Nitrogen effect on Nodulation of Alfalfa (Medicago sativa L.) and Sainfoin (Onobrychis vicilifolia Scop.)

Biological Nitrogen fixation is one of the two sources of nitrogen (N). Most nitrogen fixation in agriculture takes place in the Fabaceae family which can form symbiotic relationships with Rhizobium spp. if it is present in the soil. This study reexamines the effect that nitrogen (N) application has on nodulation number on the rooting zone of two small seeded legumes, alfalfa (Medicago sativa L.) and sainfoin (Onobrychis vicilifolia Scop.) at three different rates. Plants were grown using USU's nutrient solution with an initial N concentration of 1mM to jumpstart the plants. At day 14 the plants were received the appropriate concentration of N, that being 0, 1, or 10 mM. Each pot was reduced from six to three plants to prevent competition effects from other plants being too great. Plants were harvested at day 32. Wet and dry weights and nodule counts were taken to measure plant performance. The nodule data showed that there was a difference in the different treatments. There was a strong suggestion that N rate affected the nodulation of each plant species differently, but that N concentration by itself did not have a significant effect overall. Alfalfa nodulation showed the greatest negative response to N concentration with the highest nodule counts being recorded in the 0 mM treatment and the highest nodule counts of the experiment. Sainfoin had the highest nodule count at the 1 mM concentration. Both legume plants had mostly white and immature nodules at the time of harvest. Observations were consistent with past literature, especially sainfoin. a replicate of sainfoin with 0 mM N did not nodulate. Alfalfa plants at the highest N concentration showed drought stress symptoms which decreased overall plant size. These factors could have caused a confounding effect to the results. This study should be repeated with more N treatment levels to verify plant response and study results.