Combination of Measurement Methods for a Wide-Range Description of Hydraulic Soil Properties

Thomas Weninger,Gernot Bodner,Parvathy Chandrasekhar,Janis Kreiselmeier,Karl-Heinz Feger,Stefan Julich,Andreas Schwen,Kai Schwärzel

doi:10.3390/w10081021

Abstract

Established measurement methods for hydraulic soil properties cover a limited soil moisture range. Simulations of soil water dynamics based on such observations are therefore rarely representative for all conditions from saturation to drought. Recent technical developments facilitate efficient and cheap collecting of soil water characteristics data, but the quantitative benefit of extended measurement campaigns has not been adequately tested yet. In this study, a combination of four methods to measure water retention and hydraulic conductivity at different moisture ranges was applied. Evaporation method, dewpoint psychrometry, hood infiltrometer experiments, and falling head method for saturated conductivity were conducted at two experimental sites in eastern Austria. Effects of including the particular methods in the measurement strategy were examined by visual evaluation and a 1D-modelling sensitivity study including drainage, infiltration and drought conditions. The evaporation method was considered essential due to its broad measurement range both for water retention and hydraulic conductivity. In addition to that, the highest effect on simulated water balance components was induced by the inclusion of separate conductivity measurements near saturation. Water content after three days of drainage was 15 percent higher and the transpiration rate in a drought period was 22 percent higher without near-saturated conductivity measurements. Based on relative comparisons between different combinations, we suggested combining evaporation method and hood infiltrometer experiments as the basis for representative predictions of soil water dynamics.

Highlights

Numerical simulations of soil water dynamics are supposed to comprise a wide range of soil moisture conditions; matching simulation data with reality is a fundamental issue of soil science [1,2].The components which control a model’s ability to represent reality over the full moisture range are the hydraulic soil properties (HSP)
HSP are formalized in two mathematical functions: (i) the water retention function θ (h), the relation of volumetric soil water content θ and soil water head h; and (ii) the hydraulic conductivity function K (h), where K is the
Water 2018, 10, 1021 hydraulic conductivity of soil [1,3]. These functions are defined by parameters which may be derived indirectly by empirical pedotransfer functions (PTF) [4,5] or from direct measurements of θ (h) and

Summary

Introduction

The components which control a model’s ability to represent reality over the full moisture range are the hydraulic soil properties (HSP). Water 2018, 10, 1021 hydraulic conductivity of soil [1,3]. These functions are defined by parameters which may be derived indirectly by empirical pedotransfer functions (PTF) [4,5] or from direct measurements of θ (h) and K (h) [6]. In contrast to PTF, direct measurements of HSP allow for site-specific capture of soil physical characteristics with high spatial and temporal resolution. Most of the established direct measurement methods yield data only for the retention function or for a limited range of soil moisture [7,8]

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