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− | Soil health is an assessment of how well soil performs all of its functions now and how those functions are being preserved for future use. The assessment of soil health depends on the desired functions of the soil. In agricultural applications, for example, soil health is determined by assessing properties that affect plant growth, such nutrient status, pH, and bulk density. | + | Soil health is an assessment of how well soil performs all of its functions now and how those functions are being preserved for future use. The assessment of soil health depends on the desired functions of the soil. In agricultural applications, for example, soil health is determined by assessing properties that affect plant crop growth, such nutrient status, pH, and bulk density. |
For stormwater applications, soil health can be assessed for the following functions. | For stormwater applications, soil health can be assessed for the following functions. | ||
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*Ability to minimize erosion | *Ability to minimize erosion | ||
− | + | Assessments of soil health are typically done by using indicators. Indicators are measurable properties of soil or plants that provide clues about how well the soil can function. Indicators can be physical, chemical, and biological properties or processes. The adjacent table illustrates which indicators are useful in evaluating the four functions identified above. | |
− | == | + | ==Soil compaction (bulk density)== |
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[[File:Penetrometer curve.jpg|300px|thumb|alt=curve showing relationship of root penetration and penetration resistance|<font size=3>Curve showing relationship of root penetration and penetration resistance. Source: [https://extension.psu.edu/diagnosing-soil-compaction-using-a-penetrometer-soil-compaction-tester Penn State University Extension].</font size>]] | [[File:Penetrometer curve.jpg|300px|thumb|alt=curve showing relationship of root penetration and penetration resistance|<font size=3>Curve showing relationship of root penetration and penetration resistance. Source: [https://extension.psu.edu/diagnosing-soil-compaction-using-a-penetrometer-soil-compaction-tester Penn State University Extension].</font size>]] | ||
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{{:General relationship of soil bulk density to root growth based on soil texture}} | {{:General relationship of soil bulk density to root growth based on soil texture}} | ||
− | == | + | ==Water stable aggregates== |
'''Importance''': Stable soil <span title="Soil aggregation involves the binding together of several soil particles into secondary units"> '''aggregates'''</span>, in the presence of water, is important for water and air transport, root growth, habitat for soil biota, minimizing soil erodibility, protecting soil organic matter, and nutrient cycling. | '''Importance''': Stable soil <span title="Soil aggregation involves the binding together of several soil particles into secondary units"> '''aggregates'''</span>, in the presence of water, is important for water and air transport, root growth, habitat for soil biota, minimizing soil erodibility, protecting soil organic matter, and nutrient cycling. | ||
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*Vibration methods: An ultrasonic probe immersed in water containing soil aggregates vibrates at different vibration amplitudes. This method may represent stability under tillage conditions. | *Vibration methods: An ultrasonic probe immersed in water containing soil aggregates vibrates at different vibration amplitudes. This method may represent stability under tillage conditions. | ||
− | === | + | ==Soil structure crusting, and macroporosity== |
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+ | ==Available water capacity== | ||
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+ | ==Infiltration== | ||
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+ | ==Organic matter and organic carbon== | ||
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+ | ==Soil electrical conductivity== | ||
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+ | ==Biotic assessment (diversity)== | ||
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+ | ==Soil Enzymes== | ||
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+ | ==Soil Respiration== | ||
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+ | ==Plant roots== | ||
− | == | + | |
+ | ==Nutrient status (fertility)== | ||
{{alert|An excellent resource applicable to a wide variety of vegetated stormwater BMPs, including bioretention BMPs, is [https://www.pca.state.mn.us/water/plants-stormwater-design Plants for stormwater design] by Shaw and Schmidt (2003).|alert-info}} | {{alert|An excellent resource applicable to a wide variety of vegetated stormwater BMPs, including bioretention BMPs, is [https://www.pca.state.mn.us/water/plants-stormwater-design Plants for stormwater design] by Shaw and Schmidt (2003).|alert-info}} | ||
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*[https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/health/assessment/?cid=stelprdb1237387 Soil Quality Indicator Sheets] - see Chemical Indicators | *[https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/health/assessment/?cid=stelprdb1237387 Soil Quality Indicator Sheets] - see Chemical Indicators | ||
− | == | + | ==pH== |
− | == | + | ==Soil contamination== |
'''Importance''': Soils may contain concentrations of certain chemicals that are toxic to plants. Pollutants of greatest concern include metals (copper, lead, cadmium, nickel, zinc), sodium and chloride from road salt application, pesticides, and some hydrocarbons (e.g. oil, PAHs). Sites with known contamination may contain other pollutants, such as arsenic, but these soils are generally not suitable for stormwater applications without remediation. | '''Importance''': Soils may contain concentrations of certain chemicals that are toxic to plants. Pollutants of greatest concern include metals (copper, lead, cadmium, nickel, zinc), sodium and chloride from road salt application, pesticides, and some hydrocarbons (e.g. oil, PAHs). Sites with known contamination may contain other pollutants, such as arsenic, but these soils are generally not suitable for stormwater applications without remediation. | ||
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{{:Pollutants of concern from operations}} | {{:Pollutants of concern from operations}} | ||
− | == | + | ==Relating indicators to function== |
+ | |||
+ | ==Soil health - additional reading== | ||
*[https://www.nrcs.usda.gov/wps/portal/nrcs/main/soils/health/assessment/ Soil Health Assessment] - USDA-NRCS | *[https://www.nrcs.usda.gov/wps/portal/nrcs/main/soils/health/assessment/ Soil Health Assessment] - USDA-NRCS | ||
*[https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/health/assessment/?cid=stelprdb1237387 Soil Quality Indicator Sheets] - USDA-NRCS | *[https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/health/assessment/?cid=stelprdb1237387 Soil Quality Indicator Sheets] - USDA-NRCS |
Indicators for determining soil health | ||||
Indicator | Vegetative growth | Soil biotic function | Soil hydrologic function | Soil erosion potential |
Compaction/bulk density | Yes | Yes | Yes | If surface compacted |
Water stable aggregates | Yes | |||
Soil nutrient status | Yes | |||
Soil structure | Yes | |||
Plant roots | Yes |
Soil health is an assessment of how well soil performs all of its functions now and how those functions are being preserved for future use. The assessment of soil health depends on the desired functions of the soil. In agricultural applications, for example, soil health is determined by assessing properties that affect plant crop growth, such nutrient status, pH, and bulk density.
For stormwater applications, soil health can be assessed for the following functions.
Assessments of soil health are typically done by using indicators. Indicators are measurable properties of soil or plants that provide clues about how well the soil can function. Indicators can be physical, chemical, and biological properties or processes. The adjacent table illustrates which indicators are useful in evaluating the four functions identified above.
Importance: 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. See Soil physical properties and processes for a discussion of bulk density.
Assessment There are multiple methods for measuring bulk density and compaction (resistance). See methods for measuring and methods for measuring compaction. Recommended methods of assessment include the following.
General relationship of soil bulk density to root growth based on soil texture
Link to this table
Soil texture | Ideal bulk densities (g/cm3) | Bulk densities that may affect plantgrowth (g/cm3) | Bulk densities that restrict root growth (g/cm3) |
---|---|---|---|
sands, loamy sands | <1.60 | 1.69 | >1.80 |
sandy loams, loams | <1.40 | 1.63 | >1.80 |
sandy clay loams, loams, clay loams | <1.40 | 1.60 | >1.75 |
silts, silt loams | <1.30 | 1.60 | >1.75 |
silt loams, silty clay loams | <1.40 | 1.55 | >1.65 |
sandy clays, silty clays, clay loams with 35-45% clay | <1.10 | 1.49 | >1.58 |
clays (>45% clay) | <1.10 | 1.39 | >1.47 |
Importance: Stable soil aggregates, in the presence of water, is important for water and air transport, root growth, habitat for soil biota, minimizing soil erodibility, protecting soil organic matter, and nutrient cycling.
Assessment: 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). For more information about aggregate stability tests, link here.
Evaluating the nutrient status of a soil focuses on determining if a soil is deficient in one or more macronutrients (nitrogen (N), potassium (K), sulfur (S), calcium (Ca), and magnesium (Mg)) or micronutrients (boron (B), zinc (Zn), manganese (Mn), iron (Fe), copper (Cu), molybdenum (Mo), and chloride (Cl)). Additional parameters may include organic matter, pH, soluble salts, and cation exchange capacity.
Importance: Soil nutrients are essential for plant growth and soil biotic processes essential to plant growth. Soil pH of 5-8 is typically acceptable for plant growth and biotic processes, but outside this range metals may be mobilized and other biologic processes adversely affected. Cation exchange capacity is a measure of a soils ability to retain nutrients that can be used by soil biota, including plants. Soluble salts may build up in soils after excess fertilizer applications, leading to drought stress in plants. Soil organic matter serves many functions in soil, including supplying nutrients, improving water storage and transport, improving soil structure and aggregation, and providing habitat for soil biota.
Assessment: Most Minnesota soils with organic matter are not deficient in soil micronutrients, Ca, Mg, or S. Thus, testing for organic matter, pH, N, P, and K is generally sufficient. Organic matter is analyzed in a laboratory, while the other parameters can be tested in the field. For purposes of assessing soil nutrient status or fertility, field tests are generally adequate. Lab tests provide more accurate results and some labs offer standard soil tests that assess soil fertility. Links to videos discussing and demonstrating field testing are provided below.
Video links for field testing
Further reading
Importance: Soils may contain concentrations of certain chemicals that are toxic to plants. Pollutants of greatest concern include metals (copper, lead, cadmium, nickel, zinc), sodium and chloride from road salt application, pesticides, and some hydrocarbons (e.g. oil, PAHs). Sites with known contamination may contain other pollutants, such as arsenic, but these soils are generally not suitable for stormwater applications without remediation.
Assessment: Risk assessments for metals concentrations in soil are generally based on human exposure, and there is limited information on toxic concentrations for different plants. Nevertheless, most urban soils do not contain chemicals at concentrations which restrict plant growth, although concentrations of these chemicals are typically greater than natural background ([1], [file:///C:/Users/franc/Downloads/environments-07-00098-v2.pdf], [2], [3], [4], [5], [6]). Chemical sampling is expensive, particularly for organic contaminants. An assessment of soil contamination should therefore begin with a site investigation to identify the presence of contaminant sources or historical activities that may have resulted in soil contamination.
Regardless of the results for a site visit and site review, soil sampling is warranted for certain land use settings. The adjacent table provides a summary of potential pollutant concerns for specific land uses. If sampling is warranted, use appropriate sampling and test methods, described on this page.
Pollutants of Concern from Operations (adapted from CWP, 2005).
Link to this table.
Pollutant of concern | Vehicle operations | Waste management | Site maintenance practices | Outdoor materials | Landscaping |
---|---|---|---|---|---|
Nutrients | X | X | X | ||
Pesticides | X | X | |||
Solvents | X | X | |||
Fuels | X | ||||
Oil and grease | X | X | |||
Toxic chemicals | X | X | |||
Sediment | X | X | X | X | |
Road salt | X | X | |||
Bacteria | X | X | |||
Trace metals | X | X | |||
Hydrocarbons | X | X |