Rhizosphere can enhance effectiveness of rhizobia

Abstract

Annual legumes are usually inoculated with rhizobia annually to ensure high nodulation, nitrogen fixation and crop yields. To assess the potential of establishing a highly effective population of soil rhizobia in a crop preceding the legume, the effect of passing the rhizobia through crop rhizosphere prior to planting peas was investigated in pot experiments. We inoculated pea seeds with soil obtained from (a) the rhizosphere of peas or wheat with or without rhizobial inoculation, and grown in potted soil, or (b) inoculated and uninoculated soil-only control pots (non-rhizosphere). Seeds and soil had been inoculated with Rhizobium leguminosarum bv. viceae strain NRG480 (also known as 128C56G, LiphaTech, Milwaukee, WI). Inoculation of peas with previously-inoculated soil sampled from wheat rhizosphere nor pea rhizosphere had no significant effect on nodulation and plant dry matter (DM) of peas. However, inoculating peas with previously-uninoculated soil (i.e., indigenous rhizobia) sampled from pea rhizosphere significantly increased pea nodule and shoot DM. Although wheat rhizosphere did not affect nodulation and nitrogen fixation by pea rhizobia, it supported a large population of inoculated Rhizobium. These results indicate the possibility of establishing a large population of Rhizobium for a legume crop by inoculating the preceding cereal crop in a rotation.