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  • BB

  • Magnetic Resonance Monitoring and Numerical Modeling of Soil Moisture during Evaporation

    • Authors: Merz, S.;  Advisor: -;  Participants: Balcom, B.J.; Enjilela, R.; Vanderborght, J.; Rothfuss, Y.; Vereecken, H.; Pohlmeier, A. (2018)

  • Evaporation from bare soil surfaces can be restrained to a great extent with the development of a dry layer at the soil surface where capillary hydraulic conductance ceases and water flow proceeds only by gas phase transport. Model calculations and preliminary experiments with model porous media have shown that this surface layer can be very thin. An accurate characterization of these processes is required, which is provided by noninvasive magnetic resonance (MR) methods. The evaporative drying of a silt loam and a sandy loam was monitored at high spatial resolution in laboratory experiments. The MR data were used to assess the performance of two numerical models: (i) the Richards equation, which considers isothermal liquid water flow, and (ii) a coupled soil water, heat, and vapor ...
  • BB

  • Simulation of spatial variability in crop leaf area index and yield using agroecosystem modeling and geophysics‐based quantitative soil information

    • Authors: Brogi, C.;  Advisor: -;  Participants: Huisman, J. A.; Herbst, M.; Weihermüller, L.; Klosterhalfen, A.; Montzka, C.; Reichenau, T. G.; Vereecken, H. (2020)

  • Soil hydraulic parameters were calculated using pedotransfer functions. Simulations of soil water content dynamics performed with the agroecosystem model AgroC were compared with soil water content measured at two locations, resulting in RMSE of 0.032 and of 0.056 cm3 cm−3, respectively. The AgroC model was then used to simulate the growth of sugar beet (Beta vulgaris L.), silage maize (Zea mays L.), potato (Solanum tuberosum L.), winter wheat (Triticum aestivum L.), winter barley (Hordeum vulgare L.), and winter rapeseed (Brassica napus L.) in the 1‐ by 1‐km study area. It was found that the simulated leaf area index (LAI) was affected by the magnitude of simulated water stress, which was a function of both the crop type and soil characteristics. Simulated LAI was generally consist...
  • BB

  • Simultaneous multichannel multi‐offset ground‐penetrating radar measurements for soil characterization

    • Authors: Kaufmann, M.S.;  Advisor: -;  Participants: Klotzsche, A.; Vereecken, H.; van der Kruk, J. (2020)

  • Recently, a novel simultaneous multi‐offset multichannel (SiMoc) GPR system was released, enabling rapid profiling with virtually continuous acquisition of WARR gathers. For this system, we developed a new processing approach. First, time shifts caused by the different cables and receivers were eliminated by a novel calibration method. In the obtained CMP gathers, groundwave and (when present) reflection velocities were determined with an automated semblance approach. The obtained velocity can be converted to permittivity and soil water content. We tested SiMoc GPR with a synthetic study and time‐lapse field measurements. In the synthetic study, the accuracy of velocity and layer thickness were within 0.02 m ns−1 and 2 cm. The SiMoc field results (spatial sampling of 5 cm) are consi...
  • BB

  • On the impact of increasing drought on the relationship between soil water content and evapotranspiration of a grassland

    • Authors: Rahmati, M.;  Advisor: -;  Participants: Groh, J.; Graf, A.; Pütz, T.; Vanderborght, J.; Vereecken, H. (2020)

  • All components of the water balance were determined from 2012 until 2018. Budyko analysis was used to characterize the hydrological status of the studied sites. Wavelet analysis was also applied to study the power spectrum of ETa, vegetation‐height‐adjusted reference evapotranspiration (ETcrop), and water stress index (WSI) defined as ETa/ETcrop, as well as SWC at three different depths and the coherence between SWC and ETa and WSI. The Budyko analysis showed that 2018 resulted in a shift of both locations towards more water‐limited conditions, although Rollesbroich remained an energy‐limited system. Based on the power spectrum analysis, the annual timescale is the dominant scale for the temporal variability of ETa, ETcrop, and SWC. The results also showed that increasing dryness at...
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  • Soil hydraulic properties estimation from one‐dimensional infiltration experiments using characteristic time concept

    • Authors: Rahmati, M.;  Advisor: -;  Participants: Vanderborght, J.; Šimůnek, J.; Vrugt, J.A.; Moret‐Fernández, D.; Latorre, B.; Lassabatere, L.; Vereecken, H. (2020)

  • We demonstrate the usefulness and power of the CTM by comparing it with a suite of existing methods using synthetic cumulative infiltration data simulated by HYDRUS‐1D for 12 synthetic soils reflecting different USDA textural classes, as well as experimental data selected from the Soil Water Infiltration Global (SWIG) database. Results demonstrate that the inferred values of S and Ks are in excellent agreement with their theoretical values used in the synthetically simulated infiltration experiments with Nash–Sutcliffe criterion close to unity and RMSE values of 0.04 cm h−1/2 and 0.05 cm h−1, respectively. The CTM also showed very high accuracy when applied on synthetic data with added measurement noise, as well as robustness when applied to experimental data. Unlike previously publ...
  • BB

  • Monitoring Soil Water Content Using Time‐Lapse Horizontal Borehole GPR Data at the Field‐Plot Scale

    • Authors: Klotzsche, A.;  Advisor: -;  Participants: Lärm, L.; Vanderborght, J.; Cai, G.; Morandage, S.; Zörner, M.; Vereecken, H.; van der Kruk, J. (2019)

  • The SWC data were analyzed for four growing seasons between 2014 and 2017, two soil types (gravelly and clayey–silty), two crops (wheat [Triticum aestivum L.] and maize [Zea mays L.]), and three different water treatments. We acquired more than 150 time‐lapse GPR datasets along 6‐m‐long horizontal crossholes at six depths. The GPR SWC distributions are distinct both horizontally and vertically for both soil types. A clear change in SWC can be observed at both sites between the surface layer (>0.3 m) and subsoil. Alternating patches of higher and lower SWC, probably caused by the soil heterogeneity, were observed along the horizontal SWC profiles. To investigate the changes in SWC with time, GPR and time‐domain reflectometry (TDR) data were averaged for each depth and compared with c...