On-Farm Approach to Measure Biological Nitrogen Fixation in Soybeans.

Currently, there is knowledge gap on soybean biological N fixation (BNF) information and its relationship with soil-weather-and other plant characteristics in order to identify potential scenarios in which BNF could be the main limiting factor blocking soybean yield potential. Soybean production heavily depends on the total nitrogen (N) uptake primarily supplied via BNF process. New on-farm BNF procedure was investigated in order to perform determination of ureide methodology (in-field testing). This BNF methodology will be calibrated under field conditions utilizing the 15-N natural abundance technique. The objective of this research study was to quantify BNF on soybeans in a greenhouse setting utilizing three fertilizer N rates. The ureide method was tested in different plant organs: base of the stem (5-inch), rest of the stem, petiole of the upper plant trifoliate, and the upper plant trifoliate. Both ureides and nitrate concentrations were determined in the plant tissues in order to estimate the relative ureide abundance (RAU). The RAU was utilized as a tool to predict the BNF status of the soybean crop. In-depth characterization of soybean N systems will permit a better estimation of N budgets, acting as indicators of productive and sustainable soybean farming systems.