A study was conducted at thirteen locations in North Dakota and Minnesota in 2013 and 2014 with the objectives of determining difference between the soil potassium (K) results based upon air-dried (KDry) and field-moist (KMoist) soil samples during the corn growing season and to evaluate corn response to applied K-fertilizer. Overall, KDry tests showed higher K levels in the soil test results compared to KMoist but the pattern of deviation was dependent upon various soil properties such as initial soil K level. Temporal variation of soil K levels indicated a need to consider time of soil sampling while making fertilizer recommendations. Potassium application significantly increased corn yields at only five out of 11 sites with soil K levels below critical K soil test levels (<150 ppm). Therefore, development of an improved soil testing strategy is required to improve the predictability of corn response to applied K fertilizer in this region.