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There are hundreds of soil tests that can be conducted, both in the field or laboratory. This page provides an overview of more common soil tests, links to information on sampling, and links to test methods.
 
There are hundreds of soil tests that can be conducted, both in the field or laboratory. This page provides an overview of more common soil tests, links to information on sampling, and links to test methods.
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==Sample collection==
 
==Sample collection==
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[[file:Direct push technology.jpg|300px|thumb|alt=image of sampling rig|<font size=3>Example of direct push technology used to collect a soil sample.</font size>]]
 +
 
Soil sample collection methods vary and covering all acceptable methods is beyond the scope of this page. Below are links to sampling methods, including videos.
 
Soil sample collection methods vary and covering all acceptable methods is beyond the scope of this page. Below are links to sampling methods, including videos.
 
===Sampling for chemical tests===
 
Note that these references provide information on soil sample collection. Except where noted, they do not include field procedures associated with specific tests and most do not include information on quality assurance and quality control (QA/QC). Use professional, certified/licensed individuals or firms to ensure appropriate QA/QC procedures are followed.
 
  
 
'''Documents'''
 
'''Documents'''
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==Chemical tests==
 
==Chemical tests==
 +
Most chemical tests are conducted in the laboratory on samples collected in the field.
  
===Laboratory tests===
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===Recommended holding times and preservation===
Below is a list of recommended laboratory tests.
 
 
 
====Recommended holding times and preservation====
 
 
*[https://alphalab.com/index.php/air-testing/4-supportservicessection/supportservicescategory/32-holding-times]
 
*[https://alphalab.com/index.php/air-testing/4-supportservicessection/supportservicescategory/32-holding-times]
 
*[https://www.eurofinsus.com/media/447768/appendix-d-section-5-attachment-holdtime-container-list_2016-july.pdf]
 
*[https://www.eurofinsus.com/media/447768/appendix-d-section-5-attachment-holdtime-container-list_2016-july.pdf]
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*[https://www.assetlaboratories.com/assets/holding-time-and-preservation.pdf]
 
*[https://www.assetlaboratories.com/assets/holding-time-and-preservation.pdf]
  
====Nutrients====
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===Nutrients===
 +
For more information [https://stormwater.pca.state.mn.us/index.php?title=Soil_chemical_properties_and_processes#Soil_chemical_properties link here].
 +
 
 
Soil macronutrients include phosphorus, nitrogen, potassium, sulfur, calcium, and magnesium. [https://stormwater.pca.state.mn.us/index.php?title=Phosphorus Phosphorus] is an important pollutant of concern in surface water, particularly lakes. Though there are several forms of phosphorus, they can roughly be divided into <span title="Dissolved phosphorus is the phosphorus that remains in water after that water has been filtered to remove particulate matter."> '''dissolved phosphorus'''</span> (includes orthophosphate and soluble phosphorus) and <span title="Phosphorus attached to solids (mineral and organic)"> '''particulate phosphorus'''</span>, with dissolved phosphorus being much more <span title="The proportion of a nutrient that is digested, absorbed and metabolized by an organism through normal pathways."> '''bioavailable'''</span> than particulate forms. Dissolved phosphorus is typically identified as phosphorus passing through a 0.45 micron filter. For a detailed discussion of phosphorus, [https://stormwater.pca.state.mn.us/index.php?title=Phosphorus_in_stormwater link here].
 
Soil macronutrients include phosphorus, nitrogen, potassium, sulfur, calcium, and magnesium. [https://stormwater.pca.state.mn.us/index.php?title=Phosphorus Phosphorus] is an important pollutant of concern in surface water, particularly lakes. Though there are several forms of phosphorus, they can roughly be divided into <span title="Dissolved phosphorus is the phosphorus that remains in water after that water has been filtered to remove particulate matter."> '''dissolved phosphorus'''</span> (includes orthophosphate and soluble phosphorus) and <span title="Phosphorus attached to solids (mineral and organic)"> '''particulate phosphorus'''</span>, with dissolved phosphorus being much more <span title="The proportion of a nutrient that is digested, absorbed and metabolized by an organism through normal pathways."> '''bioavailable'''</span> than particulate forms. Dissolved phosphorus is typically identified as phosphorus passing through a 0.45 micron filter. For a detailed discussion of phosphorus, [https://stormwater.pca.state.mn.us/index.php?title=Phosphorus_in_stormwater link here].
  
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**[https://en.wikipedia.org/wiki/Atomic_absorption_spectroscopy Atomic absorption spectroscopy]
 
**[https://en.wikipedia.org/wiki/Atomic_absorption_spectroscopy Atomic absorption spectroscopy]
  
====Metals====
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===[https://stormwater.pca.state.mn.us/index.php?title=Soil_chemical_properties_and_processes#Trace_metals Metals]===
The primary sources of metals in stormwater runoff are associated with automobiles, both from fluids and wear of parts, including tires. Concentrations of metals in stormwater runoff are generally below aquatic life and drinking water criteria, though concentrations may exceed criteria for sensitive species and in specific land uses, such as high traffic transportation areas. Metals of potential concern include copper, zinc, nickel, cadmium, and lead.
+
The primary sources of metals in stormwater runoff are associated with automobiles, both from fluids and wear of parts, including tires. Concentrations of metals in stormwater runoff are generally below aquatic life and drinking water criteria, though concentrations may exceed criteria for sensitive species and in specific land uses, such as high traffic transportation areas. Metals of greatest concern include copper, zinc, nickel, cadmium, and lead.
  
 
Samples are typically collected for total metals, meaning samples are not filtered. For dissolved metal concentrations, samples are filtered using a 0.45 micron filter. From an environmental perspective, dissolved metal concentrations more accurately reflect potential risk to receptors, since most metal bound to particles is retained in stormwater bmps. Lab methods include the following.
 
Samples are typically collected for total metals, meaning samples are not filtered. For dissolved metal concentrations, samples are filtered using a 0.45 micron filter. From an environmental perspective, dissolved metal concentrations more accurately reflect potential risk to receptors, since most metal bound to particles is retained in stormwater bmps. Lab methods include the following.
 
*[https://anlab.ucdavis.edu/analysis/Soils/390 Inductively Coupled Plasma Emission Spectrometry (ICP-AES)] - recommended due to lower detection limits, but more expensive
 
*[https://anlab.ucdavis.edu/analysis/Soils/390 Inductively Coupled Plasma Emission Spectrometry (ICP-AES)] - recommended due to lower detection limits, but more expensive
*[https://en.wikipedia.org/wiki/Atomic_absorption_spectroscopy atomic absorption spectroscopy]
+
*[https://en.wikipedia.org/wiki/Atomic_absorption_spectroscopy Atomic absorption spectroscopy]
  
====pH====
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===[https://stormwater.pca.state.mn.us/index.php?title=Soil_chemical_properties_and_processes#pH pH]===
 
Soil pH typically ranges from 6 to 8. Soils with elevated organic matter concentrations may have lower pH. Soil pH affects biologic activity and chemical reactions, particularly of some metals. Soil pH is generally not a concern, though some amendments, such as lime (increases pH), may lead to soil pH values that adversely affect soil biology, vegetation, mobilize metals, or bind up nutrients. Recommended lab methods include the following.
 
Soil pH typically ranges from 6 to 8. Soils with elevated organic matter concentrations may have lower pH. Soil pH affects biologic activity and chemical reactions, particularly of some metals. Soil pH is generally not a concern, though some amendments, such as lime (increases pH), may lead to soil pH values that adversely affect soil biology, vegetation, mobilize metals, or bind up nutrients. Recommended lab methods include the following.
 
*[https://anlab.ucdavis.edu/analysis/Soils/205 Saturated paste] - recommended
 
*[https://anlab.ucdavis.edu/analysis/Soils/205 Saturated paste] - recommended
 
*[https://www.epa.gov/sites/production/files/2015-12/documents/9045d.pdf 1:1 and 2:1 water ratios]
 
*[https://www.epa.gov/sites/production/files/2015-12/documents/9045d.pdf 1:1 and 2:1 water ratios]
  
====Organic matter and carbon====
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===[https://stormwater.pca.state.mn.us/index.php?title=Soil_chemical_properties_and_processes#Organic_matter_.28carbon.29 Organic matter and carbon]===
 +
By itself, organic matter is not generally a pollutant of concern unless it contains bound pollutants at levels of concern (e.g. metals, organic pollutants such as oil and pesticides). Organic matter can create oxygen demand in receiving waters and, as mentioned above, transport attached chemicals that may become a concern in receiving waters, including nutrients, metals , and organic pollutants. Organic matter also provides a food source for bacteria and pathogens.
 
*[https://anlab.ucdavis.edu/analysis/Soils/322 organic carbon combustion]
 
*[https://anlab.ucdavis.edu/analysis/Soils/322 organic carbon combustion]
 
*[https://anlab.ucdavis.edu/analysis/Soils/410 organic matter Walkley-Black]
 
*[https://anlab.ucdavis.edu/analysis/Soils/410 organic matter Walkley-Black]
 
*[https://anlab.ucdavis.edu/analysis/Soils/415 Organic matter loss on ignition] - recommended due to ease of use and since organic matter is more commonly used compared to organic carbon
 
*[https://anlab.ucdavis.edu/analysis/Soils/415 Organic matter loss on ignition] - recommended due to ease of use and since organic matter is more commonly used compared to organic carbon
  
====Exchange capacity====
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===[https://stormwater.pca.state.mn.us/index.php?title=Soil_chemical_properties_and_processes#Cation_exchange_capacity Exchange capacity]===
 +
Exchange capacity affects the fate of other soil chemicals, including nutrients and pollutants, and provides a buffer against soil acidification.
 
*Cation exchange capacity - multiple methods are available for cation exchange capacity. For more information [https://s3.amazonaws.com/udextension/lawngarden/files/2012/10/CHAP9.pdf read here].
 
*Cation exchange capacity - multiple methods are available for cation exchange capacity. For more information [https://s3.amazonaws.com/udextension/lawngarden/files/2012/10/CHAP9.pdf read here].
 
**[https://anlab.ucdavis.edu/analysis/Soils/430 Barium chloride Compulsive Exchange Method] - recommended but is time consuming and generates a hazardous waste
 
**[https://anlab.ucdavis.edu/analysis/Soils/430 Barium chloride Compulsive Exchange Method] - recommended but is time consuming and generates a hazardous waste
**Ammonium Acetate Method - acceptable if soil pH is near 7.0
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**[https://www.epa.gov/sites/default/files/2015-12/documents/9080.pdf Ammonium Acetate Method] - acceptable if soil pH is near 7.0
 
**Agronomic Soil Tests - estimates CEC from test extractable Ca, K, and Mg and some rapid measure of exchangeable acidity (see next bullet)
 
**Agronomic Soil Tests - estimates CEC from test extractable Ca, K, and Mg and some rapid measure of exchangeable acidity (see next bullet)
 
*[https://anlab.ucdavis.edu/analysis/Soils/360 Exchangeable Potassium, Calcium, Magnesium, Sodium And Estimated Cation Exchange Capacity]
 
*[https://anlab.ucdavis.edu/analysis/Soils/360 Exchangeable Potassium, Calcium, Magnesium, Sodium And Estimated Cation Exchange Capacity]
  
====Enzyme activity====
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===[https://stormwater.pca.state.mn.us/index.php?title=Soil_chemical_properties_and_processes#Enzymes Enzyme activity]===
 +
Enzymes in soil mediate numerous chemical reactions involved in soil nutrient cycling, transformation of plant and microbial debris, mineralization and transformation of organic matter within the carbon cycle, and transformation and degradation of potentially hazardous pollutants.
 
*Fluorescence assays - synthetic C-, N-, or P-rich substrates bound with a fluorescent dye are added to soil samples. When intact, the labeled substrates do not fluoresce. Enzyme activity is measured as the increase in fluorescence as the fluorescent dyes are cleaved from their substrates, which allows them to fluoresce. Enzyme measurements can be expressed in units of molarity or activity. See [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3991303/ this article and associated video] for a description of the method.
 
*Fluorescence assays - synthetic C-, N-, or P-rich substrates bound with a fluorescent dye are added to soil samples. When intact, the labeled substrates do not fluoresce. Enzyme activity is measured as the increase in fluorescence as the fluorescent dyes are cleaved from their substrates, which allows them to fluoresce. Enzyme measurements can be expressed in units of molarity or activity. See [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3991303/ this article and associated video] for a description of the method.
 
*Spectrophotometric assays - the course of the enzymatic reaction is followed by measuring a change in how much light the assay solution absorbs
 
*Spectrophotometric assays - the course of the enzymatic reaction is followed by measuring a change in how much light the assay solution absorbs
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===Field methods===
 
===Field methods===
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Field methods for soil chemical testing are generally not recommended, though they can be useful in providing general information. Typically field tests involve the use of test strips or probes. Portable laboratories can be used to conduct some of the analyses described above. Although these tests are conducted in the field, they utilize laboratory methods and are therefore more appropriately considered lab tests.
 +
 +
Here are some links to information on soil chemical field tests.
 +
*[https://solvita.com/fieldtest/ Soil respiration] (Solvita test)
 +
*[https://iuss.org/19th%20WCSS/Symposium/pdf/1101.pdf An automated system for rapid in-field soil nutrient testing]
 +
*Gardening centers typically provide information on field tests (e.g. for home gardens), with nutrients being the primary focus
 +
**[https://homeguides.sfgate.com/test-soil-ph-ph-test-strips-39951.html How to Test Soil PH With PH Test Strips]
 +
**[https://extension.unh.edu/blog/2020/04/are-garden-soil-test-kits-good-alternative-lab-testing Are garden soil test kits a good alternative to lab testing?]
 +
**[https://www.bobvila.com/articles/best-soil-test-kits/ The Best Soil Test Kits Tested in 2023]
 +
**[https://blog.bluelab.com/pros-and-cons-of-ph-testing-strips-for-growing The pros and cons of using pH testing strips for growing]
  
==Tests for soil physical properties==
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==Tests for soil physical and hydrologic properties==
 +
Most soil physical and hydrologic tests can be done in the field, but some require additional procedures performed in the laboratory.
  
Most soil physical soil tests can be done in the field, but some require additional procedures performed in the laboratory.
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===[https://stormwater.pca.state.mn.us/index.php?title=Soil_hydrologic_properties_and_processes#Soil_water_and_water_retention Soil water (moisture) content]===
 +
[[File:Tensiometer.jpg|300px|thumb|alt=photo of soil tensiometer|<font size=3>Example of a tensiometer's vacuum gauge. Credit: Tina Dispenza, [https://edis.ifas.ufl.edu/publication/TR015 University of Florida/IFAS]</font size>]]
  
===Soil water (moisture) content===
 
 
Laboratory analysis of soil water content is recommended for point-in-time measurements. Lab methods involve weighing a soil sample prior to drying, then drying to constant weight in oven at temperature between 100–110<sup>o</sup>C (105<sup>o</sup>C is typical). The difference in weight represents the mass of water in the sample. The water content is then expressed on a mass basis (g of water to g of dry soil), or if the bulk density is known, the volume of water to volume of soil. It is important that samples collected in the field be properly stored to avoid water loss prior to analysis. For further reading see [https://nature.berkeley.edu/soilmicro/methods/Soil%20moisture%20content.pdf].
 
Laboratory analysis of soil water content is recommended for point-in-time measurements. Lab methods involve weighing a soil sample prior to drying, then drying to constant weight in oven at temperature between 100–110<sup>o</sup>C (105<sup>o</sup>C is typical). The difference in weight represents the mass of water in the sample. The water content is then expressed on a mass basis (g of water to g of dry soil), or if the bulk density is known, the volume of water to volume of soil. It is important that samples collected in the field be properly stored to avoid water loss prior to analysis. For further reading see [https://nature.berkeley.edu/soilmicro/methods/Soil%20moisture%20content.pdf].
  
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**[https://www.youtube.com/watch?v=vVDh60WGmik Video Time Domain Reflectometry]
 
**[https://www.youtube.com/watch?v=vVDh60WGmik Video Time Domain Reflectometry]
 
**[https://media.neliti.com/media/publications/287662-electrical-methods-of-soil-moisture-meas-d51cf882.pdf Electrical Methods of Soil Moisture Measurement: A Review]
 
**[https://media.neliti.com/media/publications/287662-electrical-methods-of-soil-moisture-meas-d51cf882.pdf Electrical Methods of Soil Moisture Measurement: A Review]
*Heat-diffusion
+
*Heat-diffusion [https://pubs.usgs.gov/wsp/1619u/report.pdf Reference (see Section C)]
*Absorption
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*Absorption [https://pubs.usgs.gov/wsp/1619u/report.pdf Reference (see Section D)]
 
*Tensiometric
 
*Tensiometric
 
**[https://www.youtube.com/watch?v=iss-XHRhfN4 Video]
 
**[https://www.youtube.com/watch?v=iss-XHRhfN4 Video]
**[https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.550.1584&rep=rep1&type=pdf Soil Moisture Tensiometer Materials and Construction]
+
**[https://www.ars.usda.gov/arsuserfiles/20360500/pdf_pubs/P0015.pdf Soil Moisture Tensiometer Materials and Construction]
*Penetration
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*Penetration [https://pubs.usgs.gov/wsp/1619u/report.pdf Reference (see Section F)]
 
*Radioactive
 
*Radioactive
 
**[https://www.youtube.com/watch?v=x_cegBUy1-I Video]
 
**[https://www.youtube.com/watch?v=x_cegBUy1-I Video]
 
**[https://www.youtube.com/watch?v=FAJqCjTFBVk Video neutron probe]
 
**[https://www.youtube.com/watch?v=FAJqCjTFBVk Video neutron probe]
  
===Bulk density===
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===[https://stormwater.pca.state.mn.us/index.php?title=Soil_hydrologic_properties_and_processes#Soil_water_and_water_retention Available water capacity]===
 +
Available water capacity is the maximum amount of plant available water a soil can provide, often calculated as water available between <span title="Field capacity is the amount of soil moisture or water content held in soil after excess water has drained away and the rate of downward movement has materially decreased, which usually takes place within 2–3 days after a rain or irrigation in pervious soils of uniform structure and texture."> '''field capacity'''</span> and the <span title="The wilting point, also called the permanent wilting point, may be defined as the amount of water per unit weight or per unit soil bulk volume in the soil, expressed in percent, that is held so tightly by the soil matrix that roots cannot absorb this water and a plant will wilt."> '''wilting point'''</span>.
 +
 
 +
This link provides a discussion of methods for determining available water capacity.
 +
*[https://grdc.com.au/resources-and-publications/grdc-update-papers/tab-content/grdc-update-papers/2018/07/soil-water-methods-to-predict-plant-available-water-capacity Soil water – methods to predict plant available water capacity (PAWC) using soil-landscape associations]
 +
*[https://csanr.wsu.edu/a-new-method-for-measuring-plant-available-water-capacity-helps-document-benefits-of-biochar-soil-mixtures/ A New Method for Measuring Plant Available Water Capacity Helps Document Benefits of Biochar-Soil Mixtures]
 +
*Video: [https://www.youtube.com/watch?v=yUTrXh05ZWE Soil Available Water Capacity Demonstration]
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*Video: [https://www.youtube.com/watch?v=ojCRX6ILzRY Soil Water Holding Capacity Determination Practical Experiment]
 +
*Video: [https://www.youtube.com/watch?v=36oTtMV0ZJo Calculating Plant Available Water]
 +
 
 +
===[https://stormwater.pca.state.mn.us/index.php?title=Soil_physical_properties_and_processes#Soil_density Bulk density]===
 
[https://stormwater.pca.state.mn.us/index.php?title=Soil_physical_properties_and_processes#Soil_density Soil bulk density] is an important measurement for determining soil infiltration and plant rooting properties. Measuring bulk density involves proper sample collection and laboratory analysis. Below are links to videos demonstrating methods for collecting bulk density samples.
 
[https://stormwater.pca.state.mn.us/index.php?title=Soil_physical_properties_and_processes#Soil_density Soil bulk density] is an important measurement for determining soil infiltration and plant rooting properties. Measuring bulk density involves proper sample collection and laboratory analysis. Below are links to videos demonstrating methods for collecting bulk density samples.
 
*[https://www.youtube.com/watch?v=C0Wu7FVPt6I Bulk density and soil water (moisture) content] - a 12 minute video illustrating how to collect the sample in field and measure in the lab using the core method
 
*[https://www.youtube.com/watch?v=C0Wu7FVPt6I Bulk density and soil water (moisture) content] - a 12 minute video illustrating how to collect the sample in field and measure in the lab using the core method
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Methods for measuring bulk density are provided in the following documents.
 
Methods for measuring bulk density are provided in the following documents.
*[http://soilquality.org.au/factsheets/bulk-density-measurement Bulk Density – Measurement]
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*[https://www.soilquality.org.au/factsheets/bulk-density-measurement Bulk Density – Measurement]
 
*[https://anlab.ucdavis.edu/analysis/Soils/480 Bulk Density - UC Davis]
 
*[https://anlab.ucdavis.edu/analysis/Soils/480 Bulk Density - UC Davis]
  
===Infiltration rate===
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===[https://stormwater.pca.state.mn.us/index.php?title=Soil_hydrologic_properties_and_processes#Soil_infiltration Infiltration rate]===
 +
[[File:MPD Infiltrometer image.jpg|300px|thumb|alt=image of MPD infiltrometer|<font size=3>The modified Philip-Dunne infiltrometer, as well as other direct infiltration measurements such as double ring infiltrometers, are preferred methods for measuring infiltration rates, compared to soil borings and pits. Image: [http://stormwaterbook.safl.umn.edu/water-budget-measurement/infiltration University of Minnesota, St. Anthony Falls Laboratory]</font size>.]]
 +
 
 
<span title="The infiltration rate is the velocity or speed at which water enters into the soil"> '''Infiltration rates'''</span> should be measured in the field. [https://stormwater.pca.state.mn.us/index.php?title=Determining_soil_infiltration_rates This page] provides information on measuring soil infiltration rates.
 
<span title="The infiltration rate is the velocity or speed at which water enters into the soil"> '''Infiltration rates'''</span> should be measured in the field. [https://stormwater.pca.state.mn.us/index.php?title=Determining_soil_infiltration_rates This page] provides information on measuring soil infiltration rates.
  
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*[https://www.youtube.com/watch?v=ugfUg4TeagU Guelph permeameter]
 
*[https://www.youtube.com/watch?v=ugfUg4TeagU Guelph permeameter]
 
*[https://www.youtube.com/watch?v=YawF0W8PBA0 Double ring infiltrometer]
 
*[https://www.youtube.com/watch?v=YawF0W8PBA0 Double ring infiltrometer]
*[https://www.youtube.com/watch?v=PYvfTxQhbOQ Double ring infiltraometer]
+
*[https://www.youtube.com/watch?v=PYvfTxQhbOQ Double ring infiltrometer]
 +
 
 +
===[https://stormwater.pca.state.mn.us/index.php?title=Alleviating_compaction_from_construction_activities Compaction (penetration resistance)]===
 +
[[File:Cone penetrometer.png|300px|thumb|alt=photo of cone penetrometer|<font size=3>Photo of cone penetrometer</font size>]]
  
===Compaction (penetration resistance)===
 
 
Soil compaction results from repeated traffic, generally from machinery, or repeated tillage at the same depth, which results in a compacted layer at the tillage depth. Compaction inhibits infiltration, gas and water movement, may impede root growth, disrupts habitat for soil biota, and affects nutrient cycling. There are several field methods for determining soil compaction or penetration resistance.
 
Soil compaction results from repeated traffic, generally from machinery, or repeated tillage at the same depth, which results in a compacted layer at the tillage depth. Compaction inhibits infiltration, gas and water movement, may impede root growth, disrupts habitat for soil biota, and affects nutrient cycling. There are several field methods for determining soil compaction or penetration resistance.
 
*'''Sand Cone Method''': The sand cone test is a relatively simple test that doesn't take long to perform, but does require drying soil samples. It is not suitable for saturated and soft soils. The method consists of digging a hole in a soil, determining the volume of the hole by filling the whole with sand of known dry density, determining the dry density of the soil removed from the whole, and computing percent compaction. The procedure is described [https://www.youtube.com/watch?v=ojH0W3xq3P0 in this video]. [https://www.dot.nd.gov/forms/sfn59725.pdf This worksheet] can be used to make the calculations. Calculations and procedures are also shown [https://www.civilconcept.com/sand-cone-test/ on this website].
 
*'''Sand Cone Method''': The sand cone test is a relatively simple test that doesn't take long to perform, but does require drying soil samples. It is not suitable for saturated and soft soils. The method consists of digging a hole in a soil, determining the volume of the hole by filling the whole with sand of known dry density, determining the dry density of the soil removed from the whole, and computing percent compaction. The procedure is described [https://www.youtube.com/watch?v=ojH0W3xq3P0 in this video]. [https://www.dot.nd.gov/forms/sfn59725.pdf This worksheet] can be used to make the calculations. Calculations and procedures are also shown [https://www.civilconcept.com/sand-cone-test/ on this website].
*'''Rubber balloon method''': Rubber Balloon Density test are similar to the sand cone method. A balloon density apparatus is positioned over the hole, and instead of using sand to measure volume, the calibrated water vessel is pressurized, forcing a rubber membrane into the excavation. Graduations on the vessel are read to determine the amount of water displaced so the whole volume can be calculated. The test method is described in ASTM D2167 / AASHTO T 205 (withdrawn). The tests simpler to perform than the sand cone and can be repeated quickly since the water is retained in the vessel.
+
*'''Rubber balloon method''': Rubber Balloon Density test are similar to the sand cone method. A balloon density apparatus is positioned over the hole, and instead of using sand to measure volume, the calibrated water vessel is pressurized, forcing a rubber membrane into the excavation. Graduations on the vessel are read to determine the amount of water displaced so the whole volume can be calculated. The test method is described in ASTM D2167 / AASHTO T 205 (withdrawn). The tests simpler to perform than the sand cone and can be repeated quickly since the water is retained in the vessel. [https://dot.nebraska.gov/media/9870/ndtt205.pdf Reference].
*'''Penetrometers''': Penetrometers measure the force needed to push a metal rod of known diameter into a growing medium. They may be hand operated or machine driven. The cone penetrometer, the most commonly used penetrometer, simulates a root growing through the soil. A hand operated unit is pushed into a soil and a gauge on the device measures the amount of force needed to penetrate the soil. [https://www.youtube.com/watch?v=Zq_785JqRq8 This video] demonstrates how to use a portable penetrometer in the field. While easy to use, there are some limitations. Measurements should be made when the soil is near field capacity. The device may have limitations in granular soils, clay soils, and soils with sharp boundary layers. For more information, including procedure descriptions and equipment needs, see [https://directives.sc.egov.usda.gov/OpenNonWebContent.aspx?content=31850.wba], [https://www.geoengineer.org/storage/publication/18455/publication_file/2694/KN3Ramsey.pdf], and [https://extension.psu.edu/diagnosing-soil-compaction-using-a-penetrometer-soil-compaction-tester].
+
*'''Penetrometers''': Penetrometers measure the force needed to push a metal rod of known diameter into a growing medium. They may be hand operated or machine driven. The cone penetrometer, the most commonly used penetrometer, simulates a root growing through the soil. A hand operated unit is pushed into a soil and a gauge on the device measures the amount of force needed to penetrate the soil. These videos ([https://www.youtube.com/watch?v=Zq_785JqRq8], [https://www.youtube.com/watch?v=S5Zt2qo63qY], [https://www.youtube.com/watch?v=PUvjeYAU3Oc]) demonstrate how to use penetrometers in the field. While easy to use, there are some limitations. Measurements should be made when the soil is near field capacity. The device may have limitations in granular soils, clay soils, and soils with sharp boundary layers. For more information, including procedure descriptions and equipment needs, see [https://directives.sc.egov.usda.gov/OpenNonWebContent.aspx?content=31850.wba], [https://www.geoengineer.org/storage/publication/18455/publication_file/2694/KN3Ramsey.pdf], and [https://extension.psu.edu/diagnosing-soil-compaction-using-a-penetrometer-soil-compaction-tester].
 
*'''Nuclear test''': Nuclear density gauges determine soil density by measuring gamma radiation transmission between a probe containing a radioactive Cesium 137 (or other) source and detection sensors in the base of the gauge. Dense soils allow fewer gamma particles to be detected in a given time period. Soil moisture is measured at the same time. Nuclear density gauges are efficient on large projects requiring rapid results and multiple tests but are subject to regulatory requirements and require advanced training and radiation dosage monitoring of personnel. Test methods are described in ASTM D6938 / AASHTO T 310.
 
*'''Nuclear test''': Nuclear density gauges determine soil density by measuring gamma radiation transmission between a probe containing a radioactive Cesium 137 (or other) source and detection sensors in the base of the gauge. Dense soils allow fewer gamma particles to be detected in a given time period. Soil moisture is measured at the same time. Nuclear density gauges are efficient on large projects requiring rapid results and multiple tests but are subject to regulatory requirements and require advanced training and radiation dosage monitoring of personnel. Test methods are described in ASTM D6938 / AASHTO T 310.
  
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'''Further reading'''
 
'''Further reading'''
 
*[https://www.ars.usda.gov/ARSUserFiles/30501000/SoilAggStabKit.pdf Field soil aggregate stability kit for soil quality and rangeland health assessments]
 
*[https://www.ars.usda.gov/ARSUserFiles/30501000/SoilAggStabKit.pdf Field soil aggregate stability kit for soil quality and rangeland health assessments]
*[https://attra.ncat.org/how-is-soil-aggregate-stability-tested/ How is soil aggregate stability tested?]
 
 
*[https://ballina.nsw.gov.au/files/Assessing%20Soil%20Aggregate%20Stability%20-%20Fact%20Sheet%205%20-%20V2.pdf Assessing soil aggregate stability]
 
*[https://ballina.nsw.gov.au/files/Assessing%20Soil%20Aggregate%20Stability%20-%20Fact%20Sheet%205%20-%20V2.pdf Assessing soil aggregate stability]
 
*[https://www.sciencedirect.com/science/article/pii/S0167198716302306 Evaluation of methods for determining soil aggregate stability]
 
*[https://www.sciencedirect.com/science/article/pii/S0167198716302306 Evaluation of methods for determining soil aggregate stability]
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*[https://www.youtube.com/watch?v=S1GogaMk8l8]
 
*[https://www.youtube.com/watch?v=S1GogaMk8l8]
  
===Texture===
+
===[https://stormwater.pca.state.mn.us/index.php?title=Soil_physical_properties_and_processes#Soil_texture Texture]===
 +
[[File:Sives.png|300px|thumb|alt=image of soil sieves|<font size=3>Soil sieves used to determine soil texture</font size>. [https://en.wikipedia.org/wiki/Creative_Commons Creative Commons] [https://creativecommons.org/licenses/by-sa/4.0/deed.en Attribution-Share Alike 4.0 International]]]
 +
 
 
Soil texture is determined with one of the following methods.
 
Soil texture is determined with one of the following methods.
*Mechanical sieving, if particle size > 0.05 mm
+
*Mechanical sieving, if particle size > 0.05 mm ([https://www.cbsd.org/cms/lib010/PA01916442/Centricity/Domain/1908/soil_sieve.pdf Reference])
 
*<span title="Sedimentation is the process by which solids are removed from the water column by settling. Sedimentation practices include dry ponds, wet ponds, wet vaults, and other devices."> [https://stormwater.pca.state.mn.us/index.php?title=Stormwater_sedimentation_Best_Management_Practices '''Sedimentation''']</span> if size < 0.05 mm. Sedimentation measures the settling rate of particles in liquid medium and relates this rate to the particle mass by use of the [https://en.wikipedia.org/wiki/Stokes%27_law <span title="The force required to move a sphere through a given viscous fluid at a low uniform velocity is directly proportional to the velocity and radius of the sphere."> '''Stoke's Law'''</span>]. Forces acting on soil particle are gravitation, buoyancy and drag forces, all of which depend on <span title="An index (means of expression) indicating what sizes (particle size) of particles are present in what proportions (relative particle amount as a percentage where the total amount of particles is 100 %) in the sample particle group to be measured"> '''particle size'''</span>. Larger particles settle first. The particle mass is determined by density and particle size. Soils must be dispersed prior to measurement. Two methods are commonly used.
 
*<span title="Sedimentation is the process by which solids are removed from the water column by settling. Sedimentation practices include dry ponds, wet ponds, wet vaults, and other devices."> [https://stormwater.pca.state.mn.us/index.php?title=Stormwater_sedimentation_Best_Management_Practices '''Sedimentation''']</span> if size < 0.05 mm. Sedimentation measures the settling rate of particles in liquid medium and relates this rate to the particle mass by use of the [https://en.wikipedia.org/wiki/Stokes%27_law <span title="The force required to move a sphere through a given viscous fluid at a low uniform velocity is directly proportional to the velocity and radius of the sphere."> '''Stoke's Law'''</span>]. Forces acting on soil particle are gravitation, buoyancy and drag forces, all of which depend on <span title="An index (means of expression) indicating what sizes (particle size) of particles are present in what proportions (relative particle amount as a percentage where the total amount of particles is 100 %) in the sample particle group to be measured"> '''particle size'''</span>. Larger particles settle first. The particle mass is determined by density and particle size. Soils must be dispersed prior to measurement. Two methods are commonly used.
 
**<span title="an instrument for measuring the density of liquids."> '''Hydrometer'''</span> method ([https://lter.kbs.msu.edu/protocols/108 see here for description])
 
**<span title="an instrument for measuring the density of liquids."> '''Hydrometer'''</span> method ([https://lter.kbs.msu.edu/protocols/108 see here for description])
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Other methods, which employ qualitative approaches, include the feel method, ball and ribbon methods, and ball throwing method. These [http://www.fao.org/3/ac172e/AC172E04.htm are described here].
 
Other methods, which employ qualitative approaches, include the feel method, ball and ribbon methods, and ball throwing method. These [http://www.fao.org/3/ac172e/AC172E04.htm are described here].
  
==Biologic tests and assessments==
+
===Soil structure===
 +
Measurement of soil structure typically focuses on determining soil stability and texture. See the methods above for measuring these properties. Additional references and links are provided below.
 +
*Video: [https://www.youtube.com/watch?v=Z9J6sWeblK8 How to test soil structure]
 +
*Video: [https://www.youtube.com/watch?v=ow7aHtbluXs How to determine soil structure]
 +
*[https://www.publish.csiro.au/SR/SR9910869 The measurement of soil structure - Some practical initiatives]
 +
*[https://www.upcycleandcompany.com/test-soil-structure/ How to test soil structure]
 +
*[https://kstatelibraries.pressbooks.pub/soilslabmanual/chapter/soil-texture-and-structure/ Soil Texture and Structure]
 +
*[https://www.awri.com.au/wp-content/uploads/v_activity_soil_structure.pdf A method for assessing soil structure]
  
===Biotic diversity===
+
===Surface crusting===
 +
[http://soilquality.org/indicators/soil_crusts.html Structural soil crusts] are relatively thin, dense, somewhat continuous layers of non-aggregated soil particles on the surface of tilled and exposed soils. A surface crust indicates poor infiltration, a problematical seedbed, and reduced air exchange between the soil and atmosphere. It can also indicate that a soil has a high sodium content that increases soil dispersion when it is wetted by rainfall or irrigation. Tests typically are based on applying pressure to determine the strength of a crust, or methods to determine stability of the surface crust.
  
===Soil structure===
+
Below are resources for measuring soil crusting and strength of crusts.
 +
*Video: [https://www.youtube.com/watch?v=U6aOei0xaEg SoilHealth Trainings 4: Surface Crusts (Surface Crusting)]
 +
*[https://agcrops.osu.edu/newsletter/corn-newsletter/2018-10/using-slake-test-determine-soil-crusting Using the Slake Test to Determine Soil Crusting]
 +
*[https://www.tandfonline.com/doi/abs/10.1080/00103627709366708?journalCode=lcss20 Soil crust strength measurement]
 +
*[https://www.jswconline.org/content/37/4/225 A technique for measuring soil crust strengths]
 +
*[https://www.ltsd.k12.pa.us/wp-content/uploads/2015/08/Soil-Crust.pdf Soil Quality Indicators: Soil Crusts]
  
===Surface crusting===
+
===[https://stormwater.pca.state.mn.us/index.php?title=Soil_hydrologic_properties_and_processes#Preferential_.28macropore.29_pore_flow_in_soil Macroporosity]===
 +
In soils with significant macroporosity, a high percentage of annual water and solute movement can occur within the macropores. This can lead to rapid movement of solutes, including pollutants of concern, deep into the soil profile and eventually into groundwater. Soil macroporosity can be measured directly in the field by physically excavating soil, typically in layers, and quantifying soil macropores. Colored or fluorescent dyes are often used, as well as imaging equipment. Examples of this methodology are provided at the following links.
 +
*[https://stormwater.pca.state.mn.us/index.php?title=Soil_hydrologic_properties_and_processes#Preferential_.28macropore.29_pore_flow_in_soil An Improved Method for Quantifying Soil Macroporosity]
 +
*[https://library.csbe-scgab.ca/docs/journal/41/41_1_23_ocr.pdf Quantification of soil macroporosity and its relationship with soil properties]
 +
*[https://web.engr.oregonstate.edu/~wildensd/Papers/Naveed_et_al_SSSAJ_2013.pdf Revealing Soil Structure and Functional Macroporosity along a Clay Gradient Using X-ray Computed Tomography]
 +
*[https://cdnsciencepub.com/doi/10.4141/cjss89-062 THE CHARACTERIZATION OF SOIL MACROPOROSITY WITH CT SCANNING]
  
===Macroporosity===
+
Macroporosity can also be estimated using indirect methods, such as those based on bulk density, water content, particle size distribution, and infiltration. Examples are provided at the following links.
 +
*[https://www.scielo.br/j/rbcs/a/QYcFLvyd5Ztzp6zFtLfjp6y/?format=pdf&lang=en METHOD TO ESTIMATE SOIL MACROPOROSITY AND MICROPOROSITY BASED ON SAND CONTENT AND BULK DENSITY]
 +
*[https://bsssjournals.onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2389.1988.tb01194.x The determination of the macroporosity of impregnated blocks of a clay soil and its relation to volumetric water content]
 +
*[https://acsess.onlinelibrary.wiley.com/doi/abs/10.2136/sssaj1986.03615995005000030007x Estimating Macroporosity in a Forest Watershed by use of a Tension Infiltrometer]
 +
*[https://acsess.onlinelibrary.wiley.com/doi/abs/10.2136/sssaj2010.0062 Quantitative Relationships between Soil Macropore Characteristics and Preferential Flow and Transport]
 +
*[https://acsess.onlinelibrary.wiley.com/doi/full/10.2136/vzj2018.08.0151 Effect of Macroporosity on Pedotransfer Function Estimates at the Field Scale]
  
===Available water capacity===
+
==Biotic diversity==
 +
There are currently two types of tests that can be performed to determine soil diversity: Tests that analyze and classify parts of the microbial material itself (‘taxonomic tests’), and tests that look at the metabolic products of microbes (‘functional tests’). Below are links to websites and videos that provide information on testing for biotic diversity, including testing methods.
 +
*[https://museum.isric.org/content/themestation/how-can-we-measure-soil-biodiversity/biodiversityb6 How can we measure soil biodiversity]: Provides a discussion of approaches to measuring soil biotic diversity
 +
*[https://museum.isric.org/content/themestation/how-can-we-measure-soil-biodiversity/biodiversityb6 SoilBio soil health test]
 +
*[http://soilfoodwebnewyork.com/files/biologicaltoolspart2.pdf Biological soil tests]
 +
*[https://vro.agriculture.vic.gov.au/dpi/vro/vrosite.nsf/pages/soilhealth_biology_tests#:~:text=The%20Biolog%20Plate%20test%20represents,communities%20can%20also%20be%20assessed. Soil Biological tests]
 +
*[https://academic.oup.com/femsec/article/82/1/1/564266 Standardisation of methods in soil microbiology: progress and challenges]
 +
*[https://www.sciencedirect.com/science/article/pii/S1631069110002921 Soil microbial diversity: Methodological strategy, spatial overview and functional interest]
 +
*[https://www.sciencedirect.com/science/article/abs/pii/S0167701204000983 Methods of studying soil microbial diversity]
 +
*[https://soils.vidacycle.com/soil-health/soil-lab-test-series/ Soil Lab Test Series #1: Soil Biodiversity Testing]: Provides links to sites that offer testing
 +
*Videos
 +
**[https://www.youtube.com/watch?v=joKBXCMupKo How to Measure Soil Biodiversity with Prof. Byrne]
 +
**[https://www.youtube.com/watch?v=ZWUV1xmw6oY Biology Lab - Soil Biodiversity]
 +
**[https://www.youtube.com/watch?v=ZiFodYiUBhQ Simple Soil Tests for Physical and Biological Soil Properties]
  
 
[[Category:Level 2 - Technical and specific topic information/soils and media]]
 
[[Category:Level 2 - Technical and specific topic information/soils and media]]

Latest revision as of 14:39, 11 January 2023

image

There are hundreds of soil tests that can be conducted, both in the field or laboratory. This page provides an overview of more common soil tests, links to information on sampling, and links to test methods.

Information: Soil sampling should be conducted by trained and, where appropriate, certified professionals, such as licensed soil scientists and geoscientists
Information: Laboratory tests should be done by certified laboratories. The Minnesota Department of Health Environmental Laboratory Accreditation Program develops procedures and requirements to ensure accredited laboratories produce accurate and precise test results. Search for an accredited lab.
Information: Reference or links to any specific commercial product, process, or service by trade name, trademark, service mark, manufacturer, or otherwise does not constitute or imply endorsement, recommendation, or favoring by the Minnesota Pollution Control Agency.

Sample collection

image of sampling rig
Example of direct push technology used to collect a soil sample.

Soil sample collection methods vary and covering all acceptable methods is beyond the scope of this page. Below are links to sampling methods, including videos.

Documents

Videos of sample collection for lab analysis

Chemical tests

Most chemical tests are conducted in the laboratory on samples collected in the field.

Recommended holding times and preservation

Nutrients

For more information link here.

Soil macronutrients include phosphorus, nitrogen, potassium, sulfur, calcium, and magnesium. Phosphorus is an important pollutant of concern in surface water, particularly lakes. Though there are several forms of phosphorus, they can roughly be divided into dissolved phosphorus (includes orthophosphate and soluble phosphorus) and particulate phosphorus, with dissolved phosphorus being much more bioavailable than particulate forms. Dissolved phosphorus is typically identified as phosphorus passing through a 0.45 micron filter. For a detailed discussion of phosphorus, link here.

Nitrogen is also an important nutrient in both surface water and groundwater. Nitrogen concentrations in stormwater are typically below levels of concern for receiving waters.

Potassium, sulfur, calcium, and magnesium are typically not pollutants of concern in stormwater runoff, but they may be deficient in some soils and therefore potentially impact vegetation.

Metals

The primary sources of metals in stormwater runoff are associated with automobiles, both from fluids and wear of parts, including tires. Concentrations of metals in stormwater runoff are generally below aquatic life and drinking water criteria, though concentrations may exceed criteria for sensitive species and in specific land uses, such as high traffic transportation areas. Metals of greatest concern include copper, zinc, nickel, cadmium, and lead.

Samples are typically collected for total metals, meaning samples are not filtered. For dissolved metal concentrations, samples are filtered using a 0.45 micron filter. From an environmental perspective, dissolved metal concentrations more accurately reflect potential risk to receptors, since most metal bound to particles is retained in stormwater bmps. Lab methods include the following.

pH

Soil pH typically ranges from 6 to 8. Soils with elevated organic matter concentrations may have lower pH. Soil pH affects biologic activity and chemical reactions, particularly of some metals. Soil pH is generally not a concern, though some amendments, such as lime (increases pH), may lead to soil pH values that adversely affect soil biology, vegetation, mobilize metals, or bind up nutrients. Recommended lab methods include the following.

Organic matter and carbon

By itself, organic matter is not generally a pollutant of concern unless it contains bound pollutants at levels of concern (e.g. metals, organic pollutants such as oil and pesticides). Organic matter can create oxygen demand in receiving waters and, as mentioned above, transport attached chemicals that may become a concern in receiving waters, including nutrients, metals , and organic pollutants. Organic matter also provides a food source for bacteria and pathogens.

Exchange capacity

Exchange capacity affects the fate of other soil chemicals, including nutrients and pollutants, and provides a buffer against soil acidification.

Enzyme activity

Enzymes in soil mediate numerous chemical reactions involved in soil nutrient cycling, transformation of plant and microbial debris, mineralization and transformation of organic matter within the carbon cycle, and transformation and degradation of potentially hazardous pollutants.

  • Fluorescence assays - synthetic C-, N-, or P-rich substrates bound with a fluorescent dye are added to soil samples. When intact, the labeled substrates do not fluoresce. Enzyme activity is measured as the increase in fluorescence as the fluorescent dyes are cleaved from their substrates, which allows them to fluoresce. Enzyme measurements can be expressed in units of molarity or activity. See this article and associated video for a description of the method.
  • Spectrophotometric assays - the course of the enzymatic reaction is followed by measuring a change in how much light the assay solution absorbs
  • Calorimetric assays - measure the heat released or absorbed by chemical reactions. These assays are very general.
  • Radiometric assays - measure the incorporation of radioactivity into substrates or its release from substrates. These assays are both extremely sensitive and specific.
  • Chromatographic assays - measure product formation by separating the reaction mixture into its components by chromatography. This is usually done by high-performance liquid chromatography (HPLC), but can also use thin layer chromatography.

Specific recommended procedures are not provided as there is a wide range of methods depending on objectives of the sampling. This video provides a discussion of enzymes and soil enzymes, including sample collection and measurement (starting at about the 39 minute mark). This website provides a discussion of soil enzymes including limitations of testing methods. Additional references include the following.

Field methods

Field methods for soil chemical testing are generally not recommended, though they can be useful in providing general information. Typically field tests involve the use of test strips or probes. Portable laboratories can be used to conduct some of the analyses described above. Although these tests are conducted in the field, they utilize laboratory methods and are therefore more appropriately considered lab tests.

Here are some links to information on soil chemical field tests.

Tests for soil physical and hydrologic properties

Most soil physical and hydrologic tests can be done in the field, but some require additional procedures performed in the laboratory.

Soil water (moisture) content

photo of soil tensiometer
Example of a tensiometer's vacuum gauge. Credit: Tina Dispenza, University of Florida/IFAS

Laboratory analysis of soil water content is recommended for point-in-time measurements. Lab methods involve weighing a soil sample prior to drying, then drying to constant weight in oven at temperature between 100–110oC (105oC is typical). The difference in weight represents the mass of water in the sample. The water content is then expressed on a mass basis (g of water to g of dry soil), or if the bulk density is known, the volume of water to volume of soil. It is important that samples collected in the field be properly stored to avoid water loss prior to analysis. For further reading see [4].

For continuous measurements, field methods must be employed. Field methods are summarized below. The most common methods are electrical resistance (e.g. time domain reflectometry), tensiometric, and radioactive (e.g. neutron probe). This document and this document provide discussions of methods for measuring soil water content. This one hour video provides an overview of soil water measurement.

Available water capacity

Available water capacity is the maximum amount of plant available water a soil can provide, often calculated as water available between field capacity and the wilting point.

This link provides a discussion of methods for determining available water capacity.

Bulk density

Soil bulk density is an important measurement for determining soil infiltration and plant rooting properties. Measuring bulk density involves proper sample collection and laboratory analysis. Below are links to videos demonstrating methods for collecting bulk density samples.

Methods for measuring bulk density are provided in the following documents.

Infiltration rate

image of MPD infiltrometer
The modified Philip-Dunne infiltrometer, as well as other direct infiltration measurements such as double ring infiltrometers, are preferred methods for measuring infiltration rates, compared to soil borings and pits. Image: University of Minnesota, St. Anthony Falls Laboratory.

Infiltration rates should be measured in the field. This page provides information on measuring soil infiltration rates.

Videos illustrating measurement of infiltration rates.

Compaction (penetration resistance)

photo of cone penetrometer
Photo of cone penetrometer

Soil compaction results from repeated traffic, generally from machinery, or repeated tillage at the same depth, which results in a compacted layer at the tillage depth. Compaction inhibits infiltration, gas and water movement, may impede root growth, disrupts habitat for soil biota, and affects nutrient cycling. There are several field methods for determining soil compaction or penetration resistance.

  • Sand Cone Method: The sand cone test is a relatively simple test that doesn't take long to perform, but does require drying soil samples. It is not suitable for saturated and soft soils. The method consists of digging a hole in a soil, determining the volume of the hole by filling the whole with sand of known dry density, determining the dry density of the soil removed from the whole, and computing percent compaction. The procedure is described in this video. This worksheet can be used to make the calculations. Calculations and procedures are also shown on this website.
  • Rubber balloon method: Rubber Balloon Density test are similar to the sand cone method. A balloon density apparatus is positioned over the hole, and instead of using sand to measure volume, the calibrated water vessel is pressurized, forcing a rubber membrane into the excavation. Graduations on the vessel are read to determine the amount of water displaced so the whole volume can be calculated. The test method is described in ASTM D2167 / AASHTO T 205 (withdrawn). The tests simpler to perform than the sand cone and can be repeated quickly since the water is retained in the vessel. Reference.
  • Penetrometers: Penetrometers measure the force needed to push a metal rod of known diameter into a growing medium. They may be hand operated or machine driven. The cone penetrometer, the most commonly used penetrometer, simulates a root growing through the soil. A hand operated unit is pushed into a soil and a gauge on the device measures the amount of force needed to penetrate the soil. These videos ([5], [6], [7]) demonstrate how to use penetrometers in the field. While easy to use, there are some limitations. Measurements should be made when the soil is near field capacity. The device may have limitations in granular soils, clay soils, and soils with sharp boundary layers. For more information, including procedure descriptions and equipment needs, see [8], [9], and [10].
  • Nuclear test: Nuclear density gauges determine soil density by measuring gamma radiation transmission between a probe containing a radioactive Cesium 137 (or other) source and detection sensors in the base of the gauge. Dense soils allow fewer gamma particles to be detected in a given time period. Soil moisture is measured at the same time. Nuclear density gauges are efficient on large projects requiring rapid results and multiple tests but are subject to regulatory requirements and require advanced training and radiation dosage monitoring of personnel. Test methods are described in ASTM D6938 / AASHTO T 310.

For additional information on measuring soil compaction, see [11], [12], and [13].

Aggregate stability

Non-granular soils (e.g. clays) form aggregates that are important in maintaining soil physical, chemical, and biologic processes. Methods for assessing aggregate stability are somewhat qualitative and different methods do not correlate well. The method selected should simulate field processes likely to affect aggregate stability (e.g. rainfall impact, ponded (flooded) conditions, tillage).

  • Sieve or strainer method: The most commonly used method for testing aggregate stability involves placing a soil sample on a nest of soil sieves with screen sizes typically ranging from 1 mm to 45 microns and then moving this nest of sieves up and down in a bucket of water. The more stable aggregates will stay on the top sieve, while less stable aggregates will move through the larger sieves to the finer sieves. Soil stability is assessed by measuring the mass of soil remaining, as a percent of initial soil mass, on the sieve after a specified number of dipping cycles (e.g. 5 cycles). Soils with high aggregate stability will typically retain 50 percent or more of the initial soil mass. This method may represent stability under rainfall.
  • Slake test: Dried aggregates are placed into a container filled with water. Assess the aggregates after specified times (e.g. 20 minutes, 2 hours, 20 hours). This method may represent stability under flooded (water immersed) conditions.
  • Vibration methods: An ultrasonic probe immersed in water containing soil aggregates vibrates at different vibration amplitudes. Soil stability is assessed after specific time intervals. This method may represent stability under tillage conditions.

Further reading

Videos

Texture

image of soil sieves
Soil sieves used to determine soil texture. Creative Commons Attribution-Share Alike 4.0 International

Soil texture is determined with one of the following methods.

  • Mechanical sieving, if particle size > 0.05 mm (Reference)
  • Sedimentation if size < 0.05 mm. Sedimentation measures the settling rate of particles in liquid medium and relates this rate to the particle mass by use of the Stoke's Law. Forces acting on soil particle are gravitation, buoyancy and drag forces, all of which depend on particle size. Larger particles settle first. The particle mass is determined by density and particle size. Soils must be dispersed prior to measurement. Two methods are commonly used.

Other methods, which employ qualitative approaches, include the feel method, ball and ribbon methods, and ball throwing method. These are described here.

Soil structure

Measurement of soil structure typically focuses on determining soil stability and texture. See the methods above for measuring these properties. Additional references and links are provided below.

Surface crusting

Structural soil crusts are relatively thin, dense, somewhat continuous layers of non-aggregated soil particles on the surface of tilled and exposed soils. A surface crust indicates poor infiltration, a problematical seedbed, and reduced air exchange between the soil and atmosphere. It can also indicate that a soil has a high sodium content that increases soil dispersion when it is wetted by rainfall or irrigation. Tests typically are based on applying pressure to determine the strength of a crust, or methods to determine stability of the surface crust.

Below are resources for measuring soil crusting and strength of crusts.

Macroporosity

In soils with significant macroporosity, a high percentage of annual water and solute movement can occur within the macropores. This can lead to rapid movement of solutes, including pollutants of concern, deep into the soil profile and eventually into groundwater. Soil macroporosity can be measured directly in the field by physically excavating soil, typically in layers, and quantifying soil macropores. Colored or fluorescent dyes are often used, as well as imaging equipment. Examples of this methodology are provided at the following links.

Macroporosity can also be estimated using indirect methods, such as those based on bulk density, water content, particle size distribution, and infiltration. Examples are provided at the following links.

Biotic diversity

There are currently two types of tests that can be performed to determine soil diversity: Tests that analyze and classify parts of the microbial material itself (‘taxonomic tests’), and tests that look at the metabolic products of microbes (‘functional tests’). Below are links to websites and videos that provide information on testing for biotic diversity, including testing methods.

This page was last edited on 11 January 2023, at 14:39.