Take a good soil sample to help make good decisions

By Dave Nicolai, University of Minnesota Extension

Soil tests can be no better than the sample. Therefore, proper collection of the soil sample is extremely important.

< Divide the field into uniform areas.
Each area should have the same soil color and texture, cropping history, and fertilizer, lime and manure treatments. The use of soil survey maps that indicate soil types, slope phase and erosion phase are useful because organic matter, nutrient levels and soil pH can vary following these map units. One sample should not represent more than 20 acres on level, uniform landscapes, or five acres on hilly or rolling land. Soil sampling using an intensive grid pattern of at least 2 1/2 acres in size is another option for growers working with a crop consultant or agriculture professional.

< Sample each area for composite samples.
Within each area collect 15 to 30 subsamples (cores, borings or spade slices) in a zig-zag pattern throughout the designated field area. The more variable the soil, the more subsamples should be combined per area sampled. Scrape off all surface residue from the subsample site. Sample to a depth of 6 to 8 inches (plow layer) for cultivated crops, or three inches for pasture or sod fields. Sample row crop fields between rows, except for ridgetill plantings. Where ridgetill is used, take the sample to a depth of 6 to 8 inches on the shoulder of the ridge, avoiding the starter fertilizer band. Also avoid sampling dead or back furrows, terraces, old fence rows, lime or fertilizer spill areas, headlands, eroded knolls, low spots or small saline areas. Sample at least 300 feet away from gravel or crushed limestone roads because their dust changes soil pH.

< Mix the subsamples.
Mix the subsamples thoroughly in a clean plastic pail, and fill the sample box or bag to the fill line (1 pint). If the samples must be taken wet, they should be dried before being mixed and submitted to the laboratory.