Soil test calibration research conducted by Dr. Antonio Mallarino with the Department of Agronomy at Iowa State University has produced new data for potassium (K). According to Dr. Scott Murrell, for soil tests to have meaning, they must be calibrated to yield response. Much of the calibration data for soybeans was collected decades ago, when varieties, tillage and other management practices were much different than they are today. Using outdated interpretations of soil test levels can lead to misapplications of nutrients for current and future soybean production. Consequently, the need for updated information is ever-present.
Dr. Mallarino has obtained new soil test calibration data for K and has shown that higher soil test K levels are needed for economically optimum soybean production. In addition, K applied in bands in reduced tillage systems has produced superior soybean yields compared with the traditionally used broadcast applications. An investigation into soil test procedures has revealed that new P detection methods used by many labs may lead to higher target soil test levels for soybean production.