LONG-TERM FIELD-STUDY SHOWS INCREASED BIOMASS PRODUCTION IN TREE LEGUMES INOCULATED WITH RHIZOBIUM

Nodulation potential, nitrogen fixation efficiency (nitrogenase activi ty) and biomass yield response of Leucaena leucocephala and Acacia nil otica to inoculation with 6 selected fast growing Rhizobium strains wa s explored in long-term (5 year) field trials. All the strains formed nodules and fixed nitrogen in L. leucocephala and A. nilotica. Seasona l effects on nitrogenase activity was observed and in winter (ambient temperature about 20 degrees C), nitrogenase activity could not be det ected. However, with the onset of spring and a rise in temperature, fr esh nodulation (renodulation) by all the inoculant rhizobial strains w as observed in both the tree legumes. In L. leucocephala, maximum reno dulation was exhibited by strain Al while in A. nilotica, strain AB3 f ormed the maximum renodulation 24 months after transplantation. Dry ma tter yield of all the inoculated plants demonstrated a significant inc rease over that of the uninoculated plants at the end of five years af ter transplanting. In L. leucocephala, strain NGR8 gave the maximum re sponse (45% more dry matter yield) in dry matter production while in A . nilotica, strain USDA 3325 showed a 25% increase in total dry matter yield five years after transplantation.