Reevaluating the University of Kentucky's Soil Fertility Recommendations for Soybean Production

The land grant university Cooperative Extension Services (CES) developed crop soil fertility recommendations with correlation (crop productivity/quality versus soil test) and calibration (crop productivity/quality versus nutrient application rate -- at different soil test levels) field studies. Soil test potassium (STK) values have decreased with time across Kentucky, according to data generated from the University of Kentucky Regulatory Services Soil Test Lab. Further, the majority of soybean samples submitted to the UK Plant Diagnostic Center at Princeton diagnosed with nutrient deficiency are low in K. Whether producers are applying less K than recommended or the recommended rate is not sufficient to maintain STK levels is unknown. Soil phosphorus (P) levels do not appear to be declining at the same rate as STK, but these are falling in some areas. Additionally, the use of early (and often) in-season plant analysis and/or crop canopy sensors to better detect soybean nutrient stress has been proposed. We hypothesize that higher current nutrient removal rates are not being addressed with current fertilizer rate recommendations. We propose to test the adequacy of current UK Cooperative Extension Recommendations in a field with low soil test P and K values. We also propose to evaluate the use of early/often plant tissue analysis and crop sensor technology throughout the growing season to detect soybean nutrition stress. Soybean yield and nutrient removal will be determined in our final evaluation of the several soil fertility programs we examine. An economic analysis of the project will be conducted in order to provide a better understanding of the costs associated with and possible economic repercussions associated with over or under fertilizing.