Irrigation Scheduling and Crop Water Relations

Drought has become one of the major constraints to agricultural development, particularly in areas that lack water. Studying the effects of different water stresses on the photosynthesis, growth, yield, water use efficiency (WUE) and irrigation water productivity (IWP) of winter wheat will provide data for the development of scientific irrigation strategies for water-saving agricultural methods. According to the size of the field water capacity, four different water stress levels were set, i.e., 30–40% (severe stress), 40–50% (moderate stress), 50–60% (mild stress) and 60–80% (well-watered) of field water capacity, controlling the amount of irrigation through an automatic irrigation system. The results showed that the seasonal changes in photosynthetic parameters, such as net photosynthetic rate (Pn), intercellular carbon concentration (Ci), stomatal conductance (Gs) and transpiration (E), significantly decreased under moderate and severe stress. As a result, the height, biomass and grain size of winter wheat decreased significantly, which led to low WUE and IWP. The Pn of the mild stress group only slightly decreased compared to that of the well-watered group, and was actually higher during the flowering and grain-filling stages, resulting in increases in dry biomass and 1000 grain weight of 2.07% and 1.95%, respectively. Higher WUE and IWP were attributed to higher yields and less water use. Thus, mild stress (60–80% field water capacity) resulted in the optimal use of water resources without a significant reduction in yield in the North China Plain (NCP). Therefore, mild stress can be considered a suitable environment for winter wheat growth in arid areas. Full article

Understanding the response of crop growth to water and fertilizer is helpful to improve their management and use efficiency. Three water and fertilizer coupling treatments were designed to carry out a two-season trial on two cabbage (Brassica oleracea L. var. capitata) cultivars in spring and autumn in the Beijing–Tianjin–Hebei region. The irrigation timings of the three treatments were controlled by the soil moisture content of 0–20 cm soil layer. Treatment 1 (L_WH_F): when the soil moisture content was decreased to 75% of the field capacity (θ_f), irrigation was carried out (i.e., the lower limit of irrigation was 75%θ_f), the critical soil moisture content for stopping irrigation was 90%θ_f (upper limit of irrigation), and the nitrogen (N) application amount was 400 kg/ha; treatment 2 (H_WL_F): the lower and upper limits of irrigation were 85%θ_f and 100%θ_f, respectively, and the N application amount was 200 kg/ha; and treatment 3 (M_WM_F): the lower and upper limits of irrigation were 75%θ_f and 100%θ_f, respectively, and the N application amount was 300 kg/ha. The results showed that the yield and its related parameters of cabbage in spring were higher than those in autumn because of the use of different cultivars and seasons. The growth indices of H_WL_F and M_WM_F in the two seasons were larger than that of L_WH_F, and the yields of H_WL_F were the highest, 78.37 t/ha (spring) and 64.42 t/ha (autumn), respectively. The nitrogen use efficiencies (NUEs) of L_WH_F in spring and H_WL_F in autumn were the highest, 213.29 kg/kg and 391.83 kg/kg, respectively. In general, there were statistically significant differences in the cumulative increment in plant height, stem diameter and leaf area in the two-season trial, yield in autumn and NUE in spring among the three treatments. In addition, there was a significant positive linear correlation between almost all indices in different growth stages and the corresponding evapotranspiration (ET_i). It is suggested that the application of drip irrigation under mulch should be approximately 114.7–125.0 mm, and the N fertilization should be about 200 kg/ha. Full article

The growth of Eucalyptus pellita in forestry plantations requires attention to water requirements, especially in the initial growth phase from seedling to field-ready plant. In this study, actual evapotranspiration (ET_a), crop coefficient (K_c), and the irrigation requirement of E. pellita were assessed during the nursery growth phase (day 40–142). The experimental set-up included lysimeters with different treatments in terms of plants, drainage, and soil conditions. Plant growth and water balance were monitored during June September 2018 in an open nursery area in Riau, Indonesia. ET_a was determined by the water balance lysimeter method and potential (reference) evapotranspiration (ET_o) was extracted based on the Penman-Monteith method (FAO/56). The results showed that the average K_c value for E. pellita at age 40–142 days is 0.79, which exceeds that reported for E. grandis. The recommended irrigation requirement varies depending on precipitation, from 70 mL/plant/day with no rainfall to zero at precipitation of >30 mm/day. This is the first study to assess water use in E. pellita growing in pots during the nursery phase, which provides guidance on irrigation requirements during their initial growth phase. Full article