Soybean Nodulation and Plant Response to Nitrogen and Sulfur Fertilization in the Northern US

Soybean [Glycine max (L.) Merrill] seed yields in the northern United States may increase with the application of fertilizers;however Nitrogen (N) may decrease root nodulation. This study was conducted to understand the impact of N and sulfur (S) fertilization on soybean nodulation, plant, shoot and root biomass. Two cultivars were planted in experiments across ten site-years during 2015-2016. Plant observations took place at the V4 and R4 soybean growth stages. There were 41% more nodules per plant at R4 compared to V4 (38.3 vs 27.2 nodules, respectively). Cultivars responded differently to N and S fertilizer. The nodules per plant between the cultivars (30.3 vs 24.4) were different as well as the percent medium and large-sized nodules, which indicates the need to evaluate additional genotypes. Adding N decreased root nodulation (from 31.8 to 23.7 nodules per plant) and decreased nodule size but had no effect on plant, shoot or root mass. Averaged across N rates total plant mass was 2.26 and 11.36 g per plant at V4 and R4, respectively. Shoot mass, average across N rates was 1.77 and 9.65 g per plant at V4 and R4, respectively, and root mass, average across N rates was 0.49 and 1.71 g per plant at V4 and R4, respectively. Sulfur did not have an effect on nodules per plant but increased the percent medium size nodules at the R4 observation. There was no N by S interaction observed for nodule number, size of the nodules, and plant, root and shoot mass. As cultivars differed in their nodulation response to N and S, additional research would be helpful to screen other cultivars.

Tile Drainage and Nitrogen Fertilizer Management Influences on Nitrogen Availability, Losses, and Crop Yields

Installing tile drainage facilitates early planting and field operations, and tiling has tremendously increased in the Red River Valley (RRV) due to recent wet cycles. This experiment studied tile drainage and N-fertilizer management effects on N availability, N losses, and yields of corn (Zea mays L.) and sugarbeet (Beta vulgaris L.) in a naturally poorly-drained Fargo soil during the 2012-2013 growing seasons. Regardless of drainage, applying 146 kg N ha-1 with nitrapyrin resulted similar soil N availability to 180 kg N ha-1 without nitrapyrin in sugarbeet in both years. In corn, application of nitrapyrin resulted either higher or similar soil N levels to split-N application. In 2013, application of urea alone increased soil N availability during the early corn growing season under the undrained condition, whereas nitrapyrin delayed N release in the tile-drained soils. Corn and sugarbeet yields averaged 7.4 and 47.0 Mg·ha-1 in 2012, and averaged 8.3 and 38.3 Mg·ha-1 in 2013, respectively, with no significant differences among N-sources. However, corn yield increased on an average by 27.6% with N-fertilizer application over unfertilized control in 2013. In 2012, sugarbeet root impurity (% sucrose loss to molasses) increased by 13.8% and 17.2% with 146 kg N ha-1 plus nitrapyrin and 180 kg N ha-1 treatments, respectively, compared to unfertilized control. Besides, higher N rates were usually associated with greater daily soil N2O emissions, with the maximum flux of 105 g N2O-N ha-1·d-1 recorded under corn. Addition of fertilizer-N increased NH3 volatilization losses up to 1.9% and 0.5% of the applied-N in corn and sugarbeet, respectively. Tile drainage influenced soil N availability more than crop yield during two years of study. Nitrogen management can have pronounced effects on N availability and losses. A long-term study is needed to investigate the fertilizer-N use efficiency of crops under tile drainage condition.

Nitrogen Fertilization and Inoculation Effects on Dry Bean

Dry bean (Phaseolus vulgaris L.) has the ability to form symbiotic relationships with N2-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, 2013. 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.