Wednesday, November 15, 2006

Annual Medics (Medicago spp.) Response to Rhizobia Inoculation.

Jacob Bushong, Twain Butler, Anowarul Islam, and Matt Rowland. The Samuel Roberts Noble Foundation, 2715 Chattanooga Loop #205, Ardmore, OK 73401

Medics have the potential to increase forage production in the Southern Great Plains.  The objective of this study was to determine the optimal rhizobia strain to maximize yield.  Eight medic species (M. orbicularis, M. lupulina, M. polymorpha, M. rigidula, M. rigiduloides, M. minima, M. arabica, and M. truncatula) and five rhizobia strains (Nitragin N, WSM1115, M2, M49, and Dormal alfalfa) were utilized.  In the field study there was no difference in  yields between inoculants at 110, 150, and 200 DAE for all species.  M. rigidula displayed the highest yield with 4848 kg ha-1 dry matter produced.  This was followed by M. polymorpha, M. rigiduloides, M. lupulina, M. minima, and M. orbicularis.   No significant effects in nodule counts were observed at any of the harvest dates.  The M. rigiduloides displayed little nodulation with less than 1 nodule per plant at 200 DAE.  Visually the M. rigiduloides displayed chlorotic leaves in all plots except those receiving N fertilizer.  In the greenhouse study the Medicago specific strain from Nitragin yielded the highest number of nodules per plant for M. polymorpha, M. rigiduloides, M. arabica, M. minima, and M. rigidula, however, most of these strains were not statistically different from others.   The M2 strain had the highest nodule counts per plant for M. lupulina, while the M 49 strain had the highest counts for M. orbicularis.  The nodules on the greenhouse plants were also white in color, meaning they were not actively fixing N, and it was not known if they were beneficial or parasitic.  Because of this, future research will be conducted studying nodulation and plant biomass beyond 30 DAE.  In conclusion, inoculation may be beneficial the first year of planting medics, however, more research will need to be conducted on identifying the specific strains of rhizobia needed by individual species.