|Links to sections on this page|
|Chemical laboratory tests|
|Exchange capacity (cation exchange capacity)|
|Soil electrical conductivity|
|Organic matter and organic carbon|
|Chemical field tests|
|Tests for soil physical properties|
|Soil water (moisture) content|
|Available water capacity|
|Biologic tests and assessments|
|Biotic assessment (diversity)|
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.
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.
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.
Videos of sample collection for lab analysis
Below is a list of recommended laboratory tests.
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 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.
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.
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.
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.
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.
Most soil physical soil tests can be done in the field, but some require additional procedures performed in the laboratory.
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 .
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.
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 rates should be measured in the field. This page provides information on measuring soil infiltration rates.
Videos illustrating measurement of infiltration rates.
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.
Non-granular soils (e.g. sands) 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).
Soil texture is determined with one of the following methods.
Other methods, which employ qualitative approaches, include the feel method, ball and ribbon methods, and ball throwing method. These are described here.