Abstract
Detailed knowledge on water percolation into the soil in irrigated areas is fundamental for solving problems of drainage, pollution and the recharge of underground aquifers. The aim of this study was to evaluate the percolation estimated by time-domain-reflectometry (TDR) in a drainage lysimeter. We used Darcy's law with K(θ) functions determined by field and laboratory methods and by the change in water storage in the soil profile at 16 points of moisture measurement at different time intervals. A sandy clay soil was saturated and covered with plastic sheet to prevent evaporation and an internal drainage trial in a drainage lysimeter was installed. The relationship between the observed and estimated percolation values was evaluated by linear regression analysis. The results suggest that percolation in the field or laboratory can be estimated based on continuous monitoring with TDR, and at short time intervals, of the variations in soil water storage. The precision and accuracy of this approach are similar to those of the lysimeter and it has advantages over the other evaluated methods, of which the most relevant are the possibility of estimating percolation in short time intervals and exemption from the predetermination of soil hydraulic properties such as water retention and hydraulic conductivity. The estimates obtained by the Darcy-Buckingham equation for percolation levels using function K(θ) predicted by the method of Hillel et al. (1972) provided compatible water percolation estimates with those obtained in the lysimeter at time intervals greater than 1 h. The methods of Libardi et al. (1980), Sisson et al. (1980) and van Genuchten (1980) underestimated water percolation.
Highlights
Knowledge of the patterns of water movement in the soil is essential to solve problems involving irrigation, drainage, water conservation, aquifer recharge and pollution, as well as infiltration and control of runoff (Hillel et al, 1972)
The method proposed by Hillel et al (1972) allows the calculation of K(θ) in the field in a process of internal drainage when there is no flow on the soil surface
Other methods are indirect, allowing a theoretical calculation of the function K(θ) from water retention data in the soil obtained in the laboratory
Summary
Knowledge of the patterns of water movement in the soil is essential to solve problems involving irrigation, drainage, water conservation, aquifer recharge and pollution, as well as infiltration and control of runoff (Hillel et al, 1972). Other methods are indirect, allowing a theoretical calculation of the function K(θ) from water retention data in the soil obtained in the laboratory (van Genuchten, 1980; Weynants et al, 2009). Both the direct and indirect methods are time-intensive, generate costs due to the need for pre-determinations of hydraulic properties, are error-prone, and the results are only valid on a local scale (Mermoud & Xu, 2006; Arya & Heitman, 2010)
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