Soil test

For other uses, see Geotechnical investigation.

In agriculture, a soil test is the analysis of a soil sample to determine nutrient content, composition and other characteristics, including contaminants. Tests are usually performed to measure the expected growth potential of a soil. It measures fertility, indicates deficiencies that need to be remedied and determine potential toxicities from excessive fertility and inhibitions from the presence of non-essential trace minerals. The test is used to mimic the function of roots to assimilate minerals. The expected rate of growth is modeled by the Law of the Maximum.

Soil sampling

The quality of the original soil sample plays a key role in determining the practical value of test results. Most labs will provide documentation outlining the proper procedures for collecting soil samples.

Labs, such as Iowa State and Colorado State University, recommend that you take between 10-20 samples for every 40 acres (160,000 m²) of the field. Sampling implements must be properly cleaned prior to sampling, and must be cleaned between samples to avoid cross-contamination (especially when sampling and testing for soil contaminants). The tool should be free of rust, and washed with distilled water. Doing so will clean the tool, but also not add any minerals or elements from regular tap water or chemicals that could change the composition of the soil.

Soil characteristics can vary significantly from one spot to another, even in a small garden or field. Taking samples everywhere in the field is crucial to get the most accurate measurement of nutrients and other organisms. An example of this is along gravel roads where the soil could have more lime from the dust from the roads settling down in the soil, or an old animal feedlot where phosphorus and nitrogen counts could be higher than the rest of the field.

Sample depth is also an important factor. It is recommended that you take the samples from tillage depth, as this is where the majority of the nutrients and elements are placed mechanically. The presence of various nutrients and other soil components varies during the year, so sample timing may also be important. A good time to take a sample for testing is in the fall after harvesting is finished, but this isn't the only time it should be done.

Sampling and testing in the fall is beneficial because the producer will get the results back in time to formulate the fertilizer plan for the following growing season. Another time sampling and testing can be done is spring. This is a good way to see what nutrients survive over winter when the soil freezes, as well as if any leaches away from melting of snow and thawing of the soil. This way the producer can know if more or less fertilizer needs to be purchased.

Mixing soil from several locations to create an "average" (or "composite") sample is a common procedure but it must be used judiciously as it can artificially dilute quantities/concentrations of soil components and may not meet government agency requirements for sampling. Make a reference map for your filing system so you know where you took them, and how many samples you took in the field. All of these considerations affect the interpretation of test results.

Storage and handling

Because certain characteristics of soil change with time it is essential that soil is analyzed as soon as practical. If it can not be tested within 24 hours of sampling soil should be frozen to reduce changes due to biological and chemical activity. Longer periods between sampling and testing may require the soil to be air dried. Properly dried soil may be stable for periods of 6 months or more.

Soil testing

Soil testing is often performed by commercial labs that offer an extensive array of specific tests. Choosing the test lab site is just as important as the test results. There are many soil testing labs in the United States, but finding the right one for you will take some research. It is most beneficial for the producer to find the local most lab, as the workers will have a greater knowledge and more experience working with the local soils.

Tests include, but aren't limited to, major nutrients - nitrogen (N), phosphorus (P), and potassium (K), secondary nutrients - sulphur, calcium, magnesium, minor nutrients - iron, manganese, copper, zinc, boron, molybdenum, aluminum.

Soil testing can be an easy, cost effective way to manage agronomic as well as horticultural soils. It tells key nutrient levels, as well as pH levels, so the producer can make the best choice when purchasing fertilizers and other nutrients.

Recently (2004) new prepaid mail-in kits have come to market that offer two specific benefits to small acreage farmers, urban homeowners and the lawn care industry: first is an inexpensive and quick manner to transfer soil samples directly to an accreditted laboratory for analysis; and second, the process translates raw data findings (as listed above: Tests include,...") into workable and practical nutrient management/fertilizer reports. One such kit can be viewed at Grass Roots. This particular process provides an actual 'prescription' of fertilizers that are readily available in the global market for two complete seasons.

Less comprehensive do-it-yourself kits are also available, usually with tests for three important plant nutrients - nitrogen (N), phosphorus (P), and potassium (K) - and for soil acidity (pH). Do-it-yourself kits can usually be purchased at your local cooperative or through the university or private lab you choose. Prices of the tests will vary on the lab/university you purchase it from and also on what kind of test you want to do. Lab tests are more accurate, though both types are useful. In addition, lab tests frequently include professional interpretation of results and recommendations. Always refer to all proviso statements included in a lab report - these may outline any anomalies, exceptions and shortcomings in the sampling and/or analytical process/results.

lettuce) and on the surface of root crops (e.g., carrots)." UMinn

Lead Level / Extracted Lead (ppm) / Estimated Total Lead (ppm)

Low / less than 43 / less than 500*

Medium / 43 to 126 / 500 to 1000

High / 126 to 480 / 1000 to 3000

Very High / greater than 480 / greater than 3000

(*) If estimated total soil lead levels are above 300 ppm, however, young children and pregnant women should avoid soil contact.

Good Gardening Practices to Reduce the Lead Risk

1. Locate gardens away from old painted structures and heavily traveled roads.

2. Give planting preferences to fruiting crops (tomatoes, squash, peas, sunflowers, corn, etc.).

3. Incorporate organic materials such as finished compost, humus, and peat moss.

4. Lime soil as recommended by soil test (pH 6.5 minimizes lead availability).

5. Discard old and outer leaves before eating leafy vegetables. Peel root crops. Wash all produce.

6. Keep dust to a minimum by maintaining a mulched and/or moist soil surface.

Some laboratories analyze for all 14 mineral nutrients and a dozen non-essential, potentially toxic mineral utilizing the “universal soil extractant” (ammonium bicarbonate DTPA) reference

Soil Contaminants

Common mineral soil contaminants include:

Arsenic, Barium, Cadmium, Copper, Mercury, Lead, Zinc.

Soil Contaminants References:

• Pollutants/Toxics > Soil Contaminants
• Common Contaminants Environmental Protection Agency - www.epa.gov

See also

• Fertilizer
• Plant tissue test
• Geotechnical investigation
• Liming (soil)
• ["One Hundred Harvests Research Branch Agriculture Canada 1886-1986". Historical series / Agriculture Canada - Série historique / Agriculture Canada. Government of Canada. http://epe.lac-bac.gc.ca/100/205/301/ic/cdc/agrican/pubweb/hs270060.asp.]

References

• Soil Test Learn about Soil, Percolation, Perc and Perk Tests.
• Colorado State University Extension Service
• Mail in soil test kits and nutrient management/fertilizer report

External links

• Ohio State University Extension Factsheet A List of Soil and Tissue Testing Labs and the Types of Materials Tested.
• UMass Testing Services and Price List
• Soil Testing Soil Investigation
• Guide to testing the Electrical Conductivity of soil water
• California Landscape Ordinance Soil Management Report California Assembly Bill 1881 – effective January 1, 2010 California Landscape Ordinance For Water Conservation and Water-use Efficiency | www.bettersoils.com
• http://www.willingtoncropservices.co.uk/soil-sampling-conventional-w-pattern.htm Willington Crop Services shows techniques used for soil sampling UK farm fields in conventional W pattern.
• http://www.mslanalysis.com Soil Testing Services
• http://www.smallholder-agriculture.co.uk/articles/how-to-get-the-best-out-of-your-soil-to-live-sustainably-11/ Importance of Soil Testing