Determination of the Soil Water Retention Curve around the Wilting Point: Optimized Protocol for the Dewpoint Method

Abstract

Soil water retention curve over the entire moisture range with high accuracy. Combination of evaporation method and dewpoint method. No a priori knowledge on soil texture needed. Experimental methodology that is reliable, efficient, and easy to use. Accurate knowledge of the soil water retention curve (WRC) is essential for various hydrological and plant‐physiological studies. Currently, there is a lack of a uniform protocol for measuring the wilting point water content (WP) with the dewpoint method (DP), despite its ecological relevance and frequent use to calculate available water capacity. We present a new protocol for measuring the WP with the dewpoint method. In contrast to existing methods which add or remove specific amounts of water to moist, air‐dry, or oven‐dry soil, we propose to apply the dewpoint method after the evaporation method in which tensiometers measure the pressure head of the soil. We suggest to stop the evaporation experiment when the air‐entry of one tensiometer cup is reached, to slice the soil core into slabs, and to apply the dewpoint method to subsamples of the slabs. We test the method by numerical simulations and laboratory experiments on five soils covering a broad range of texture. We investigate the accuracy, robustness, and practicability of the new method and compare it to the existing protocols for the dewpoint method and the pressure plate technique. We find that the proposed method allows a precise determination of the WP and the WRC across the full moisture range. It is easy to perform, robust, accurate, and does not require any a priori guess about the amount of water to be added or removed. By fitting a retention curve to the measured data, any water content, including the WP, can be obtained with great confidence.

Modeling near‐surface water redistribution in a desert soil

“…The WP4C combined with an analytical balance (Mettler Toledo MS 104 TS) was used to measure water potentials and the corresponding water contents of the soil at the dry end of the water retention curve (pF 3.3 to pF 6.3). Following the protocol developed by Kirste, Iden, and Durner (2019), we were able to obtain a water retention curve for Lysimeter 1 soil ranging from pF 0 to pF 6.3, which covers the suction heads from water‐saturated to air‐dry soil conditions. The unsaturated hydraulic conductivity ranging from pF 2 to pF 3 was also determined from the HYPROP evaporation measurements (Schindler, Durner, von Unold, & Müller, 2010).…”

Capillary, Film, and Vapor Flow in Transient Bare Soil Evaporation (2): Experimental Identification of Hydraulic Conductivity in the Medium to Dry Moisture Range

“…oven-dryness (Schelle et al, 2013;Kirste et al, 2019). Despite this progress, there is still a lack of measurements of the HCC in the data range not supported by tensiometers.…”

Field Monitoring and Laboratory Testing for an Integrated Modeling of River Embankments under Transient Conditions

“…Extensive laboratory measurements were performed on samples having initial void ratios e0 varying in the range 0.48 -0.86, as reported in the figures. A combination of the evaporation method, from high to intermediate values of saturation (Schindler et al, 2012), and of the chilled mirror method, towards the dry region of the SWRC (Kriste et al, 2019) has been used to determine main drying curves. Extended evaporation methods were also used for additional information on intermediate to low values of saturation (Schindler et al, 2010;Schelle et al, 2013).…”