Forage grass allelopathy in birdsfoot trefoil establishment

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Nathan Blake and James B Kotcon, Davis College of Plant and Soil Science, West Virginia University, Morgantown, WV

Background/Question/Methods
The major limiting factor in small ruminant production is gastrointestinal nematode (GIN) infection. Severe cases can result in low weight gain, decreased milk production, and even death. Currently, all financially viable GIN treatments involve synthetic medications that void organic status of treated animals. Some tanniniferous forages such as birdsfoot trefoil (BFT) have been shown to suppress GIN infection and provide dietary benefits when grazed in pasture. BFT can reseed itself, but it has proven difficult to establish in pasture. This project assessed inhibitory interactions between common forage grasses and BFT. Eight forage grasses (kentucky bluegrass, meadow fescue, orchardgrass, perennial ryegrass, reed canarygrass, smooth brome, tall fescue, and timothy) were cultivated in a greenhouse. Harvested, mature residues were used to prepare a serial dilution of extracts. Extracts were used to assess allelopathic inhibition of BFT germination and radicle emergence. Root leachate was captured and used in a similar serial dilution bioassay.
Results/Conclusions
Statistical analysis showed that extracts prepared from leaf residue significantly inhibit BFT germination and radicle length (p<0.0001). Extract concentration was also significant (p<0.0001). No Observable Effect Level was used to assess toxicity. Toxicity varied greatly by grass. Smooth brome and perennial ryegrass were the least toxic, reaching a NOEL at the highest concentrations when compared to other grasses. Reed canarygrass and tall fescue were the most toxic, reaching a NOEL at the most dilute concentrations when compared to other grasses. Root leachates from the grasses did not significantly inhibit BFT germination or radicle elongation.

Data from this experiment show that grasses present in existing pasture allelopathically inhibit BFT establishment. The composition of a pasture greatly affects chances of BFT establishment. Concentrations of extracts were such that some concentrations were representative of residue amount that would be present in an existing pasture after a grazing event or mowing. The amount of allelopathic inhibition of the most inhibitory grasses present at the pasture-comparison levels inhibited germination by as much as 54%, indicating that knowledge of pasture composition and seeding into less inhibitory grasses will be crucial to successfully establishing BFT in existing pasture and preventing GIN infection through the use of tanniniferous forages.