Ask for these items at your local University Extension center. When to sample Nutrient levels usually vary only slightly from season to season. Soil sampling just after harvest of a high-yielding corn or soybean crop usually results in a slight depression of exchangeable potassium compared to later fall, winter or spring sampling. Most people take soil samples in spring, just before applying fertilizer. That leaves little planning time for important fertilizer and limestone application decisions.
Spring is also the time when soil testing laboratories are overloaded with samples.
This will delay the return of results. Fall and winter sampling leaves more time for planning limestone and fertilizer programs for the coming year. Collecting the soil sample Sample from relatively uniform areas of a field. Map the fields or obtain field maps from your county's soil survey or ASCS office. Carefully delineate any known differences in soil nutrient composition.