Pedotransfer functions to estimate hydraulic properties of tropical Sri Lankan soils

Knowledge of the hydraulic properties of soil is a vital factor in evaluating and managing environmental and agricultural problems. The expense and difficulty of measurements have prompted the development of other approaches to estimate soil hydraulic properties. Pedotransfer functions (PTFs) are predictive functions used to estimate soil properties on the basis of easily measurable soil parameters. Although PTFs are in use for most temperate regions, few attempts have been made to develop them for locations in the tropics. This study aimed to establish suitable PTFs for tropical soils of Sri Lanka to estimate soil hydraulic properties (field capacity and permanent wilting point) by a multiple linear regression method from inputs consisting of different combinations of four easily measured parameters: sand content; sand, silt, and clay content; bulk density; and organic carbon concentration. This analysis used the open-source data mining software in the Waikato Environment for Knowledge Analysis. We found that all the PTFs developed using different input levels showed similar performances. Our functional evaluation showed that the output of the PTFs performed essentially as well as measured data for estimating available water content and generating irrigation schedules for the selected localities. Hence, even using sand percentage alone, volumetric water contents at -10, -33, and -1500 kPa can be successfully estimated using PTFs developed for Sri Lankan soil conditions.