Many nutrients and lime are not mobile in the soil. When applied to the soil surface without tillage, these materials remain in the top 2 inches, especially in production systems that lack tillage. If a soil sample is taken at a standard 8-inch depth, the top 1 to 2 inches, which have higher nutrient concentrations, will be mixed with the lower 6 to 7 inches, which have lower nutrient concentrations. Surface-applied nutrients that are not mixed will likely not be measured. In addition, continued application of ammonium-N and subsequent nitrification acidifies the surface soil. Therefore, soil collected from several depths should be used to evaluate surface and below-surface conditions.