Reimplementation of Moist Soil Testing to Improve the Assessment of Crop-Available Potassium in Iowa Soils

Since 1989 and until the summer of 2012 all soil testing laboratories in Iowa and the USA dried soil samples at 35 to 40 oC (95 to 104 oF) before soil analysis for potassium (K), phosphorus (P), and other nutrients. Since last fall, however, a laboratory that began operations in Iowa is using testing procedures that involve no soil sample drying, and another laboratory is offering moist soil testing in addition to the commonly used test based on dried samples. These laboratories are using a moist soil sample handling procedure that the Iowa State University (ISU) Soil and Plant Analysis Laboratory used from 1963 to 1988, and which was among methods recommended by the North-Central Regional Committee for Soil Testing and Plant Analysis (NCERA-13) committee during the 1980s (Eik et al., 1980; Eik and Gelderman, 1988). The re-implementation of the moist test by these laboratories and last fall update of the NCERA-13 sample preparation chapter to again include the moist sample handling procedure (Gelderman and Mallarino, 2012) have generated many questions.