Development of pedotransfer functions for estimating water retention curve for tropical soils of the Brazilian savanna

Pedotransfer functions developed especially for predicting soil-water retention for tropical soils are very scarce and the existing ones still need improvement. The aims of this work were to create a consistent database about the physical properties of the Brazilian savanna tropical soils and to develop specific pedotransfer functions for estimating their soil-water retention characteristics. The soil database, which consisted of soil-water retention curves and related soil-physical characteristics, came from 413 locations and various depths, totalizing 1401 soil layers. Two non-linear models were proposed to estimate the four parameters of the van Genuchten equation, used to describe soil-water retention curves. The performance of the proposed models was statistically evaluated and their estimation efficiency was compared with the Tomasella's pedotransfer function considered as a reference for Brazilian soils. The soil database generated in the scope of this study is quite representative of the Brazilian savanna region. The success in predicting soil-water retention curve by using the herein developed pedotransfer functions was about 70%, which is much higher than the percentage of success obtained by Tomasella's model level 1 (20%) for the same soil database.