Movement of Rhizobia between Alfalfa Plants

Abstract

AbstractEvidence on the rapidity of movement of rhizobia in the soil is inconclusive. Successful inoculation of most of the legume plants in a field would result in subsequent inoculation of the remaining plants if substantial movement of legume bacteria occurred. The objective of this study was to determine the distance rhizobia move in the soil between inoculated and noninoculated alfalfa (Medicago sativa L.) plants during the seeding year. Three field experiments were conducted in North Carolina. Experiments 1 and 2 were established on a Norfolk sandy loam (fine‐loamy, siliceous thermic Typic Paleudult) and Exp. 3 on an Appling sandy loam (kaolinitic thermic Typic Hapludult). Alternating rows of inoculated and noninoculated alfalfa (subplots) were seeded at spacings of 15,30 and 60 cm (whole plots) in four replications. Periodic measurements of nodulation, color, height of top growth and N concentration of top growth and roots were made. Results indicated that the lateral movement of rhizobia in an 11‐month period was largely limited to a distance of 15 cm. There was evidence that substantial N was obtained by noninoculated alfalfa rows from adjacent inoculated (15‐cm spacing) rows by sloughing and/or excretion.