Dry K and Wet K Soil Testing Methods
The re-emergence of an old soil testing concept has received considerable attention over the past year. It raises the question, which is a more accurate potassium predictor: drying the soil for processing or using the field moist
The moist process was developed at Iowa State University over 50 years ago. The general observation is that drying soil artificially, a process promoted by commercial laboratories to ensure homogenization of a soil sample, raises the measured potassium (K) levels and subsequently leads to lower fertilizer recommendations. The degree of disparity between a Wet K (analysis of an as-received soil sample) and a Dry K (standard dried-and-ground processing) is variable with factors including, (1) soil type, (2) heat of drying and (3) native K abundance.
These variables lead to a poor correlation between Wet and Dry K results, such that, a general correction factor could not be successfully applied to reconcile the two values. Current emphasis focuses on soil K levels in Iowa where the average K levels have been declining for several years. The Wet K test is being promoted as a solution to this concern; however, data trials must be ran to understand more precisely the mechanism of difference.
It is AgSource's approach that both test methods provide valuable data for making fertilizer management decisions. Click on the list at the top of this page for additional information. Contact AgSource today with any further questions about potassium analysis.
Seasonal variables in potassium testing: http://fyi.uwex.edu/discoveryfarms/files/2011/06/Laboski-k-variability.pdf
Reasons for soil test potassium variation: http://www.agronext.iastate.edu/soilfertility/info/NCSFC%202011%20Mallarino%20p65.pdf