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Understanding the impact of sprinkler irrigation on field energy balance, microclimate, and crop evapotranspiration is of great importance for optimizing irrigation scheduling and enhancing crop growth. In this study, the microclimate variables, energy, and water flux were measured using an eddy covariance system during four wheat (Triticum aestivum L.) growing seasons in a sprinkler-irrigated field of North China Plain. The variation patterns of microclimate, energy balance (net solar radiation Rn, soil heat flux G, latent heat LE, and sensible heat H) and crop evapotranspiration (ET) were analyzed during and after sprinkler irrigation events. A novel quantitative model using a stepwise regression method was developed to predict the change in microclimate after sprinkler irrigation by considering irrigation, weather, meteorology, and crop traits. The results showed that the reflectance rate of the wheat canopy decreased by 0.01, and the daily LE/Rn increased by 0.19–0.23 in the 1–3 days after sprinkler irrigation with 40–50 mm water, which finally resulted in crop ET increased by 1.8–4.7 mm during irrigation interval, and seasonal total ET could increase by 9–24 mm when five normal sprinkler irrigations were implemented in a wheat season. The mean daily H/Rn decreased by 0.06–0.17, indicating weak energy exchange between canopy and environment. The measured daily minimum (Tmin), maximum temperatures (Tmax) and daily mean vapor pressure deficit (VPD) decreased by approximately 0.8 °C, 0.9 °C, and 0.25 kPa, respectively, and daily mean relative humidity increased by approximately 7.5% on the first 3 days after sprinkler irrigation; and these changes decreased and were negligible on the 5th–7th days. The decreases in daily Tmin, Tmax, and mean VPD after sprinkler irrigation could change more under higher irrigation amounts and sunny days with a larger crop leaf area index based on the fitted models. [ABSTRACT FROM AUTHOR]

Hetao Irrigation District (HID) is characterized by less rainfall and high evaporative, but it is a main grain production region in China. Increasing water use efficiency is an appropriate way to fulfill the sustainable agriculture development because the allocated water for HID will be reduced in the future. In this study six irrigation treatments with irrigation amounts being the 20, 40, 60, 80, 100, and 120% of crop water requirement (ET c ) were carried out for maize crop ( Zea mays L.) in the HID under mulch-dripped irrigation condition in 2013 and 2014 years. Soil water and electrical conductivity, plant growth factors, harvest factors and yield were investigated, and crop actual evapotranspiration (ET cact ), water use efficiency (WUE) and irrigation water use efficiency (IWUE) were calculated. Results showed that soil water and salt mainly varied in the upper 60 cm soil layer. At harvest, salt accumulation was found in the upper soil layer and the highest salt accumulation was in the least irrigation treatment. Growth factors and harvest factors were reduced significantly (P < 0.05) for irrigation depth of less than 40%ETc compared to 80–120%ETc, but they were not significantly (P > 0.05) different from 80 to 120%ETc. The highest grain yield were found at 100%ETc, then yield decreased with irrigation depth decreasing due to the reductions of ear size and 100-grain weight. ET cact ranged from 200 to 430 mm in the two seasons, and linearly increased with the irrigation depth increasing. The highest WUE was found at 60%ETc, while IWUE was decreasing with irrigation depth increasing. Fully considering maize yield, water use efficiency, soil salt balance and water resources availability of Yellow river, full irrigation with 100%ETc is recommended with the objective of the highest yield when water resources can satisfy water demand of irrigation and economic development, while water deficit of 20–30% is recommended with the objective of getting the highest WUE and little yield loss (4–8%) under mulched drip irrigation in HID. [ABSTRACT FROM AUTHOR]

Shenzhen city was a farmland region before 1978, and it then developed to a mega city in China. This type of change in city can greatly affect the climatic conditions. In this study, the daily, monthly, and annual climatic variables and the reference crop evapotranspiration (ET0) for Shenzhen from 1954 to 2012 were computed using the FAO Penman-Monteith equation (PM), and these parameters were analyzed to study the temporal trends of ET0 and meteorological factors. The trends and the time points of abrupt changes of ET0 and meteorological factors were tested using Mann-Kendall methods. Results show that, in the past 59 years, the annual ET0 first decreased from 1954 to 1978, then increased from 1979 to 1990, and now varied slightly after 1990. The mean air temperature rose gradually, and the relative humidity decreased as a whole. These trends finally resulted in an increasing trend in vapor pressure deficit (VPD). The wind speed showed a slightly decreasing trend. Both the annual total sunshine duration and net radiation showed trends of rapid decline. ET0 change is sensitive to the hours of sunshine and VPD. The significant increase in ET0 after 1979 was mainly due to the increased air temperature and decreased relative humidity. [ABSTRACT FROM AUTHOR]

In this study, seven widely used potential evapotranspiration (ETo) methods were evaluated by comparing with the FAO-56 Penman-Monteith method (PM method) to provide useful information for selecting appropriate ETo equations under data-limited condition in Beijing, China. Statistical methods and parameters, namely linear regression, root mean squared error (RMSE) and mean bias error (MBE), were used to evaluate the seven ETo methods. Results showed that ETo estimated using Kimberly-Penman method have fairly close agreement with the PM method (referring to standard ETo), considering the coefficient of determination (R²) of 0.96, RMSE of 0.42 mm/day, and a coefficient of efficiency (E) of 0.96. Locally calibrated Penman and Doorenbos-Pruitt methods also have better agreement with the PM method, correspondingly with R² of 0.99 and 0.95, RMSEs of 0.24 mm/day and 0.21 mm/day, and coefficients of efficiency of 1.02 and 0.99, respectively. The ETo is the most sensitive to vapor pressure deficit (VPD) and net radiation in the Beijing area. Hence, the VPD-based and VPD-radiation combined ETo methods were developed and calibrated. Results showed that the two developed methods performed well in ETo estimation. By fully considering the data-limit situation, the calibrated Turc method, VPD-based method and VPD-radiation-combined method may be attractive alternatives to the more complex Penman–Monteith method in Beijing. [ABSTRACT FROM AUTHOR]

Aiming at investigating an appropriate irrigation management strategy that could lead to increase onions yields and improve water productivity (WP), a two-year field experiment was conducted in the arid region of Northwest China with drip irrigation and plastic mulch. Eight treatments were considered: four with different levels of water stress throughout the crop season, and four where water stress was applied at the establishment, development, bulbification and ripening stages. The seasonal actual evapotranspiration (ET), plant height, above-ground biomass, yield (total, high-quality and marketable quality yields) as well as related irrigation and total water productivity were determined. Plant heights, above-ground biomass and the referred yields have shown to be sensitive to water stress, particularly during the development and bulbification stages. Due to the importance of quality of horticultural products, the WP computed with the yields of high-quality bulbs revealed the most informative contrarily to the WP computed with the total yields. It could be concluded that water stress has to be avoided during the development and bulbification stages, and only small deficits are acceptable if applied throughout the crop season. [ABSTRACT FROM AUTHOR]

The solar greenhouse is a common protected structure for crop production when ambient temperatures are low. In the North China Plain (NCP) winter temperatures are very low and an improved solar greenhouse with a lowered soil surface (0.5–1.5 m deep), referred to as a sunken solar greenhouse (SSG), is used. A four-season experiment was conducted in a commercial SSG with tomato crops to characterize internal microclimate, sap flow (SF) and crop coefficients. Results show that temperature inside the SSG could be more than 20 °C higher than outside in winter, which favors tomato growth and resulted in acceptable yields. Daily total SF was related to solar radiation, vapor pressure deficit (VPD) and temperature, in that order, both in winter and summer. The decoupling coefficient (which is the ratio of radiative to aerodynamic influences on evapotranspiration) in daytime was 0.76 in winter and 0.84 in summer, indicating strong decoupling (i.e., predominance of radiative influences) of the internal environment where wind speed was low. Basal crop coefficients at the mid stage of crop growth averaged 1.15–1.43 in winter and 0.91–0.92 in spring and summer. Thus, in the SSG, for similar climatic conditions sap flow in winter was higher than that in summer, which should be considered in irrigation scheduling. [ABSTRACT FROM AUTHOR]

Abstract: The North China Plain (NCP) is one of the main productive regions for winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) in China. However, water-saving irrigation technologies (WSITs), such as sprinkler irrigation technology and improved surface irrigation technology, and water management practices, such as irrigation scheduling have been adopted to improve field-level water use efficiency especially in winter wheat growing season, due to the water scarcity and continuous increase of water in industry and domestic life in the NCP. As one of the WSITs, sprinkler irrigation has been increasingly used in the NCP during the past 20 years. In this paper, a three-year field experiment was conducted to investigate the responses of volumetric soil water content (SWC), winter wheat yield, evapotranspiration (ET), water use efficiency (WUE) and irrigation water use efficiency (IWUE) to sprinkler irrigation regimes based on the evaporation from an uncovered, 20-cm diameter pan located 0–5cm above the crop canopy in order to develop an appropriate sprinkler irrigation scheduling for winter wheat in the NCP. Results indicated that the temporal variations in SWC for irrigation treatments in the 0–60-cm soil layer were considerably larger than what occurred at deeper depths, whereas temporal variations in SWC for non-irrigation treatments were large throughout the 0–120-cm soil layer. Crop leaf area index, dry biomass, 1000-grains weight and yield were negatively affected by water stress for those treatments with irrigation depth less than 0.50E, where E is the net evaporation (which includes rainfall) from the 20-cm diameter pan. While irrigation with a depth over 1.0E also had negative effect on 1000-grains weight and yield. The seasonal ET of winter wheat was in a range of 206–499mm during the three years experiments. Relatively high yield, WUE and IWUE were found for the irrigation depth of 0.63E. Therefore, for winter wheat in the NCP the recommended amount of irrigation to apply for each event is the total 0.63E that occurred after the previous irrigation provided total E is in a range of 30–40mm. [Copyright &y& Elsevier]

In north China, vegetables are always cultivated in conventional solar greenhouses (SG), however, these structures cannot be used during most of the winter due to extremely low temperatures. In this study, a new type of a solar greenhouse named sunken solar greenhouse (SSG), where the inside soil surface is lowered 1–2 m below outside and the back wall is 5–8 m width at the bottom and 1.5–2 m on top, was investigated. Inside climatic variables were recorded and compared with those outside during seven cucumber cultivation seasons. Crop evapotranspiration (ETc) was estimated using the Penman–Monteith method. Results show that inside solar radiation was reduced by approximately 40%, however days with a daily maximum inside temperature higher than 20 °C accounted for 80–90% of the days during the winter, which greatly enhanced cucumber fruit production compared to common SGs. The reference crop evapotranspiration (ETo) inside the SSG was reduced by 27% compared to outside. The estimated ETc was generally lower than 4 mm day−1, which resulted in a basal crop coefficient of 0.83. In conclusion, the SSG is environmental-friendly, preferable for winter vegetable cultivation in north China, and can be useful for other regions of the world with cold winter conditions. [ABSTRACT FROM AUTHOR]

Highlights: [•] We assessed crop coefficients for maize in semi-arid Hailiutu catchment, China. [•] Plant sap flow (SF) and soil evaporation were measured, and summed to obtain ET c . [•] ET c was estimated with the Penman–Monteith equation and an FAO crop coefficient (K c ). [•] Estimated and measured evapotranspiration rates agreed well. [•] Groundwater contributed 33% and 27% of maize ET c in 2011 and 2012, respectively. [ABSTRACT FROM AUTHOR]