| Abstract: | Abstract Alfalfa (Medicago sativa L.) does not grow as well as it used to in areas of Canada and northwestern United States. Affected plants have nitrogen (N)‐deficiency symptoms, few or no nodules, and respond to N fertilizer. For lack of a good explanation, such plants are called “sick”;. Six commercial inoculant products were tested with alfalfa grown on cores of eight soils in which alfalfa establishment and stand duration have been problems, to determine if inoculant quality influenced development of any sick‐alfalfa symptoms. Percentages of nodulated plants ranged from 35 to 82 after 5 to 8 weeks’ growth, and corresponded closely with estimated rhizobia numbers in the products. Dry forage yields were not closely related to percentage nodulation, however, because of residual soil N levels that supported seedling growth. Inoculant products containing inadequate numbers of rhizobia to promptly and effectively nodulate plants resulted in poor nodulation that may lead to establishment failure or sparse, weak stands. Contribution from the Central Oregon Exp. Stn. and Dep. of Microbiology, Oregon Agric. Exp. Stn. Journal Article No. 4910. |
