Posted: Thursday, August 11, 2011 12:00 PM
By DOUG WARNOCK
For the Capital Press
A high level of diversity in the plant community makes for a more sustainable food source for the grazing animals, says Fred Provenza, an animal scientist at Utah State University.
Provenza specializes in researching the grazing behavior of livestock and learning about managing animal behavior. He promotes managing for sustainability and is a champion for plant diversity.
With the onset of hotter weather we are seeing the benefit of having legumes in the pasture mix. Graziers with irrigated pasture and those living in areas with higher precipitation are able to include alfalfa, clover or other legumes in their pasture.
The legumes tend to increase growth activity in warmer weather, which makes up for the decline in growth that occurs with the cool season grasses that are prevalent in the Northwest. This is one illustration of the benefits of plant diversity.
Diversity in the types and varieties of grasses can help to lengthen the grazing season and reduce the amount of hay or silage fed during the winter. Some grasses start earlier in the spring and others grow longer into the fall. With some of both kinds, we can have a longer grazing season.
Legumes grow symbiotically with rhizobia bacteria that form nodules on the plants' roots. These bacteria use plant carbohydrates to reduce, or "fix," nitrogen from the atmosphere. Thus, they provide a natural source of nitrogen in the soil and reduce the need for nitrogen fertilization.
Another advantage of diversity is the difference in nutrients provided by different types of plants. Legumes generally provide more protein than grasses and are better sources of calcium than grasses.
Grasses, on the other hand, are better sources of phosphorous. So, by having both in the pasture, the grazing animals have a more balanced diet.
Provenza reports that all plants contain secondary or toxic compounds, which tends to limit the animals' intake of any one plant. Given enough of a variety of plants on which to graze, animals will regulate their intake of any single plant. Consequently, they tend to balance their diet for nutrients and limit their intake of toxins.
Grazing on a variety of plants is the best way to do this, because different secondary compounds are processed at different rates through varying metabolic pathways and this provides several avenues for detoxification. Animals have a built-in mechanism to ensure that they eat a variety of plants and graze in different areas, if allowed.
Having choices on pastures and rangelands allows livestock to meet their needs for nutrients and regulate their intake of secondary compounds. A diverse plant community offers animals a more sustainable landscape in which to graze.
Conversely, a monoculture or less diverse plant community tends to lead to more nutrient deficiencies and greater chances of toxicity problems, due to the limited choices available.
Doug Warnock, a former Washington State University Extension agent, lives on a ranch in the Touchet River Valley.