Iowa State University Extension and Outreach Field Agronomists have completed their fall survey of subsoil moisture in northwest Iowa. Subsoil moisture sampling in Iowa dates back to February 1954 when ten sites were chosen for soil moisture sampling. In 1959, the sampling increased to 22 locations, and in 1971, 61 locations were sampled. Today, 18 locations are sampled in northwest Iowa.

Soil testing is an essential tool for managing phosphorus (P), potassium (K) and other nutrients. In Iowa and many states, the units reported in a soil test are expressed in parts per million (ppm) of the elements (not oxides P₂O₅ or K₂O, as in fertilizers) of dry or moist soil depending on the test. Different test methods can be used for a specific nutrient.