Performance of annual medics (Medicago spp.) as limited by moisture availability and grass competition in southern Arizona

I investigated whether rapid-maturing medics (genus Medicago) could establish and produce seed under the relatively dry winter conditions of southern Arizona. Hardseededness is common in many medics and may limit germination before fall rains. Therefore, I was also interested in the amount of medic germination that occurred following summer rainfall. Five accessions from four Medicago species (laciniata, polymorpha, truncatula and littoralis) were sown with or without a companion grass (Oryzopsis hymenoides) and grown with or without weekly 2 cm irrigation. While single-plant forage yields were over 8 times higher with irrigation, each accession established and produced up to 14 seeds for every seed sown under rainfed conditions. The companion grass had no influence on medic performance. Natural reestablishment occurred in all accessions from pods. Seedlings established in summer did not survive to flowering. M. littoralis appeared particularly well adapted to establishment under rainfed conditions in this environment. (Abstract shortened with permission of author.