查看更多>>摘要：? 2021 Elsevier B.V.Under the background of climate warming, the global water cycle is gradually accelerating, which will lead to increased drought frequency and severity. China is one of the countries with the highest drought risk and the most serious drought impact, accompanied by abnormal and variable drought characteristics in recent decades. However, the dynamic variation of meteorological drought and its complicated relationships with agricultural drought are still unclear across China. In this study, the characteristics of meteorological drought were comprehensively identified across China during 1960–2019. The spatio-temporal variations and gridded trend characteristics of meteorological drought were revealed during the study period. Subsequently, the return period of meteorological drought was quantitatively determined based on copula models. Finally, the relationships between meteorological and agricultural drought were explicitly clarified. The results indicated that: (1) meteorological drought showed an increasing trend across China from 1960 to 2019, especially since the 1990s; (2) the most serious meteorological drought occurred in 2011, with a minimum standardized precipitation evapotranspiration index (SPEI) value of –0.81; (3) the percentage of drought area (PDA) with an increasing trend in spring, summer, autumn and winter was 85.8%, 77.4%, 97.7% and 12.9%, respectively; (4) the most appropriate copula model of meteorological drought severity and duration was Frank copula; and (5) the propagation time from meteorological to agricultural drought was longer in winter and shorter in summer, which can determine the appropriate irrigation period and predict the occurrence of agricultural drought. This study sheds new viewpoints into the identification of meteorological drought variation and its relationships with agricultural drought, which can also be applied in other areas.
查看更多>>摘要：? 2021 Elsevier B.V.Nitrogen (N), phosphorus (P) and potassium (K) are essential elements for crop growth. The absorption, accumulation process and distribution of these nutrients affect not only the growth and grain yield, but also the grain quality of wheat (Triticum aestivum L.). Various fertilization and irrigation practices can influence wheat growth as well as the absorption and utilization of nutrient elements. A four-season (2014–2018) experiment was conducted on drip-fertigated winter wheat on the Loess Plateau of China with three irrigation levels and three fertilization rates. Irrigation rates included normal irrigation (W1), mild deficit irrigation (W2) and more severe deficit irrigation (W3), while fertilization rates (N-P2O5-K2O) included F1 (175–117–150 kg ha?1), F2 (125–84–108 kg ha?1) and F3 (75–50–65 kg ha?1). The results showed that NPK uptake in aboveground biomass decreased as the water stress increased, but there was no significant difference between W1 and W2. When sufficient water and fertilizer were applied, the stem, leaf and rachis + glume obtained higher proportion of NP, while grain nitrogen and phosphorus harvest index (NHI and PHI) decreased. When the supply of water and fertilizer was insufficient, NHI and PHI increased, and the proportion of vegetative organs was relatively low. The average NPK requirement for 100 kg grain (GNR, GPR and GKR) varied 1.93–3.03, 0.37–0.41 and 2.26–2.93 kg over the four seasons. GNR and GKR increased with increasing irrigation and fertilization regimes. With the increase of irrigation amount, irrigation water use efficiency (IWUE) first increased and then decreased slightly, and the maximum IWUE occurred under W2. Yield and IWUE increased with the increase of fertilization rate, but there was no significant difference between F1 and F2. F2 obtained higher partial factor productivity than F1. F1 and F2 had no significant difference in protein content and protein yield, but they obtained significantly higher values than F3. Therefore, W2F2 was an efficient water and fertilizer management practice for drip-fertigated winter wheat, which promoted nutrients transfer to grains without significantly reducing grain yield and protein.
查看更多>>摘要：? 2021 Elsevier B.V.Soil moisture (SM) is an important indicator of the photosynthetic rate and growth status of crops. A few related parameters, such as the red-edge parameters and spectral indices, have been adopted for retrieving the SM of winter wheat. To further study their abilities to detect the SM, field-scale water stress experiments on winter wheat were conducted during the 2018/19 growing season. The spectral ratio index in the near-infrared (NIR) shoulder region (NSRI) (700–1100 nm) was selected by comparing the correlations between the SM and the red edge parameters and spectral indices, and it was optimized using the partial least squares regression (PLSR) method. To assess the performance of the sensitive wavebands of the NSRI in retrieving the SM, three types of spectral index models were established using multiple linear regression (MLR) for the winter wheat from the jointing to the ripening stage. The results indicate that the red-edge parameters are more sensitive to the spectral variation during the jointing and flowering stages. The sensitivity decreased with increasing water stress. The red-edge area (SDr) of winter wheat irrigated in the flowering stage (D1 treatment) and irrigated in the jointing stage (D2 treatment) decreased by 20–30%, respectively. In general, all of the parameters and indices were correlated with the surface SM (0–40 cm depth), especially for the NSRI, with a significant coefficient of determination (R2) of 0.52 in the 10–20 cm depth interval (P < 0.01). Moreover, all of the spectral index models based on the optimized NSRI have good capabilities for retrieving the SM in the jointing stage. The model for one derivative of the logarithm of the NSRI (logarithmic NSRI)' performed best, with R2 and root mean square error (RMSE) values of 0.81–0.92 and 0.17–0.89%, respectively. Finally, the (logarithmic NSRI)' model was used to retrieve the SM in the flowering–ripening stage (R2 =0.85). Overall, the optimized spectral index models can accurately and quickly retrieve the SM and can assist in predicting the effect of drought on the crop yield in the future.
查看更多>>摘要：? 2021In the Texas High Plains (THP), groundwater resources for irrigation are declining because of aquifer depletion and reduced well yield. Inability to meet peak water demands of maize under constrained irrigation capacities decreases yield and profitability. The MOPECO crop model, calibrated for the THP, was adapted to simulate maize water use and yield under center pivot irrigation to evaluate water allocation strategies under limited irrigation. Simulations were carried out over a range of irrigation capacities (3 – 12 mm d-1 for a 50.9 ha area), initial soil water contents, and application depths with irrigation allocated to a fraction (0.5 – 1.0) of the pivot area. Fractional water allocations were achieved by withholding irrigation from circular sectors or from outer spans with unirrigated fractions in fallow or planted to dryland cotton. These strategies were evaluated for growing seasons characterized by typical meteorological years with average (TMY1), average to above average (TMY2), and below average (TMY3) precipitation. Preseason irrigation had little to no influence on grain yield at irrigation capacities ≥ 5 mm d-1. At irrigation capacities ≤6 mm d-1 under TMY1, marginally greater yields 50.9 ha-1 were simulated when a fraction was irrigated. For irrigation capacities ≤8 mm d-1 under TMY1, reducing the irrigated area was the most prudent option to optimize net returns. As irrigation capacities increased from 4 to 8 mm d-1, the irrigated fraction that maximized net returns increased from 0.5 to 0.9. Concentrating water generated greater net returns because of greater irrigation water productivities and lower seed and fertilizer costs. Compared with fallow, planting cotton in the unirrigated portion increased net returns except in years with a seasonal drought (TMY3). Because greater irrigation volume did not always increase net returns, there is an opportunity to both increase profitability and conserve water by irrigating a fraction of the area.
查看更多>>摘要：? 2021 The AuthorsA widely promoted approach to tackle food insecurity and water shortage challenges simultaneously is to enhance crop water productivity (WP). Therefore, multiple international organizations have featured WP improvements as their major policy goal, and substantial public and private investments have been made in this domain. Advances in remote sensing allow accurate, rapid, and cost-effective WP analysis for agricultural monitoring. However, translating the data to actionable information seems fraught with difficulties, as it only provides spatial and temporal variability in WP and no information on the causes of the variability. This paper introduces a standard approach using open-source remote sensing data for diagnosing reasons behind WP variations, comparing high performing fields (bright spots) with low performing fields (hotspots). The framework is applied to a case study on the Bekaa Valley in Lebanon considering wheat, potato and table grapes. Six factors (crop water stress, irrigation uniformity, soil salinity, nitrogen application, crop rotation and soil type) were analysed to identify their influence on WP and yield. This paper reveals that the growth of wheat and potatoes is negatively affected by water stress in the critical crop growth stages, non-uniform irrigation and nitrogen stress. Also, it was found that potatoes grown on clay-loam soil has better WP and yield than potatoes grown loam soil. Such information with regard to WP factors assists practitioners to identify priority areas and actions aiming at cropfield level WP improvement. While acknowledging errors, uncertainties and caveats inherent to the use of remote sensing data, this paper shows the feasibility and practical usefulness of the diagnostic framework.
查看更多>>摘要：? 2021 Elsevier B.V.Saline water irrigation can alleviate the deficiency of agricultural freshwater resources, especially in arid regions. However, saline water may lead to soil salinization and affect crop quality. A water-salt regulation (WSR) irrigation method has been developed to avoid soil salinization. To investigate the effect of saline water irrigation on crop quality while maintaining soil salinity balance, we conducted a field experiment on tomatoes under the WSR method in the arid region of northwest China from 2018 to 2019. Five treatments with electrical conductivity (ECi) of 0.5 dS/m, 3.1 dS/m, 4.7 dS/m, 6.2 dS/m, and 7.8 dS/m were designed, where ECi indicates salinities of irrigation water. We applied the WSR method for all five treatments to maintain the soil matric potential (SMP) above ? 20 kPa at a depth of 20 cm below drip emitters. The results from three aspects (quality, yield, and soil salinity) are as follows: (i) Saline water irrigation can improve tomato quality, as evidenced by increasing the content of soluble solids, reducing sugar, organic acid, and vitamin C. When ECi ranged from 4.7 dS/m to 7.8 dS/m, the sugar-acid ratio was in the appropriate scope (7.4–9.8). (ii) The commercial yield and total yield declined by 4.8% and 4.4% as the ECi increased 1 dS/m. (iii) the soil salinity can be kept balanced under the WSR method after a 2-year experiment when the ECi of saline water did not exceed 4.7 dS/m. Therefore, in similar arid areas with a lack of freshwater resources, saline water of 4.7 dS/m under the WSR method can be used to irrigate field-grown tomatoes, compensating for the reduced yield by improving quality.
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