Evaluating soil nutrients and pH by depth in situations of limited or no tillage in western Oregon

Abstract

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.