Soil sampling and tests

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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.

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.

Laboratory tests

Below is a list of recommended laboratory tests

Nutrients

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.

• Phosphorus
  • Bray Method: use on acidic and neutral soils
  • Olsen Method: preferred on high pH soils
  • Mehlich-3 Method: provides a better indicator of plant-available phosphorus
• Nitrogen
  • Soil Nitrate And Extractable Ammonium By Flow Injection Analyzer Method (cadmium reduction method)
  • Total Kjeldahl nitrogen (wet oxidation method)
  • Total Nitrogen And Carbon - Combustion Method (Dumas Method)]
• Potassium, Sodium, Calcium, Magnesium, Boron and sulfate-Sulfur
  • Inductively Coupled Plasma Emission Spectrometry (ICP-AES) - recommended due to lower detection limits
  • atomic absorption spectroscopy

Metals

• Inductively Coupled Plasma Emission Spectrometry (ICP-AES) - recommended due to lower detection limits
• atomic absorption spectroscopy

pH

• Saturated paste - recommended
• 1:1 and 2:1 water ratios

Organic matter and carbon

• organic carbon combustion
• organic matter Walkley-Black
• 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

• Cation exchange capacity - multiple methods are available for cation exchange capacity. For more information read here.
  • 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
  • Agronomic Soil Tests - estimates CEC from test extractable Ca, K, and Mg and some rapid measure of exchangeable acidity (see next bullet)
• Exchangeable Potassium, Calcium, Magnesium, Sodium And Estimated Cation Exchange Capacity

Field methods

• Soil water (moisture) content
  • Electrical-resistance
  • Heat-diffusion
  • Absorption
  • Tensiometric
  • Penetration
  • Radioactive

Combined field and lab methods

• 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
• Bulk density and soil water (moisture) content - a 10 minute video using the core method
• Bulk density and soil water (moisture) content - this 34 minute video describes the clod method, which is preferred but more time consuming and cannot be used for soils where intact clods cannot be collected

Sample collection

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

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.

• US EPA - focus on VOCs and PFAS
• Testing Your Soil Why and How to Take a Soil-Test Sample - University of Hawaii
• Sampling Soils for Nutrient Management - USDA-NRCS; focus on phosphorus
• Procedure for taking soil samples - Stephen F. Austin State University
• Guidelines for Soil Sampling - USDA-NRCS
• Soil Sampling Guidelines - Purdue University
• Composite Soil Sampling - MCSE - Kellogg Biological Station
• Soil sample collection and analysis procedures - MPCA Petroleum Remediation Program
• Quality Assurance Project Plan Midland Area Soil Sampling, Midland Michigan
• Soil Sampling Quality Assurance User's Guide - US EPA