Dry bean (Phaseolus vulgaris L.) has the ability to form symbiotic relationships with N 2 -fixing bacteria. The research objectives were to evaluate yield and growth differences between dry bean cultivars from black, navy, and pinto market classes, with different N management combinations utilizing urea fertilizer, and two rhizobacteria inoculants. Research was conducted near Park River and Prosper, ND, during 2010, 2012. The experiment was a RCBD 3 × 2 × 3 factorial with four replicates with three dry bean cultivars, two N fertility levels, and two rhizobacteria inoculum sources plus a non-inoculated treatment. The pinto cultivar was also evaluated in 2014. Results showed significant cultivar main effect differences for nodules per plant, vigor, height, and 1000 seed weight. The pinto cultivar had significantly more nodules per root (19) compared with the black (13) and navy cultivars (9). There were not significant differences between inoculant treatments. The fertilizer main effect indicated significant differences for vigor and 1000 seed weight. No significant interactions were detected among factors. Addition of 56 kg N ha −1 resulted in more vigorous plants, but had no effect on seed yield, and reduced 1000 seed weight at harvest at Park River in 2013. Root nodule number was higher with the inoculant treatments with 16.2 and 15.8 nodules per plant compared to the non-inoculated treatment with 10.7 nodules per plant at Park River in 2013. The pinto variety Lariat with an application of 56 kg ha −1 had visually greener plants in 2013 and 2014, except Park River in 2013, but SPAD readings were not following the same trend. Inoculation and application of N fertilizer on dry bean may not be necessary if rhizobacteria are present and soil N levels are sufficiently high but future research on rates, timing, and N source and appropriate strains of Rhizobia inoculant on other pinto varieties is suggested.

BACKGROUND: Active optical crop sensors have been gaining importance to determine in-season nitrogen (N) fertilization requirements for on-the-go variable rate applications. Although most of these active in-field crop sensors have been evaluated in maize (Zea mays L.) and wheat (Triticum aestivum L. emend. Thell.), these sensors have not been evaluated in soybean [Glycine max (L.) Merr.] production systems in North Dakota, USA. Recent research from both South Dakota and North Dakota, USA indicate that in-season N application in soybean can increase soybean yield under certain conditions. RESULTS:The study revealed that OptRx™ sensor reading did not show any significant differences from early to midway through the growing season. The NDRE (normalized difference red edge) index data collected towards the end of the growing season showed significantly higher values for some of the N treatments as compared to others in both years. The NDRE values were strongly correlated to grain yield for both years under tiled (r = 0.923) and non-tiled (r = 0.901) drainage conditions. Certain soybean varieties displayed significantly higher NDRE values over both years. The three varieties tested across years, under both tiled and non-tiled conditions, showed a significant linear relationship between late August NDRE values and yield (R 2 = 0.85 for tiled and R 2 = 0.81 for non-tiled). CONCLUSION:In this research, the study results show that the OptRx™ sensor has the potential to work for soybean as well, though later in the crop growing season. Further investigation is needed to confirm the use of OptRx™ sensor for variable rate in-season N applications in soybeans.