Survival and efficiency of nitrogen fixing bacteria when introduced in Jamaican and mid-Missouri soils

Much progress has been made in identification and isolation of effective competitive rhizobia strains. However, insufficient literature is available on the testing of these strains under field conditions in tropical soils, where they are needed most. A research project to provide information on the competitiveness and survivability of certain introduced rhizobia strains was initiated in 1985 in Jamaica. Field experiments utilizing four locations, two cowpea cultivars (Vita 3 and Mississippi Silver) and four rhizobia strains (JRC 29, IRC 26, IRC 503B, and 32 H1) were conducted each of the three years from 1985-1987. The inoculum strains JRC 29 and 32 H1 formed the majority of the nodules in the first year. This number declined in the second and third year. However, nodule occupancy for these strains (JRC 29 and 32 H1) was much higher than was reported for other strains in similar studies. During the third year (1987) of the study the strains JRC 29 and 32 H1 showed nodule occupancy averaging 80 and 65.5% respectively, at all locations. Strains IRC 26 and IRC 503B exhibited an average nodule occupancy of 17.4 and 21.6%, respectively, at the same locations. The reaction of cowpea cultivars to inocula, were similar when growth and development were measured. However, "Mississippi Silver" had higher grain yields than "Vita 3." Rhizobium strains varied in their ability to survive and influence crop growth at the different locations. Maximum growth and development were obtained by both cultivars when the Rhizobium JRC 29 and 32 H1 were used. Our results demonstrated that the native strain JRC 29 survived much better than the introduced strains of IRC 26 and IRC 503B. In most locations, the competitiveness and survival of 32 H1 were comparable to that of JRC 29. (Author abstract)