Modeling the Soil-Water Retention Characteristic With Pedotransfer Functions for Shallow Seedling Recruitment

Abstract

The soil-water retention characteristic (SWRC) is a necessary parameter in seedling recruitment studies. The SWRC was investigated for three 25-mm increments of the shallow seedling recruitment zone to a depth of 75 mm at three hillslope positions on two hillslope aspects across cultivated field topography. Volumetric water content was determined at matric potentials from saturation to −1.5 MPa for the middle soil increment. Three local pedotransfer functions (PTF) were developed using basic soil physical properties and detailed particle size distribution to estimate the parameters of the van Genuchten model for the middle soil increment. The local PTF were compared with Rosetta, HYPRES, and SOILPROP regional PTF. The local PTF generally predicted water retention better than the regional PTF. Rosetta H4 and H5 models predicted water retention as well as one of the local PTF. The SWRC in the upper and lower soil increments were estimated by local PTF using soil properties from the upper and lower increments coupled with the estimated SWRC from the middle increment. Soil properties used to parameterize local PTF varied with soil depth; however, SWRC did not differ with depth. Where direct measurement of soil hydraulic properties is resource limiting, accurate estimation of local SWRC by regional PTF is possible; however, input of partial water retention information was necessary to achieve accuracy. Using local PTF to estimate the SWRC in the upper and lower profile increments of the seedling recruitment zone indicates that a single SWRC is sufficient to describe the profile in this study.