Modeling hydraulic properties of sandy soils of Niger using pedotransfer functions

Abstract

Direct determination of soil hydraulic properties is often costly and laborious hence the use of indirect methods such as pedotransfer functions (PTFs). Despite progress made in PTF development in general, little evaluation of PTFs has been done for the sandy soils of Niger. We tested the ability of three PTFs, (Campbell, van Genuchten, and Vauclin) to determine soil water retention and unsaturated hydraulic conductivity ( K) for sandy soils at two villages (Banizoumbou and Bagoua) in Niger. Modeled K was compared to K estimated from neutron probe readings at 1.4 m; and modeled moisture retention was compared to lab measurements derived from the hanging water column method and pressure plate apparatus for the following depth intervals: 0–30, 30–60, and > 60 cm at Banizoumbou; and 0–30, 30–120, and > 120 cm at Bagoua. The Campbell PTF resulted in lower root mean square error (RMSE) (0.05–0.06 m 3 m − 3) for soil moisture retention for the three depth intervals at the two sites and performed better than the van Genuchten function (RMSE 0.06–0.07 m 3 m − 3) for Bagoua soils which had higher sand content. The van Genuchten PTF consistently overestimated dry regime moisture retention for the three depth intervals especially at Bagoua but performed well for the wet regime. The Campbell and Vauclin PTFs underestimated K (RMSE 0.61–1.01 mm d − 1) at both sites whereas the van Genuchten model was close to field measurements (RMSE 0.26–0.47 mm d − 1). These results show that the Campbell model is a cheaper alternative to direct measurement of moisture retention and the van Genuchten function can be used to estimate K for Niger's sandy soils with modest accuracy.