Potassium (K) can be a major yield limiting factor in corn production in Minnesota. Soils across Minnesota vary in their K holding capacity and their ability to supply K to the corn crop. Much of the variation in K cycling is due to clay types and other mineralogical properties of the soil. A detailed survey of soil mineralogy will be conducted to better understand how K cycles in Minnesota soils with and without K response trials. In addition, research from sandy soils has shown a lower K requirement then what is currently suggested. While the over application of K does not present significant environmental risks, applying K that is not needed to soils with a low holding capacity for K does not make financial sense. Recent data showing less K required on sandy soils demonstrates a need to look more closely at cycling of K, including K weathering and pH impact on soil K holding capacity, for irrigated sandy soils. The overall goal of this research will be to provide a better basic understanding of K in Minnesota soils in order to provide a better site specific set of K fertilizer guidelines for corn production in Minnesota factoring in soil chemical properties. Data collected can be used for the development of online assessment tools for K as well as P to help corn producers decide the best options for fertility management on their fields.