Xiaosen Wang

In situ nondestructive continuous monitoring of plant water status coupled with online data analysis is a core technical prerequisite for developing intelligent irrigation decision-making systems. The LPCP (leaf patch clamp pressure probe, ZIM-probe) sensor can detect leaf turgor pressure and shows promising application prospects. In this paper, the LPCP was used to monitor the leaf turgor pressure of maize during the silky growth stage cultivated in the North China Plain. The experiment was arranged in a randomized block design with two treatments: full irrigation (CK) and natural drought (ND). The results showed that the probe output pressure (P_p) underwent three stages: P_{p min} increasing stage, P_{p max} early-occurring stage, and P_p curve inversion stage, along with soil water decreasing, which correspond to mild, moderate, and severe water stress, respectively, and the ranges of soil and leaf water content of each stage were identified. As water stress intensified, the peak times of transpiration rate and stomatal conductance occurred earlier than normal, and the values decreased; meanwhile, the relationships between P_p, sap flow (SF), and leaf physiology indicators were quadratic parabolic, but the parabola opening directions, determination coefficients of regression equations, and model significance differed under different water stress stages. Under mild and moderate water stress, P_p positively correlated with SF, vapor pressure deficit (VPD), photosynthetically active radiation (PAR), and air temperature (T), while negatively correlated with relative humidity (RH), and path analysis results revealed that PAR and T exerted direct effects on P_p variations, whereas SF and VPD influenced P_p indirectly through other variables, and RH exhibited a negative effect on P_p changes. However, these correlations reversed under severe water stress. A regression model including PAR, T and VPD was established to simulate the P_p values of maize under full irrigation conditions, and by comparing the variation trend of P_p curves between the predicted and the measured values, whether maize was under water stress could be determined.

Reducing irrigation and nitrogen fertilizer application while maintaining crop yields is crucial for sustainable agriculture in the North China Plain. To investigate the effects of irrigation and nitrogen application on above-ground nitrogen accumulation (ANA), yield, water consumption, and the water and nitrogen use efficiency of drip-irrigated winter wheat, a three-season field experiment was conducted with four levels of nitrogen fertilizer application (250, 167, 83, and 0 kg hm⁻², referred to as N3, N2, N1, and N0, respectively) and three levels of irrigation (80, 60, and 40 mm per irrigation event, referred to as W3, W1, and W1, respectively). Additionally, a control treatment (CK) was set up with almost no irrigation (only 10 mm of fertilizer water for topdressing was applied) at the N3 application level. The results indicated that over the three seasons, the average yield of irrigation treatments was 35.3% higher than that of the CK treatment under the N3 condition. Both irrigation and nitrogen application improved wheat yield and ANA; however, when irrigation exceeded W2 or nitrogen application exceeded N2, their positive effects were negligible. Due to the seasonal depletion of soil nitrogen by low-nitrogen treatments (N1 and N0), along with their other negative effects on soil health, the yields and ANA of N1 and N0 treatments gradually declined over seasons. Increased irrigation promoted evapotranspiration (ET), and when nitrogen application did not exceed N2, higher nitrogen levels also enhanced ET and soil water consumption within ET. Moderately reducing irrigation can enhance water use efficiency (WUE); however, extreme water scarcity can also decrease WUE. Compared to higher irrigation and nitrogen application treatments, the W2N2 treatment showed no significant decrease in either yield or WUE, along with an increase in NPE. Moreover, the NPFP of the N2 treatment was higher than that of the N3 treatment. Consequently, the W2N2 treatment is recommend as the optimal irrigation and nitrogen management strategy under the experimental conditions.

Reducing the nitrogen (N) application rate and improving water-use efficiency (WUE) are extremely important for sustainable agricultural development in wheat–maize rotation systems in the North China Plain (NCP). We conducted a three-year experiment to investigate the effects of the N application rate on the water-use characteristics of wheat–maize rotation systems in the NCP. The experiment consisted of four N application rates: 250, 167, 84, and 0 kg hm⁻², denoted by N3, N2, N1, and N0, respectively. The results showed the following: For the 0–60 cm soil layer, N deficiency could lead to reduced soil water use (SWU) in wheat seasons, but in maize seasons, N deficiency showed no significant effects on SWU in the 0–60 cm layer. For the 60–140 cm soil layer, N deficiency could lead to reduced SWU in wheat seasons, but in maize seasons, the effects of N deficiency on SWU in the 60–140 cm layer varied with the SWC in the 0–60 cm layer. Throughout the three-year experiment, the evapotranspiration (ET), leaf area index (LAI), yield, and WUE of plants receiving low N treatments decreased with the growing season due to the negative effects of low N treatment (N1 and N0) on the soil. The LAI, total ET, grain yield, and WUE were all positively correlated with each other for both wheat and maize. Considering grain yield and WUE, a single-season N application rate of 167 kg hm⁻² (N2 treatment) in the NCP could meet the growth needs of the wheat–maize rotation system.

Increasing planting density generally increases total water use by maize (Zea mays L.), but there are contrasting conclusions as well. To determine whether increasing planting density would increase total water use by maize, a 3-year field experiment was conducted in the North China Plain. In 2018, maize was planted at the four densities of 57,100, 66,700, 80,000, and 100,000 plants ha⁻¹. In 2019 and 2020, another four planting densities of 27,800, 41,700, 66,700, and 111,100 plants ha⁻¹ were selected. The results showed that increasing planting density increased leaf area index but decreased leaf stomatal conductance; maize grain yield reached the maximum at about 80,000 plants ha⁻¹. At the VE-V6 and R3-R6 stage, soil water use occurred mainly in the 0–60 cm soil layer, and planting density showed no effect on total soil water use by maize. At the V6-R3 stage, when soil water in the 0–60 cm soil layer was sufficient to meet the evapotranspiration demand, soil water use occurred mainly in the 0–60 cm soil layer; increasing planting density did not increase total soil water use. When soil water in the 0–60 cm soil layer was insufficient and could not meet the demand of evapotranspiration, soil water use in the 60–100 cm soil layer increased greatly and kept rising with increased planting density, resulting in elevated total soil water use. Therefore, we conclude that the effect of planting density on water use by maize varies with soil water content in the 0–60 cm soil layer in the North China Plain.