SPREAD OF RHIZOBIUM AND BRADYRHIZOBIUM IN SOIL

Movement of Rhizobium loti and Bradyrhizobiwn sp., from established Lotus corniculatus and L. pedunculatus respectively, was studied to determine if lack of root-nodule bacteria would limit nodulation following natural reseeding. High populations of root-nodule bacteria occurred in the soil under established plants. However, movement away from established plants varied with topography. Downslope movement was most rapid, but did not exceed 4.0 m yr-1. Lateral movement was very low at < 0.25 m yr-1. Few root-nodule bacteria were detected even 1 m upslope from established plants 5 yr after sowing, indicating little movement in wind-blown dust or on the hooves of grazing animals. When assessing the feasibility of natural reseeding, maximum rates of spread of root nodule bacteria of < 0.25 and 4.0 m yr-1 laterally and downslope respectively should be expected.