Measurements of Soil Water Potential and Conductivity based on a Simple Evaporation Experiment using a Hydraulic Property Analyzer

Summary

This article features a simple evaporation experiment using a hydraulic property instrument for a soil sample. Through efficient means, measurements can be taken over a series of days to generate high-quality data.

Abstract

The measurement of soil hydraulic properties is critical in understanding the physical components of soil health as well as integrated knowledge of soil systems under various management practices. Collecting reliable data is imperative for informing decisions that affect agriculture and the environment. The simple evaporation experiment described here uses instrumentation in a laboratory setting to analyze soil samples collected in the field. The soil water tension of the sample is measured by the instrument, and tension data is modeled by software to return soil hydraulic properties. This method can be utilized to measure soil water retention and hydraulic conductivity and give insight into differences in treatments or environmental dynamics over time. Initial establishment requires a user, but data acquisition is automated with the instrument. Soil hydraulic properties are not easily measured with traditional experiments, and this protocol offers a simple and optimal alternative. Interpretation of results and options for extending the data range are discussed.

Introduction

Soil water retention and hydraulic conductivity within natural and human-altered environments help us understand and observe changes in soil health and functionality. Quantifying hydraulic properties through the soil water retention curve (SWRC) and soil water conductivity curve offers insight into key drivers of soil physical behavior and water movement characterization¹. The relationship between volumetric water content (θ) and matric head (h) is represented within an SWRC, and the ranges within the curve describe the saturation point, field capacity, and permanent wilting point². Soil management practices, amendm....

Protocol

1. Soil sampling and sample preparation

NOTE: A schematic diagram of the workflow of this method can be found in Figure 1.

1. Sample collection
   1. Excavate the top few centimeters above the desired sampling depth to remove unwanted debris, particularly loose organic litter and soil surface crusting.
   2. Place the metal sampling core level on the surface of the exposed soil, with the sharp edge side facing the soil surface;.......

Discussion

The simple evaporation experiment approach using the method that is described here is an efficient means to develop the SWRC and hydraulic conductivity curves. Simplicity and accuracy of data measurement make it a viable alternative to more traditional methods¹⁴. The method described here goes beyond the user manual and current literature to synthesize and expand on finer points of this intricate instrument. Particular attention needs to be paid to the soil sample collection, transport, and analys.......

Materials

Name	Company	Catalog Number	Comments
4 L Buchner Flasks (two)	Various	n/a	Containers for water degassing
20 mL Syringe, fine tip	BD	BD-302830
Coffee filter	Various	n/a	Prevents soil travel out of core while soaking
HYPROP Complete Set	Hoskin	110813/E240-M020210	tensiometer shaft auger, tube for vacuum syringe and refilling adapter, auger guide, HYPROP USB adapter, HYPROP sensor unit, tensiometer shafts (50 mm and 25 mm), saturation plate, refilling adapter, silicone gasket, set of o-rings, LABROS balance, software, cables
HYPROP Refill Unit	Hoskin	108899/ E240-M020258	vacuum pump, vacuum mount, beaker mount, refilling adapters
Large Plastic Tubs	Various	n/a	Holds water and soil cores during saturation
METER hammering holder	Hoskin	100255/E240-100201
Rubber Mallet	Home Depot	18CT1031	Sample collection tool used with hammering holder
Shovel	Home Depot	83200
Soil Sampling Ring incl. 2 caps	Hoskin	100254/E240-100101
Stir plate/ Stirring Bar	Various	n/a
Trowel	Home Depot	91365