Estimating the unimodal and bimodal van Genuchten model parameters using the simplified evaporation and dewpoint methods

Abstract

<p>The pressure plate method has been widely used for describing the soil water retention curve (SWRC). However, the simplified evaporation method (SEM) appears as an alternative because of its high resolution and automatization. On the other hand, the unimodal and bimodal van Genuchten models (VGM) have been used for describing the SWRC by computing the shape parameters. However, parametric pedotransfer functions (PTFs) have been developed based on the pressure plates method, focusing on the unimodal VGM. Therefore, the objectives of this study were: (1) to measure the SWRC with the simplified evaporation method (SEM) coupled to the dewpoint potentiometer (DP) in soils with different land use and soil texture, (2) to adjust and compare the VG unimodal and bimodal parameters, and (3) to estimate the VG unimodal and bimodal parameters through regression techniques including a linear approach and random forest. Thirty topsoils (disturbed and undisturbed cores) were sampled across a climate gradient and measured by duplicated. Preliminary results showed that the high resolution of the SWRC data obtained with the SEM + DP leads to a better fit when using the bimodal VGM.</p>

How does building healthy soils impact sustainable use of water resources in irrigated agriculture?

“…For instance, while LPJmL, Aqua-Crop, and SWAT use total porosity as an input of a unimodal pore size distribution, HYDRUS 1D accounts for dualporosity, that is, interaggregate pores and intra-aggregate pores with contrasting sizes and hysteresis in the water flow calculation (S ˇimu ˚nek et al, 2016). Not considering bimodality in topsoils due to soil management derived from tillage may compromise the accuracy of soil-water modeling (Jensen et al, 2019;Acevedo et al, 2020). A HYDRUS 1D module can incorporate the effect of tillage, homogenizing the soil water content and liquid phase concentration in the topsoil layers, although it does not incorporate changes in soil hydraulic properties with tillage (Mallmann et al, 2014).…”