Nitrogen flows from the roots of soybeans to the tops mostly as nitrate (from the soil solution) and compounds known as ureides (the export product of nitrogen fixation from the nodules). The concentration of ureides in the plant is directly related to the number and vigor of the nodules. In our laboratory, we have developed a simple and direct method of analyzing soybean tissues for ureide content. It is our hope that this test might someday be offered by soil and plant testing labs, but more field calibration data are needed. The purpose of this proposal is to conduct inoculation studies in the field, and relate the response (yield, protein content) to the ureide levels in the plants...