The authors gratefully acknowledge the financial support provided by the Canadian Foundation for Innovation (John Evans Leadership Fund) in the acquisition of the hydraulic property analyser instrument.

1. Soil sampling and sample preparation
NOTE: A schematic diagram of the workflow of this method can be found in Figure 1.
<ol>
	<li>Sample collection
	<ol>
		<li>Excavate the top few centimeters above the desired sampling depth to remove unwanted debris, particularly loose organic litter and soil surface crusting.</li>
		<li>Place the metal sampling core level on the surface of the exposed soil, with the sharp edge side facing the soil surface;...

Protocol for Soil Hydraulic Property Measurement via Evaporation

<ol>
	<li>Malaya, C., Sreedeep, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Critical+review+on+the+parameters+influencing+soil-water+characteristic+curve.">Critical review on the parameters influencing soil-water characteristic curve.</a> J Irrig Drain Eng. 138 (1), 55-62 (2011).</li><li>Schelle, H., Heise, L., J&#228;nicke, K., Durner, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Water+retention+characteristics+of+soils+over+the+whole+moisture+range:+A+comparison+of+laboratory+methods.">Water retention characteristics of soils over the whole moisture range: A comparison of laboratory methods.</a> Eur J Soil Sci. 64 (6), 814-821 (2013).</li><li>Iheshiulo, E. M. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Crop+rotations+influence+soil+hydraulic+and+physical+quality+under+no-till+on+the+Canadian+prairies.">Crop rotations influence soil hydraulic and physical quality under no-till on the Canadian prairies.</a> Agric Ecosyst Environ. 361, 108820 (2024).</li><li>Mozaffari, H., Moosavi, A. A., Sepaskhah, A., Cornelis, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Long-term+effects+of+land+use+type+and+management+on+sorptivity,+macroscopic+capillary+length+and+water-conducting+porosity+of+calcareous+soils.">Long-term effects of land use type and management on sorptivity, macroscopic capillary length and water-conducting porosity of calcareous soils.</a> Arid Land Res Manag. 36 (4), 371-397 (2022).</li><li>Rezaei, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+to+relevantly+characterize+hydraulic+properties+of+saline+and+sodic+soils+for+water+and+solute+transport+simulations.">How to relevantly characterize hydraulic properties of saline and sodic soils for water and solute transport simulations.</a> J Hydrol. 598, 125777 (2021).</li><li>Kiani, M., Hernandez-Ramirez, G., Quideau, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spatial+variation+of+soil+quality+indicators+as+a+function+of+land+use+and+topography.">Spatial variation of soil quality indicators as a function of land use and topography.</a> Can J Soil Sci. 100 (4), 463-478 (2020).</li><li>Ghezzehei, T. A., Sulman, B., Arnold, C. L., Bogie, N. A., Berhe, A. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+role+of+soil+water+retention+characteristic+on+aerobic+microbial+respiration.">On the role of soil water retention characteristic on aerobic microbial respiration.</a> BG. 16 (6), 1187-1209 (2019).</li><li>Mapa, R. B., Green, R. E., Santo, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Temporal+variability+of+soil+hydraulic+properties+with+wetting+and+drying+subsequent+to+tillage.">Temporal variability of soil hydraulic properties with wetting and drying subsequent to tillage.</a> SSSAJ. 50 (5), 1133-1138 (1986).</li><li>Parker, N., Patrignani, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Revisiting+laboratory+methods+for+measuring+soil+water+retention+curves.">Revisiting laboratory methods for measuring soil water retention curves.</a> SSSAJ. 87 (2), 417-424 (2023).</li><li>Solone, R., Bittelli, M., Tomei, F., Morari, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Errors+in+water+retention+curves+determined+with+pressure+plates:+Effects+on+the+soil+water+balance.">Errors in water retention curves determined with pressure plates: Effects on the soil water balance.</a> J Hydrol. 470, 65-74 (2012).</li><li>Cresswell, H. P., Green, T. W., McKenzie, N. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+adequacy+of+pressure+plate+apparatus+for+determining+soil+water+retention.">The adequacy of pressure plate apparatus for determining soil water retention.</a> SSSAJ. 72 (1), 41-49 (2008).</li><li>Wind, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Capillary conductivity data estimated by a simple method. , (1968).</li><li>Schindler, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ein+Schnellverfahren+zur+Messung+der+Wasser-leitf&#228;higkeit+im+teilges&#228;ttigten+Boden+an+Stechzylinderproben.Arch.">Ein Schnellverfahren zur Messung der Wasser-leitf&#228;higkeit im teilges&#228;ttigten Boden an Stechzylinderproben.Arch.</a> Acker- Pflanzenbau Bodenkd. 24, 1-7 (1980).</li><li>Peters, A., Durner, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simplified+Evaporation+Method+for+Determining+Soil+Hydraulic+Properties.">Simplified Evaporation Method for Determining Soil Hydraulic Properties.</a> J Hydrol. 356, 147-162 (2008).</li><li>Lipovetsky, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=HYPROP+measurements+of+the+unsaturated+hydraulic+properties+of+a+carbonate+rock+sample.">HYPROP measurements of the unsaturated hydraulic properties of a carbonate rock sample.</a> J Hydrol. 591, (2020).</li><li>Daly, E. J., Kim, K., Hernandez-Ramirez, G., Klimchuk, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+response+of+soil+physical+quality+parameters+to+a+perennial+grain+crop.">The response of soil physical quality parameters to a perennial grain crop.</a> Agric Ecosyst Environ. 343, 108265 (2023).</li><li>Guenette, K. G., Hernandez-Ramirez, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tracking+the+influence+of+controlled+traffic+regimes+on+field+scale+soil+variability+and+geospatial+modelling+techniques.">Tracking the influence of controlled traffic regimes on field scale soil variability and geospatial modelling techniques.</a> Geoderma. 328, 66-78 (2018).</li><li>Hebb, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Soil+physical+quality+varies+among+contrasting+land+uses+in+Northern+Prairie+regions.">Soil physical quality varies among contrasting land uses in Northern Prairie regions.</a> Agric Ecosyst Environ. 240, 14-23 (2017).</li><li>Shokrana, M. S. B., Ghane, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+of+soil+water+characteristic+curve+using+HYPROP2.">Measurement of soil water characteristic curve using HYPROP2.</a> MethodsX. 7, 100840 (2020).</li><li>Brooks, R. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Hydraulic properties of porous media. , (1965).</li><li>Kosugi, K. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lognormal+distribution+model+for+unsaturated+soil+hydraulic+properties.">Lognormal distribution model for unsaturated soil hydraulic properties.</a> Water Resour Res. 32 (9), 2697-2703 (1996).</li><li>Fredlund, D. G., Xing, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Equations+for+the+soil-water+characteristic+curve.">Equations for the soil-water characteristic curve.</a> Can Geotech J. 31 (4), 521-532 (1994).</li><li>van Genuchten, M. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+closed-form+equation+for+predicting+the+hydraulic+conductivity+of+unsaturated+soils.">A closed-form equation for predicting the hydraulic conductivity of unsaturated soils.</a> SSSAJ. 44, 892-898 (1980).</li><li>Schindler, U., Durner, W., von Unhold, G., M&#252;ller, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaporation+method+for+measuring+unsaturated+hydraulic+properties+of+soils:+Extending+the+measurement+range.">Evaporation method for measuring unsaturated hydraulic properties of soils: Extending the measurement range.</a> SSSAJ. 74 (4), 1071-1083 (2010).</li><li>Bagnall, D. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Selecting+soil+hydraulic+properties+as+indicators+of+soil+health:+Measurement+response+to+management+and+site+characteristics.">Selecting soil hydraulic properties as indicators of soil health: Measurement response to management and site characteristics.</a> SSSAJ. 86 (5), 1206-1226 (2022).</li></ol>

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...

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 (&#952;) 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, amendments, agroecosystem types, and environmental conditions can all have an impact on soil hydraulics3,4. These factors can in turn influence solute transport5 and plant available water6, soil respiration and microbial activity7, as well as wetting and drying cycles8. As an important piece in quantifying healthy and functioning soil, proper analysis of the SWRC is imperative for obtaining an informed understanding of soil hydraulic properties.
A variety of measurement techniques currently exist for developing a reliable SWRC, with the hanging-water column and pressure plate methods being common traditional approaches for determining the pore size distribution of soil2. Traditional methods can be time-consuming, usually taking weeks or months to analyze a small set of samples9. Moreover, once analysis is complete, these methods result in only a few data points that inform the SWRC9. Additionally, the accuracy of producing representative data using traditional methods such as pressure plates can become a concern at lower matric potentials, in particular, with fine-textured soils10,11. More modern techniques, which involve the simple evaporation experiment approach using tensiometers and the chilled-mirror dew point method, tend to deliver more reproducible data across a wide range of soil textures2. Initially developed by Wind in 1968, the simple evaporation experiment involved measuring water mass changes and tension changes through tensiometers in the soil sample over time12. As evaporation occurs, soil sample mass measurements are taken at specific time intervals to create an SWRC. Later refined by Schindler (1980), the method involved only two tensiometers placed at different pressure heads within the soil sample. The modified method was then tested and validated as capable of being used in scientific analysis13,14. A key benefit of the simple evaporation experiment is the potential to easily produce data across a large portion of the soil moisture curve (0 to -300 kPa), with more data points than with traditional methods. 
These modern methods involve automated instruments that take numerous data points throughout the sample analysis period and produce data using a software interface. The hydraulic property instrument is a contemporary instrument that creates water retention curves and conductivity curves from sample data15. By employing a simple evaporation experiment using the hydraulic property instrument, the relationship between water content and water potential in the soil can be evaluated1. In this experiment, water present within the tensiometer shaft exists in an equilibrium with water in the soil solution. As evaporation of soil water occurs and the soil sample dries, cavitation takes place in the tensiometer, and the experiment ends. There is a limitation of the hydraulic property instrument in the dry range of the SWRC, as the instrument is only capable of operating within matric potentials of 0 to -100 kPa. This can be remedied with the inclusion of data generated with a chilled-mirror dew point experiment using a soil water potential instrument16, which can extend the data range to -300,000 kPa or the permanent wilting point. All these data are brought together in the modeling software post processing to cohesively inform the SWRC from null tensions to higher tensions even beyond wilting point. The SWRC and hydraulic conductivity curves are then generated based on matric potential data points taken throughout the measurement period, allowing a complete curve projected from saturation to permanent wilting point to be generated. 
The method described here presents a succinct operating procedure for soil analysis with a hydraulic property instrument. This method has been conducted in a number of scientific settings, including quantification of soil health in a broad range of agroecosystems3,17,18,19, and efforts have been made to understand best practices beyond the instrument user manual20. Here, a standardized protocol is outlined for all steps of the procedure, including field sampling, sample preparation, software function, and data processing. Following this method will ensure a successful campaign that results in reliable data. Critical steps for ensuring quality data, common challenges, and best practices are presented to ensure proper implementation.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>4 L Buchner Flasks (two)</td>
			<td>Various</td>
			<td>n/a</td>
			<td>Containers for water degassing</td>
		</tr>
		<tr>
			<td>20 mL Syringe, fine tip</td>
			<td>BD</td>
			<td>BD-302830</td>
			<td></td>
		</tr>
		<tr>
			<td>Coffee filter</td>
			<td>Various</td>
			<td>n/a</td>
			<td>Prevents soil travel out of core while soaking</td>
		</tr>
		<tr>
			<td>HYPROP Complete Set</td>
			<td>Hoskin</td>
			<td>110813/E240-M020210</td>
			<td>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</td>
		</tr>
		<tr>
			<td>HYPROP Refill Unit</td>
			<td>Hoskin</td>
			<td>108899/ E240-M020258</td>
			<td>vacuum pump, vacuum mount, beaker mount, refilling adapters</td>
		</tr>
		<tr>
			<td>Large Plastic Tubs</td>
			<td>Various</td>
			<td>n/a</td>
			<td>Holds water and soil cores during saturation</td>
		</tr>
		<tr>
			<td>METER hammering holder</td>
			<td>Hoskin</td>
			<td>100255/E240-100201</td>
			<td></td>
		</tr>
		<tr>
			<td>Rubber Mallet</td>
			<td>Home Depot</td>
			<td>18CT1031</td>
			<td>Sample collection tool used with hammering holder</td>
		</tr>
		<tr>
			<td>Shovel</td>
			<td>Home Depot</td>
			<td>83200</td>
			<td></td>
		</tr>
		<tr>
			<td>Soil Sampling Ring incl. 2 caps</td>
			<td>Hoskin</td>
			<td>100254/E240-100101</td>
			<td></td>
		</tr>
		<tr>
			<td>Stir plate/ Stirring Bar</td>
			<td>Various</td>
			<td>n/a</td>
			<td></td>
		</tr>
		<tr>
			<td>Trowel</td>
			<td>Home Depot</td>
			<td>91365</td>
			<td></td>
		</tr>
	</tbody>
</table>

measurements of soil water potential and conductivity based on a simple evaporation experiment using a hydraulic property analyzer

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.

Author Spotlight: Advancing Agricultural Land Ecosystem Research with a Hydraulic Property Analyzer to Assess Soil Health

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

At the Sustainable Land Ecosystems Lab, our research focuses on finding sustainable solutions to problems affecting land ecosystems, including croplands and grasslands. Solving this complex problem involves researching soil health, a key part of all agricultural land ecosystems. Obtaining a soil water retention curve that extends into the Dry Range is a challenge.Currently, it is necessary to combine the data from this experiment with additional data on another instrument. This can be less than ideal for some research objectives. The main advantage here is the amount of data the instrument can produce with relatively low user time and input.Compared to other techniques that attempt to create a soil water retention curve with few data points, this instrument provides more precise data.

Upon completing a proper measurement campaign following the protocol above, it will be possible to view the data output of the experiment in the analysis software. Output curves originate from tensiometer readings that measure water tension (hPa) over time (t), and the initial curve of this data is generated immediately after termination of the campaign. Selected examples of tension curves of two soil samples can be examined to illustrate optimal and suboptimal results (Figure 2). Optimal re...

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.

The measurement of soil hydraulic properties is critical in understanding the physical components of soil health as well as integrated knowledge of soil ...

measurements-soil-water-potential-conductivity-based-on-simple

Research

JoVE Journal

Environment

163 Views.  University of Alberta. At the Sustainable Land Ecosystems Lab, our research focuses on finding sustainable solutions to problems affecting land ecosystems, including croplands and grasslands. Solving this complex problem involves researching soil health, a key part of all agricultural land ecosystems. Obtaining a soil water retention curve that extends into the Dry Range is a challenge.Currently, it is necessary to combine the data from this experiment with additional data on another instrument. This can be ...