Soil Test

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.

Labs, such as those at Iowa State and Colorado State University, recommend that a soil test contains between 10-20 samples for every 40 acres (160,000 m2) of field. Tap water or chemicals could change the composition of the soil, and may need to be tested separately. 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 is a method used to create an "average sample" or "composite sample." It is a common procedure and it must be used judiciously or it can artificially dilute the quantities and the concentration of the sample, causing the sample to fail the government agency requirements for sampling. A reference map can be created to help keep more accurate and detailed records that indicate the location and quantity of samples that were taken in the field - considerations that affect the interpretation of test results.