Making P and K fertilizer recommendations
click image to zoom Critical levels and Maintenance Limits for potassium is defined in the Tri-state Fertilizer Recommendations based on CEC (Cation Exchange Capacity) of the soil and are shown in Table 1.
Three publications that can help farmers looking to develop fertilizer recommendations are:
The Fertilizer Recommendations for Corn, Soybeans, Wheat and Alfalfa can be found at http://agcrops.osu.edu/specialists/fertility/fertility-fact-sheets-and-bulletins/tri_state_recs.pdf
Developing Phosphorus and Potassium Recommendations for Field Crops (AGF-515-12) walks through developing a nutrient recommendation and how much fertilizer is needed to meet that need found at http://agcrops.osu.edu/specialists/fertility/fertility-fact-sheets-and-bulletins/tri_state_recs.pdf
An Excel Spreadsheet to calculate P, K and Lime Recommendations (Beta Version-11/2012) for 7 fields or zones and a three crop rotation can be found at http://agcrops.osu.edu/specialists/fertility/fertility-fact-sheets-and-bulletins/TriState.xlsm
Other helpful nutrient related publications can be found at http://agcrops.osu.edu/specialists/fertility/fertility-fact-sheets-and-bulletins