Estimativa dos parâmetros da equação de van Genuchten em laboratório e por modelagem inversa com Hydrus-1D

Abstract

The monitoring of soil hydraulic behavior is fundamental in irrigated agriculture, because it influences crop production and environmental preservation. Thus, the soil-water characteristic curve (SWCC) gains importance, since it guides when and how much to irrigate, optimizing the use of water. The SWCC can be obtained in the field or laboratory, being commonly determined in laboratory with pressure plate extractor. Its adjustment can be made by several models, but one of the most used is the van Genuchten (1980) equation. Obtaining of soil hydraulics parameters, such as SWCC, is often difficult due to issues such as time and labor. So, pedotransfer functions, which allows to obtain soil parameters indirectly, gain utility. In this scenario is the inverse modeling, which allows a variable to be obtained through its implications, thus, it starts from the effect and arrives at the cause. The Hydrus-1D model is an example of inverse approach that allows the achievement of soil hydraulic properties. Therefore, this study was based on the hypothesis that the Hydrus-1D model, because it is based on physical processes, correctly simulates the parameters of the van Genuchten equation and, consequently, the SWRC of an Argissolo, in a way more coherent with the field conditions than those obtained in the laboratory, besides reducing the time and the labor of the procedure. Therefore, the objective of this work was to obtain, in an Argissolo, the parameters of the van Genuchten equation with Hydrus-1D inverse approach, as well as in the laboratory, and to make the respective comparisons and inferences. To do so, data of matric potential over time from an instantaneous profile experiment were collected in an Argissolo Amarelo in Fortaleza/CE. Six batteries with three tensiometers each were installed around the center of the experimental plot, at depths of 0.20, 0.35 and 0.50 m. The target depth was 0.35 m, where the root system of most cultivated species is concentrated. The other tensiometers were used to obtain the potential gradient. The Hydrus-1D model was fed with matric potential data to obtain the parameters of the van Genuchten equation. The laboratory curves were obtained in a porous plate extractor, with four replicates. The normality of the data was verified by Jarque-Bera test and the comparison of means was made by Student's t-test, both at 5% of significance. Graphs of moisture versus time and matric potential versus time were also plotted, to verify if the adjusted data matched those of the field. This verification was performed using the coefficient of efficiency – E, and the root mean squared error- RMSE. It was concluded that, generally, the Hydrus-1D model estimates the parameters of the van Genuchten equation, and consequently, the SWCC of an Argissolo in a more coherent way than the ones obtained in laboratory; and if field data are supplied, Hydrus-1D simulates well the behavior of matric potential and moisture in time, reducing the time and labor of obtaining the parameters of the van Genuchten equation in the laboratory.