CRNS and root zone soil moisture dynamics in agricultural land

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The focus of this project builds on work done in GW in the first phase of the research unit Cosmic Sense which has mainly dealt with the use of CRNS for estimating groundwater recharge and the influence of soil moisture profile shape on CRNS interpretation. Field scale recharge rates at daily basis could be estimated by the use of 1D vadose zone models, and several ways to integrate CRNS within such models were tested. Accompanying measurements were designed and a simple approach developed to compensate for the vertically decreasing sensitivity of the sensor in respect to heterogeneous soil moisture profiles.Within the second phase the research on the influence of different vertical soil moisture distributions on the signal generation and penetration depth of the sensor will be extended for close to natural conditions to highly-managed systems, mainly for an agricultural land use. To achieve this, CRNS measurement will be evaluated, if existing already, or performed at different field sites impacted by shallow groundwater within the CRNS penetration depth or by dedicated artificial sprinkling irrigation experiments in cropped fields. This large band width of vertical soil moisture distributions will be the basis for a systematic assessment of the CRNS penetration depth where related to agricultural applications.The fundamental understanding of vertically heterogeneous distribution of water within the rooted soil profile and the CRNS variable penetration depth will enable to target a more comprehensive view on water storage and fluxes in the rooted soil zone based on CRNS measurements, e.g. at a field site with controlled groundwater table levels and drainage conditions. With that a larger focus shall be set on CRNS and plant-soil interaction, and thus the roots of vegetation as driving water storage changes, being decisive for replenishment of the deeper subsoil layers after drought and groundwater recharge. Also, they themselves are potentially affected by water stress and creating irrigation demands, and its management can be supported by CRNS-based measurements or modeling. Measurements and simulations of soil moisture profiles and its effect on CRNS penetration depth will not only be essential for this project but also for other projects within the research unit because it is fundamental for estimating the full root zone water fluxes and water balance calculations. Resulting soil moisture profiles will be, for example, integrated into the depth scaling approaches of hydrogeodesy, will support the regionalization efforts and better constrain snow water equivalents measured by CRNS. In addition, we will define synthetic soil moisture data sets for testing CRNS interpretation, radiative transfer models and hydrogravimetry approaches at small catchment scale together with other research modules in one of the Cosmic Sense cross-cutting activities, and will be in charge for its overall organization.