Modeling water fluxes through containerized soilless substrates using HYDRUS

Authors: FIELDS, J - Louisiana State University; Owen Jr, James - Jim; STEWART, R - Virginia Polytechnic Institution & State University; HEITMAN, J - North Carolina State University; CARON, J - Laval University

Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2020
Publication Date: 5/30/2020
Citation: Fields, J.S., Owen Jr, J.S., Stewart, R.D., Heitman, J.L., Caron, J. 2020. Modeling water fluxes through containerized soilless substrates using HYDRUS. Vadose Zone Journal. 19(1):e20031. https://doi.org/10.1002/vzj2.20031.
DOI: https://doi.org/10.1002/vzj2.20031

Interpretive Summary: Containerized crop production can enhance plant health and ensure environmental sustainability, yet proper management requires we understand how water moves and is stored within growing media. Models that simulate water storage and movement have remain underutilized in horticultural crops. Therefore, our goal was assess the accuracy of models with two growing media used in greenhouses or nurseries; determine what is most important model inputs and outputs; and compare the model to three laboratory methods. The model provided accurate simulations of water flux through growing media when properly calibrated. Results showed the water content was the most important model input. Hydrologic models of growing media used in horticultural crop production may allow growers to better schedule irrigation or avoid excess drainage. These models can also serve to analyze potential new substrates prior to conducting growth evaluations compared to current substrate assessment techniques that can be costly in terms of time and materials.

Technical Abstract: Containerized crop production can enhance plant health and ensure environmental sustainability, yet proper management requires improved understanding of water fluxes and storage within soilless substrates. Numerical simulation tools developed to simulate water movement in porous media, such as HYDRUS-3D, may help to quantify effective hydraulic properties of soilless substrates, but have not yet been tested in this capacity. Therefore, this study had three main objectives: 1) assess the accuracy of HYDRUS-3D for simulating water flow through peat- and bark-based soilless substrates by comparing measured and modeled drainage and water storage; 2) determine sensitivity of model outputs to individual hydraulic parameters; and 3) compare model parameterization using three laboratory characterization methods (instantaneous profile sorption, instantaneous profile desorption, evaporation) versus inverse modeling with HYDRUS. The results showed that the modeled water contents and drainage timing and amounts were most sensitive to saturated volumetric water content ('s) and least sensitive to saturated hydraulic conductivity (Ks). With regard to parameterization methods, the inverse modeling approach provided the most accurate water balance simulations for both substrates, followed by the sorption method. These two methods estimated lower peak water contents and greater drainage compared to simulations parameterized using desorption and evaporation measurements. Overall, the study results showed that the Richards equation, as calculated using HYDRUS, can provide accurate simulations of water flux through containers when properly calibrated, though sorption-derived parameters may suffice when model optimization is impractical.