In agriculture, a soil test is the analysis of a soil sample to determine nutrient and contaminant content, composition and other characteristics such as acidity or pH level. Tests are usually performed to measure the expected growth potential of a soil. A Soil test measures fertility, indicates deficiencies that need to be remedied and determines 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.
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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. Tap water or chemicals could change the composition of the soil, and may need to be tested separately.
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 a factor for various nutrients, and other soil components vary during the year, so sample timing may also affect results. Usually the best time when soil tests can be done is spring. 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/concentration, 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.
Soil chemistry changes over time as biological and chemical process break down or combine compounds over time. These processes change once the soil is removed from its natural ecosystem (flora and fauna that penetrate the sampled area) and environment (temperature, moisture, and solar light/radiation cycles). As a result, the chemical composition analysis accuracy can be improved if the soil is analyzed soon after extraction--usually within 24 hours. The chemical changes in the soil can be slowed during storage and transportation by freezing it. Longer term soil sample preservation (many months) can be accomplished by air drying.
Soil testing is often performed by commercial labs that offer a variety of tests targeting groups of compounds and minerals. There may be some advantage to using a local lab that is familiar with the chemistry of the soil in the area where the sample was taken. This enables technicians to recommend the tests most likely to reveal useful information.
Laboratory tests often check for plant nutrients in 3 categories:
Do-it-yourself kits usually only test for the three "major nutrients" and for soil acidity or pH level. Do-it-yourself kits are often sold at farming cooperatives, university labs, private labs, and some hardware and gardening stores. Electrical meters that measure pH, water content, and sometimes nutrient content of the soil are also available at many hardware stores. Laboratory tests are more accurate than tests with do-it-yourself kits and electrical meters. Here is an example soil sample report from one laboratory.
Soil testing is used to facilitate fertilizer composition and dosage selection for land employed in both agricultural and horticultural industries.
Prepaid mail-in kits for soil and ground water testing are available to facilitate the packaging and delivery of samples to a laboratory. Similarly, in 2004, laboratories began providing fertilizer recommendations along with the soil composition report.
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.
Lead is a particularly dangerous soil component. The following table from UMinn categorizes typical soil concentration levels and their associated health risks.
| 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 |
Six Gardening Practices to Reduce the Lead Risk
Some laboratories analyze for all 14 mineral nutrients and a dozen non-essential, potentially toxic minerals utilizing the “universal soil extractant” (ammonium bicarbonate DTPA) reference.
RECORD TEST: Record test means the tests of soil/murum taken for disturbed & undisturbed samples. Record tests are taken only in soil testing laboratory.
Following are the tests ( Record) taken for soil:
Following are the tests ( Record) taken for murum:
Shear test are taken on two machines.
Small shear machine- Small shear machine is used for hearting material & for casing material if particle size is less than 4.75mm.
Large shear machine – Large shear machine is used for casing material if particle size is more than 4.75mm.
Permeability test:- For Hearting material Permeability lies between 10-6 to 10-7
Permeability test:- For Casing material Permeability lies between 10-4 to 10-5
Common mineral soil contaminants include:
-- Soil Testing --
--Soil Contaminants --