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Authors: Shao, M.; Advisor: -; Participants: Wang, Y.; Xia, Y.; Jia, X. (2018) - The Loess Plateau (LP) of China is a good representative area for critical zone (CZ) science studies. The LP is famous for its deep loess. In most areas, the thickness of the loess profile is deeper than 100 m, and two‐thirds of the area is arid and semiarid. With the Grain‐for‐Green project, the vegetation of the plateau has recovered gradually. However, with the increase in vegetative coverage, especially the planted vegetation, the water content of the soil profile has decreased and the soil is much drier. In this review, particular emphasis is paid to the dry conditions of deep soil, drought, regional restoration of vegetation, and effective management of soil moisture. We reviewed the progress of research on dried soil layers (DSLs) that resulted from soil drought in the past d...
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Authors: Doležal, F.; Advisor: -; Participants: Hernandez-Gomis, R.; Matula, S.; Gulamov, M.; Miháliková, M.; Khodjaev, S. (2018) - We selected 585 rainless days with regular records for the analysis of daily differences. On most days, the lysimeter‐measured actual evapotranspiration, ETa, was smaller than the Penman–Monteith FAO 56 reference crop evapotranspiration, ET0. The FAO 56 procedure was found to be a reasonable estimator of the unstressed evapotranspiration in a moderately stressed environment. The ETa/ET0 ratio and the canopy surface resistance, rs, depend on the soil water content and suction measured at 5 cm. These graphs break down into horizontal unstressed parts and declining (for ETa/ET0) or inclining (for rs) water‐stressed parts. The ratio ETa/ET0 is about 85% and rs is about 250 s m−1 when the grass is not under water stress. The annual curve of the unstressed crop coefficient has a sine shap...
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Authors: Ruth, C.E.; Advisor: -; Participants: Michel, D.; Hirschi, M.; Seneviratne, S.I. (2018) - The resulting water‐balance estimates were then compared with those of the lower resolution large lysimeter, whose processing has remained unchanged since its installation. A number of additional, retrospectively applicable processing steps for the large lysimeter were then tested to mitigate the main sources of error for this instrument. Those found to be most beneficial were the application of a 10‐min moving average to the mass measurements and the setting of ET and condensation to zero in hours with liquid precipitation. In spite of the differences in design, a generally close agreement between the two lysimeters was observed, which was further improved with the optimized large‐lysimeter processing. A comparison of the lysimeter mass increases associated with liquid precipitatio...
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Authors: Teuling, A.J.; Advisor: -; Participants: - (2018) - In spite of the large number of studies on the role of forests in affecting local and global water and energy cycles, conflicting reports on even the sign of the change in evapotranspiration over forest compared with non‐forest land cover can be found depending on the type of data used. Whereas studies based on closure of the water balance suggest higher evapotranspiration over forests, studies based on turbulent exchange and/or energy balance closure suggest generally higher latent heat flux over non‐forest sites. In this study, this forest evapotranspiration paradox was investigated using data from four long‐term lysimeter stations in western Europe with contrasting land cover conditions. The results were consistent with evapotranspiration estimates from catchment‐scale water bala...
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Authors: Molénat, J.; Advisor: -; Participants: Raclot, D.; Zitouna, R.; Andrieux, P.; Coulouma, G. (2018) - The observation strategy is motivated by monitoring water, sediment, and contaminant fluxes and hydrologic and climatic variables at different spatial scales from cultivated plots and landscape elements to the catchment scale. These measurements have been performed at a fine time resolution over a long‐term scale and by surveying land use, agricultural practices, and soil surface characteristics. The long‐term observation strategy intends to support integrative multidisciplinary research for elucidating the conditions that improve soil and water management and delivery of ecosystem services in a Mediterranean rainfed cultivated context. The observatory has led to scientific insights regarding three scientific objectives: (i) to better understand the fluxes of water, erosion, and con...
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Authors: Cai, C.; Advisor: -; Participants: Vanderborght, J.; Couvreur, V.; Mboh, C.M.; Vereecken, H. (2018) - These models were implemented in HYDRUS‐1D, and soil hydraulic parameters were optimized by inverse modeling using soil water content and potential measurements and observations of root distributions of winter wheat (Triticum aestivum L.) in horizontally installed rhizotubes. Soil moisture was equally well predicted by the three models, and the soil hydraulic parameters optimized by the models with compensation were comparable. The obtained RWU parameters of the Feddes–Jarvis model were consistent with data reported in the literature, although the pressure heads h3l and h3h for lower and higher transpirations rates, respectively, could not be uniquely identified. Response surfaces of the objective function showed that the root‐related parameters of the Couvreur model could be identi...
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Authors: Berezniak, A.; Advisor: -; Participants: Ben-Gal, A.; Mishael, Y.; Nachshon, U. (2018) - Drip irrigation is a useful method for the application of low‐quality water because it does not wet the foliage and limits the spread of contaminants. Nevertheless, when using water containing high levels of dissolved salts, drip irrigation may be insufficient for leaching and can lead to soil salinization. A new conceptual model was tested experimentally and numerically to examine if manipulation of the distribution of soils with different textures could promote the removal of salts from the root zone and increase leaching efficiency. The manipulated root zone consisted of a volume of coarse soil, located under a drip irrigation emitter, surrounded by finer texture soil. We hypothesized that the differences in hydraulic properties between the two soils and the capillary barrier dev...
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Authors: Yang, H.; Advisor: -; Participants: Du, T.; Mao, X.; Shukla, M.K. (2020) - Results indicated no changes in leaf photosynthesis rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) up to 2 dS m−1 irrigation water salinity. Nonlinear models better described tomato yield and seasonal ET. The proposed new model performed best when compared with four previous models to predict tomato yield and ET responses to salinity. The calculated soil salinity threshold values (ECe*) from the new model were 1.73 dS m−1 for yield and 2.52 dS m−1 for ET. Data from published studies on effects of irrigation water salinity (ECw) on tomato yield and ET were analyzed to validate models. The results showed that the new model was simpler and superior in estimating plant responses to ECw. Tomato is a salt‐sensitive crop, and irrigation with brackish waters adversely inf...
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