Abstract
The soil hydraulic parameters for analyzing soil water movement can be determined by fitting a soil water retention curve to a certain function, i.e., a soil hydraulic model. For this purpose, a program which performs nonlinear fitting of soil water retention curves to 4 models, Brooks and Corey model, van Genuchten model, Kosugfs lognormal pore-size distribution model, and Durnefs bimodal pore-size distribution model, by Levenberg-Marquardt method was developed. The program was written in GNU Octave, a high-level language primarily intended for numeric calculation. It was shown that the developed program actually works fine with many soil water retention curves in UNSODA database. It was also shown that by comparing coefficients of determination and fitting curves of each model, the most appropriate hydraulic model for a certain soil can be selected. Therefore this program not only calculates the necessary parameters, but also helps determining which model is to be used for a particular purpose.
