New Method to Determine Potentially Mineralizable Nitrogen in Agricultural Soils.

Current methods to quantify potentially mineralizable N, including the Illinois Soil N test (ISNT) and Direct Steam Distillation (DSD) have shown the potential to predict N fertilizer rates for rice (Oryza sativa L.), but have shown mixed results for upland crops such as wheat (Triticum aestivum) and corn (Zea mays). These methods use various forms of reagents, reaction times and separation techniques but measure alkaline hydrolyzable-N which is restricted to NH₄-N, and a portion of the amino acids and amino sugars contained in the soil. One potential issue restricting the adoption of these methods for predicting N fertilizer needs for upland crops is their inability to quantify soil NO₃-N, which would require a second analytical technique and is immediately plant available. Although the ISNT and DSD provide reliable results, they can be time consuming and/or require caustic chemicals that can be costly at the concentrations required for the analysis. These limitations have led to the development of a new method to quantify amino acids and amino sugars from soil extracts that can also be used to quantify NH₄-N and NO₃-N, thus providing an accurate estimate of immediately plant available-N and potentially mineralizable-N. Initial results indicate that the amino acids and amino sugars quantified from the extract analysis correlates well with alkaline hydrolyzable-N methods, but at a much lower concentration. The new method also has been calibrated to predict N rates for rice and is currently being investigated for corn. The primary limitation of the new method is the extraction step that has been added. Although this step is an extra requirement above current alkaline hydrolyzable-N methods, it allows for the quantification of NO₃-N which is important for upland crop production systems. This new method has wide adaptability that reduces cost and labor requirements while adding a better estimation of N availability.