Toss a disc, measure your pasture

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by Sonja Heyck-Merlin

In a September webinar titled “Fall Pasture Management,” Susan Truehart Garey discussed a basic method that can be used to monitor and assess pastures in autumn. Garey is an animal science agent with University of Delaware Cooperative Extension. The tool, called the Equine Pasture Evaluation Disc (EPED), was developed by the University of Pennsylvania. While the acronym refers to equine species, the method can be applied to any pasture.

“EPED is intended to give you an objective indication of whether your pastures are in need of some change in management techniques or whether they’re in need of renovation” Garey said.

The EPED is basically a Frisbee with an arrow on it, she explained. “It’s a survey tool intended to help you gather quantitative data related to the composition and density of plants present in your pasture. It is not, however, intended to help estimate or measure forage production.”

While EPEDs are available for sale, graziers can create their own system with a Frisbee. Use a permanent marker to draw an arrow on the outer edge of the disc. The point of the arrow should wrap down around the edge so that it touches the ground. The other necessary tools are an EPED chart, a clipboard and a plant identification guide.

To use the EPED, mentally draw a giant “W” on the pasture. This will be your sample path. Standing at the first point along the “W,” toss the EPED in front of you. It’s okay if the disc does not land flat or lodges on top of plants, but if it lands upside down, throw it again.

If the arrow is touching a plant leaf, stem or seed head, identify the plant and categorize it as either grass, legume or weed, and make a checkmark in the appropriate column. If more than one plant touches the arrow, record only the taller plant. Keep in mind that many grasses will be categorized as weeds depending on your class of livestock. For example, forage to a goat might include browse species which would be weeds to a cow.

If the arrow is touching dead or decaying plant matter, make a checkmark in the plant litter column. If it’s touching organic matter such a lichen, moss or manure, make a checkmark in that column. Make a checkmark in the column labeled “other” if the arrow touches rocks or water. If it’s touching bare soil, make a checkmark in that column.

Pick up the EPED and walk several feet along your “W” path and toss it again. At least 10 data entries should be made for each acre. For pastures greater than one acre, collect data from at least 20 tosses. Garey said, “The more data points you have, the more accurate your assessment will be.”

The next part of your assessment is to calculate the percentage of pasture that is covered by each category. First, add up the number of checkmarks in each column of the EPED chart and place the total at the bottom of each column. To calculate the percentages, divide the number of checkmarks in each column by the total number of checkmarks, then multiply by 100.

For example, if you made 10 tosses and have eight checks in the grass column, then 80% of the pasture is composed of grass forage (8÷10 x 100). If you complete more tosses, then you will need to divide by the total number of tosses. If you have 12 checks in the bare soil column and you made 20 tosses, then 60% of the pasture composition is bare soil (12÷20 x 100).

The final step is to analyze your percentages. First, add together the grasses, legumes and weeds percentages to find your total canopy. “It is considered good if 70% of your pasture is covered with canopy,” Garey said. “If it is below that, your pasture is at risk of sediment and nutrient loss through erosion.” A canopy cover of 80% to 90% is very good, and above 90% is excellent.

It is also important to calculate the percentage of your pasture that is desirable to your animals. An excellent total canopy percentage does not always correlate with high quality forages. To do this, add together the percentages of the grasses and legumes. In well-managed pastures, at least 80% of the total tosses should be these desirable species. Between 70% – 80% is considered adequate. If the concentration of desirable plants is below 70%, it’s time to consider how you can improve the quality of the pasture canopy.

“If your desirable species are from 50% to 70%, you may be able to improve the canopy with no-till seeding,” Garey said. Additional management techniques to consider are lime and fertilizer applications based on soil analysis, pasture clipping and extending rest periods. These practices change the environment to make your desired species more competitive. “If your desired species comprise less than 50% of total tosses, you’re probably looking at a complete renovation,” Garey added.

At a minimum, Garey said the EPED method should be used once a year at the end of the grazing season. She emphasized the importance of storing the data so that graziers can make year-to-year comparisons. “Overall, the EPED strategy is a simple way to quantitatively measure the effectiveness of your pasture management or how successful you may be after implementing a new practice,” Garey said.

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