Correlating a Ureide Tissue Test for Soybean with Field Inoculation Studies.

Nitrogen requirements for soybean (Glycine Max L. [Merr.]) are usually provided via the symbiosis with Bradyrhizobium sp. Nitrogen flows from the roots of soybeans to the above ground biomass in the form of nitrate from the soil solution or from ureides created in nodules.  The concentration of ureide-N in the plant is directly related to the activity of N fixation in the nodules.  A new method to analyze ureides was recently developed. The objective of the study was to provide field calibration of the ureide test as an indicator of adequacy of N fixation in soybean.  Field inoculant studies were conducted in 2007, 2015, and 2016 in Carrington and Minot, ND using different inoculation methods. The studies were conducted in soils with no history, or a limited history, of soybean production. Counts of nodule-forming bacteria in soil at planting suggest that numbers greater than 100 g^-1 of soil are associated with adequate N fixation without inoculation and counts less than 100 g^-1 of soil are associated with a significant plant response to seed inoculation. A preliminary critical level of ~1500 ppm of ureide-N in the plant axes (stems plus petioles) at the R1 growth stage is currently suggested in order to meet plant N requirements. At some sites, with no history of soybean production, the highest yield and protein were observed when seed was inoculated with two different forms of bacteria. The 2016 field trials are in progress and results from these trials will be presented.

Correlating a Ureide Tissue Test for Soybean with Field Inoculation Studies