Nitrogen Fixation Estimates for Some Native and Introduced Legumes, Forbs, and Shrubs

Abstract

Seedling plants of 16 legume, forb, and shrub species were compared with 2 alfalfa cultivars (Medicago sativa) for growth and survival in a nitrogen-free sand culture in the greenhouse. All seed accessions were inoculated with the same inoculum mixture. After 11 weeks all surviving plants were harvested and evaluated for top and root growth, percent nitrogen in roots and tops, and acetylene reduction rate of the root mass. All nonlegumes and several legumes died before the experiment was terminated at 11 weeks. Severe chlorosis and subsequent death appeared to be caused primarily from nitrogen deficiency. Six of the legume species-sainfoin (Onobrychis viciaefolia), black medic (Medicago lupulina), Medicago media, Phaseolus metcalfei, Vicia calcarata, and mesquite (Prosopus juliflora)-lived for 11 weeks and produced sufficient top and root growth and accumulated total nitrogen, indicating nitrogen was fixed in the root nodules. There were no differences among accessions for acetylene reduction rates in this experiment. Black medic produced as much or more top and root growth than the other species and merits additional study.