Page Banner

United States Department of Agriculture

Agricultural Research Service

Title: Effect of cowpea and pea inocula on cool-season grasses.

Authors
item Williams, Robert
item Bartholomew, Paul

Submitted to: Allelopathy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 4, 2006
Publication Date: April 15, 2008
Citation: Williams, R.D., Bartholomew, P.W. 2008. Effect of cowpea and pea inocula on cool-season grasses. Allelopathy Journal. 21(2):381-388.

Interpretive Summary: Before planting, legume seeds are generally inoculated with either Rhizobium or Bradyrhizobium bacteria that form nitrogen fixing nodules on the plant roots. These bacteria also produce plant growth hormones which can stimulate plant growth, or other compounds which may inhibit pathogenic bacteria. In some cases non-legume crops, such as corn and rice inoculated with these bacteria have shown greater plant growth as compared to un-inoculated plants. Here we used commercial inoculum and non-sterile soil to evaluate the possible effects on typical cool-season forage grasses: Italian ryegrass, tall wheatgrass and tall fescue. Our hypothesis at the beginning of the study was that the legume inoculum would not have an effect on the cool-season grass growth, or at best, based on the general trends in the literature, the inoculum might have a slight positive effect on grass growth. Seeds of each grass were inoculated with either cool- or warm-season forage legume inoculum, and the seedlings were grown under controlled environmental conditions and harvested at either 4 or 6 weeks after emergence. Plant dry weight was reduced by both inoculum treatments, but the effect was greater with cool- than with warm-season inoculum. Although only early seedling growth was evaluated, it is expected that the inhibition of seedling growth would reduce the competitiveness of the grasses and result in reduced yields.

Technical Abstract: Rhizobium or Bradyrhizobium bacteria, which form nitrogen fixing nodules on the legume plant roots, also produce plant growth, or other compounds that may inhibit pathogenic bacteria. Non-legume crops, such as corn and rice, inoculated with these bacteria have shown greater plant growth as compared to un-inoculated plants. This increase in plant growth was attributed to eggects of plant growth regulators released by the rhizobial bacteria. Inoculated forage legumes are often planted with forage grasses. The possible effects of rhizobacteria inoculum on forages grasses have not been evaluated. Here commercial inocula and non-sterile soil to simulate field conditions were used to evaluate the possible effects of Rhizobium and Bradyrhizobium on the early growth of three cool-season forage grasses: Italian ryegrass (Lolium multiflorum Lam.), tall fescue (Festuca arundinacea Schreb.) and tall wheatgrass [Elytrigia elongata (Host) Nevski]. The grasses were inoculated with cowpea (Bradyrhizobium sp., a warm-season legume inoculum) or pea (Rhizobium sp., a cool-season legume inoculum) inocula. The grass seedlings were grown under controlled environmental conditions and harvested at either 4 or 6 weeks after emergence. Plant dry weight was reduced by both inoculum treatments, but the effect was greater with cool- than with warm-season inoculum. Overall the pea inoculum reduced root and shoot dry weight by 29% and 20%, respectively, while the cowpea inoculum reduced root and shoot dry weight by 11% and 2%, respectively. Although only early seedling growth was evaluated, such a delay or inhibition of seedling growth would reduce the competitiveness of the grasses and result in reduced yields.

Last Modified: 10/22/2014
Footer Content Back to Top of Page