Pigeonpea (Cajanus cajan L. Millsp.) germination under in vitro conditions was reduced beyond pH 8.8, whereas, its rhizobia could grow up to pH 11.5. In the field, growth of and uptake of N by perennial pigeonpea were drastically reduced beyond soil pH 8.4, but increasing alkalinity did not affect N content of leaf or stem. In a greenhouse study on reclaimed alkali soil, there was good nodulation in control. Rhizobium inoculation improved root biomass and N content. Perennial pigeonpea had more root biomass and better nodulation than an annual species. Results point to the importance of studying root effects when inoculation effects are not apparent on shoot biomass.
Agroforestry, nodulation, nitrogen fixation, perennial pigeonpea, Rhizobium biofertilizer, root biomass, soil alkalinity/sodicity
