Most of the soil nitrogen (N) is present in organic form, especially in the top 6 inches (75 – 95%), which is not readily available for plant uptake. Only about 0.1 – 0.3% is in inorganic or bioavailable forms such as nitrate and ammonium that plants can utilize. So, organic soil N is converted to inorganic forms for plants use, a process referred to as mineralization. The fraction of organic soil N that can be converted to inorganic form is referred to as potentially mineralizable N. Several factors including soil, previous crop, weather, and nitrogen management determine the extent of N mineralized. Nitrogen rate trials (>30) conducted over the past five years in West and Central TN suggested that mineralized soil N can contribute more than 20% of the total crop N requirements. Current N fertilizer recommendation for corn in Tennessee is based on realistic yield goals, which does not account for potentially mineralizable N that is available for the plant. Continue reading →

More recently, with emphasis on sustainable crop production, there are a number of tests that assess soil health. Some of the soil health tests such as the Haney Soil Health Tool (HSHT), which is adopted by USDA-NRCS, assess soil quality parameters as well as nutrient availability. The HSHT uses the H3A-4 extractant to estimate ‘plant available’ nutrients. The H3A-4 extractant simulates plant root environment by using organic acid plant exudates and has been touted as more representative of phosphorus availability. Some commercial soil testing laboratories offer HSHT and provide corresponding fertilizer recommendations. How does the test values and recommendations from H3A-4 relate to Mehlich-3 extraction? Publicly available information relating H3A-4 to Mehlich-3 extractable nutrients is limited. Continue reading →