Survival of Rhizobium leguminosarum in soil after addition as inoculant

Summary

Three streptomycin-resistant (str^r) strains of the root-nodule bacteria Rhizobium leguminosarum biovar viceae were added to a field soil harbouring an indigenous population of R. leguminosarum. Three or 4 years later more than 10⁴ bacteria remained per gram of soil. The size of the str^r population decreased with time, its ‘half-life’ ranged between 1.2 and 2.1. years. The survival was positively influenced by host-legume, non-host-legume and non-legume crops. The highest and lowest survival rates were found in soils cropped with a host legume every year, and in soil kept fallow, respectively. The percentage of nodules on pea plants (Pisum sativum L.) occupied by the str^r rhizobia decreased during the 3- or 4-year period following the introduction of the str^r rhizobia to the soil.

Rhizobium leguminosarum, Soil, Survival