alkali soil. It is essential to understand the physiological indexes of response to soil salinity concentrations and explore the effects of different nitrogen fertilizer treatments on maize growth. In this study, three soil salinity gradients (S1, S2 and S3 were with soil salt concentration, Ssc, of 0, 0.1% and 0.25%, respectively) and two nitrogen application rates (N0 and N1 were without and with nitrogen applied (13.2 g per pot), respectively) were set up. Plant growth and photosynthetic parameters were measured. Whether nitrogen was applied or not, with the increase in Ssc, leaf area, plant height, stem diameter, SPAD, leaf water potential, RuBP carboxylase, and PEP carboxylase activities, photosynthetic rate (A), stomatal conductance (g_s), the maximum stomatal conductance (g_smax), and the stomatal morphological parameters such as stomatal width and maximum stomatal area (a_max), all showed a downward trend. Under the S1 and S2 treatments, compared with the N0, the N1 treatment alleviated the stress effect of the Ssc on these indicators. However, under S3 treatment, the stress degrees of leaf water potential, g_s, g_smax and a_max, were aggravated after nitrogen application. This indicated that under the high Ssc of S3, the interaction between nitrogen application and soil salinity should be considered. WUE_in increased with the increase in Ssc. Moreover, under N1 treatments, the increase in WUE_in with Ssc was greater than that with N0. With the increase in Ssc, whether nitrogen was applied or not, the dry weight of maize declined by 44.2% and 73.0%, respectively, for the S2 and S3 treatments. Under S2 treatment, N1 significantly improved the dry matter mass of maize compared with the N0 treatment. The results showed that soil salt stress can inhibit crop growth, physiology and dry matter accumulation, and that nitrogen application can alleviate this within a specific salinity range. Such results indicate that in saline-alkali areas, whether nitrogen fertilizer is applied or not should depend on the level of Ssc to improve plant growth.