Sampling your soil for better soil test results
Soil sampling is not rocket science, but taking certain steps can result in more useful and accurate soil test results.
Sampling your soils to determine soil pH and soil nutrient levels is an excellent management tool that aids in determining not only liming requirements, but also your fertilizer needs.
Soil sampling may be conducted any time of the year with a few exceptions. First, sampling should be done prior to lime or fertilizer applications as these nutrient inputs will directly affect the accuracy of your testing results. If either lime or fertilizer has been applied, wait a period of time to allow for the nutrient applications to equilibrate in the soil before sampling and testing.
The frequency in which you should sample your soils also varies depending on factors such as the crops grown, crop rotations, nutrient inputs and removals, soil texture and a pre-existing soil test history. A general rule of thumb when it comes to soil sampling frequency is to follow your crop rotation frequency. For example, if you have a three-year crop rotation, sample your soils every three years. If you have a four-year crop rotation, sample every four years. Remember, the more consistent you are in following your crop rotation frequency and taking samples during the same time each year, the more comparable the soil test results will be.
When it comes to taking your soil sample, the key is to obtain a sample that is representative of the area. For traditional soil sampling, a single sample should represent no more than 20 acres. Each soil sample should comprise of at least 15 to 20 soil cores to a depth of 8 inches which have been collected from the field in a random zig-zag fashion. If you have a large field, you will need to take multiple soil samples that represent a portion of the field. Splitting your field according to good versus bad production areas, old use patterns, soil types, and other influential factors will yield more representative soil test samples.
Additionally, there are other soil sampling strategies that are more intensive than traditional sampling, such as using GPS technology. For additional information on these sampling strategies or soil sampling and testing, see MSU Extension Bulletin E-498, Sampling Soils for Fertilizer and Lime Recommendations, and Extension Bulletin E-498S, Sampling Soils for Fertilizer and Lime Recommendations: Frequency of Soil Sampling.