Common sources of contamination include dirty sampling tools, storage vessels and surfaces on which soils are spread to dry. Ashes from tobacco products can cause considerable contamination of soil samples. Soils should be shipped to the testing laboratory only in containers approved by the lab. Individual cores should be mixed thoroughly to form a composite sample. After drying, a sub-sample of appropriate size should be taken from the composite mixture and sent to the testing laboratory for analysis.
Several tests are available to measure the availability of individual nutrients in the soil.
The recommendations made here are based on research conducted using very specific tests, which are identified for each nutrient. Producers and consultants should always be certain their fertilizer recommendations are based on research using the same procedures used to generate their soil test results. Other procedures may yield results incompatible with the recommendations given here. The change to ppm is being made because it more truly represents what is measured in the soil. Soil test values are an index of availability and do not reflect the total amount of available nutrients in soil.