Junfang Niu

Due to limited freshwater availability for winter wheat and summer maize, grain production in the annual double-cropping system of the low plain surrounding the Bohai Sea in North China is strongly influenced by inter-annual rainfall variability. The relatively abundant saline water resources in this region offer a potential source for irrigation. This study aimed to evaluate the effects of additional saline water irrigation under deficit irrigation on the crop yields and water productivity of winter wheat and its following crop maize, as well as to determine the soil salinity dynamics and annual salt balance under saline irrigation. A two-year field experiment (2023–2025) was conducted using six irrigation treatments, namely rainfed (I0), one freshwater irrigation (If), one saline irrigation (Is), combinations of freshwater and saline irrigation (Is + If, If + Is), and two freshwater applications (If2) to evaluate the effects of an additional saline water irrigation event, compared with the commonly used freshwater irrigation regime, on crop yields, water productivity, and the soil salt balance. The results showed that a single saline irrigation event (70 mm) increased the wheat yield by 18–38% under rainfed conditions and by 7–10% under limited freshwater irrigation. In contrast, the maize yield was not affected by the additional saline irrigation applied during the winter wheat season. Although salt accumulation occurred in the topsoil following the saline irrigation of winter wheat, it did not impair maize growth, owing to salt leaching during irrigation for maize emergence and concentrated summer rainfall. Within the two-year observation period, no progressive salt accumulation was observed in the top 1 m soil profile. These findings indicate that the strategic use of saline water to supplement the crop water supply can enhance crop production under deficit irrigation, provided that soil salinity is effectively managed.

The objective of this paper is to perform drip irrigation scheduling for spinach (Spinacia oleracea L.) in a plastic greenhouse using the standard 20 cm evaporation pan. A drip irrigation experiment with four levels of irrigation, i.e., 0.6, 0.8, 1.0, and 1.2 times the cumulative evaporation of a 20 cm standard pan (Epan) were set up. The irrigation interval was controlled using a 20 mm Epan, and optimal irrigation water amounts of 0.8 Epan and 0.6 Epan were recommended for the spring and autumn growing seasons, respectively. Overirrigation (1.2 Epan) also led to yield losses, particularly for stem growth. In addition, a proper greenhouse index, defined as the ratio of the cumulative Epan inside and outside the greenhouse, could predict the Epan inside the greenhouse using the external Epan to a high degree of accuracy (daily data with r² = 0.85, root mean square error (RMSE = 0.68 mm d⁻¹), for a 4-day interval with r² = 0.95, RMSE = 1.81 mm 4 day⁻¹, and for the entire growth period with r² = 1.0, RMSE = 2.40 mm). A simple and low-cost greenhouse index method could be used to formulate drip irrigation schedules for spinach in low-technology plastic greenhouses using a 20 cm standard pan outside the greenhouse.

Climate changes show asymmetrical warming, and warming is typically greater at night than during the day. To understand how nocturnal warming (NW) affects the performance of maize (Zea mays L.), an open-field experiment with a free air temperature increase (FATI) facility was conducted for three seasons during 2014 to 2016 at Luancheng eco-agro-experimental station on the North China Plain (NCP). Three nocturnal warming scenarios were set up: the entire growing period (T1, from V4 to maturity), only the vegetative stages (T2, from V4 to a week presilking) and the reproductive stages (T3, from a week presilking to R6). The treatment without NW was the control. Maize lodged seriously in 2015 due to heavy rainfall combined with strong winds, and the experiment failed. The results from 2014 and 2016 were analyzed in this study. During the experimental duration, the average nocturnal temperature was increased by approximately 3.6 and 3.3 °C at 150 cm height and 2.0 and 1.7 °C at the soil surface during the vegetative stages. The corresponding increases were 2.1 and 2.5 °C and 0.7 and 1.2 °C at the soil surface during the reproductive stages in 2014 and 2016, respectively, as compared with that of the CK treatment. NW during the whole growth period significantly decreased maize yield for the two seasons. Treatment T2 had a smaller impact on maize yield than T1 and T3. The silking stage was delayed by 2 days in 2014 and 2016 under T1. As a result, presilking duration and VT-R1 interval were prolonged by 1–2 days; and the postsilking duration were shortened by 1–3 days under T1. The soil moisture in the warmed plots was slightly lower than that in the control plots in the 2014 and during the stages before the earlier grain-filling stages in 2016, but NW decreased soil water content greatly at the later grain-filling stages in 2016, which caused the fast green leaf senescence and exacerbated the negative effects of NW on maize yield. NW for the whole growth duration (T1) significantly decreased seed weight and harvest index. NW increased leaf nighttime respiration rate in both seasons. No significant effects of NW on ear leaf net photosynthesis, leaf area, and specific leaf weight at early grain-filling stage were observed, irrespective of the warming stage and season. The results suggested that reproductive stages were more sensitive to NW compared to vegetative stages under the growing conditions of NCP. The negative effects of NW were worsened in dry seasons. The reduction in maize yield with nocturnal warming was driven by the reduction in the aboveground carbon allocation from shoot to grain during postanthesis stage.