Many livestock producers are using high-intensity livestock grazing to improve soils and plants in pasture. Andrea Clemensen has investigated how grazing and fertilization affects soil organic matter, nutrients, and microorganisms. Along with that, she also looked at amounts of nutrients and secondary compounds in alfalfa, birdsfoot trefoil, reed canarygrass, and endophyte-infected tall fescue.
Alfalfa contains saponins and birdsfoot trefoil contains tannins. Both plants fix nitrogen
improving pasture growth and the crude protein content of forage. Endophyte-infected tall fescue produces two types of alkaloids, those associated with the plant and those from a fungus that lives in the grass. Reed canarygrass contains eight alkaloids.These secondary compounds benefit the plant by reducing the need for pesticides and herbicides.
From 2009 to 2011, Andrea also examined how cattle grazing at high stock densities or hay production (no grazing) affects soils and plants growing in mixtures or monocultures. Trefoil samples were analyzed for condensed tannins, fescue samples anaylyzed for the alkaloid ergovaline, reed canarygrass samples for the alkaloid gramine, and alfalfa for saponins.
Finally, Andrea investigated how plants respond to nutrient inputs from animal impact by
applying commercial fertilizer, green manure and fecal manure to each of these forage species growing in monoculture.
Concentrations of secondary compounds varied during the growing season. Saponins in alfalfa ranged between 0.8% and 5%. Tannins in birdsfoot trefoil ranged between 0.8% and 8%. Saponins and tannins were lowest in May and highest in July. Alkaloids (ergovaline) in tall fescue ranged between 60 to 350 ppb with the lowest concentrations in May and the highest in August.
Concentrations of saponins or tannins in the legumes did not change when grown next to tall fescue. However, tall fescue growing near legumes had much higher concentrations of
ergovaline and crude protein than tall fescue growing in a monoculture.