Inoculated Legumes and Revegetation/Roadside Plantings

Project summary:

This study builds on earlier work to identify inoculant-quality rhizobia and inoculation practices for mixed prairie legumes used in revegetation and roadside plantings. It examines the benefits from inoculation for the legumes used in such plantings, and how inoculation in the prairie setting influences nodulation, nitrogen fixation and growth of both legume species and non-legumes. It also examines how inoculation influences mycorrhizae and other beneficial rhizosphere organisms. Specific objectives include: (1) to evaluate the role of inoculated legumes in the productivity and health of revegetated and roadside plantings; and, (2) to study population changes over time among the organisms associated with inoculated and uninoculated prairie legumes in roadside and revegetation plantings.

Prairie areas established at Becker and at Stillwater, Minnesota, have been monitored over time for legume devopment, plant species diversity and biomass, change in soil properties and for the recovery of inoculant strains and plant dependence on nitrogen fixation. We have driven the Becker prairie toward legume dependence by periodic mowing and removal of residues.This prairie is now well developed with all legumes well established and deriving from 50 to 100% of their N from symbiosis. Changes in accumulation of soil microbial N are becoming evident. Recovery of the inoculant strains from soil is variable but for Dalea is generally high. Rhizobia appear to be concentrated below plants. In this prairie area and in other natural prairie sites we have tested there appears to be significant and unexpected transfer of rhizobia between hosts. In preliminary studies winter wheat has proven to be an excellent alternate host that could perhaps be used to build up numbers of inoculant rhizobia in soil.