Number and effectiveness of cowpea rhizobia in soils of Guyana

Abstract

Soils in 15 fields in Guyana were sampled to determine the population size of cowpea rhizobia present and their effectiveness. The population size was influenced by the presence of cowpea in the cropping sequence and ranged from < 1 to 10º rhizobia gram-1 of soil. Most of the fields contained approximately 200 rhizobia g-1. A total of 65 rhizobial isolates were tested for effectiveness and most were only moderately effective and ? 20% were ineffective. The results indicate that the indigenous cowpea rhizobial populations are low enough in number and effectiveness for a potential response to inoculation of cowpeas grown in Guyana.