Essentially, overgrazing is function of both time on the pasture and time away from the pasture. What is known for sure is that overgrazing is detrimental to pasture productivity and, ultimately, livestock performance. Here’s why:
1) Removing too much of the photosynthetic factory (leaves) severely limits the plant’s ability to recover and regrow. Overgrazed plants regrow slowly; if rotations do not allow enough time to reach a grazeable height, these stressed plants are doubly damaged by the next grazing cycle.
2) The plant’s ability to grow new tillers is compromised when plants are routinely grazed too short. Some species keep their carbohydrate reserves in structures below ground, others keep them in the lower one-third of the canopy. Removing these storage structures limits the plant’s capacity to generate new tillers and persist long term.
3) Weeds proliferate when overgrazing occurs. Slowed plant growth and more exposed soil usually result in higher populations of undesirable weed species.
4) Plant root growth is severely impacted. Research studies show that overgrazed pastures result in plants that have shallower root systems with less mass. The lower root volume limits the plant’s ability to take up both water and nutrients, especially during periods of dry weather. Not leaving enough forage residual can cause drought-like conditions even where adequate amounts of rainfall are received.
5) Overgrazing exposes more of the soil surface allowing for a higher degree of runoff, less water infiltration, more soil erosion, and elevated levels of evaporation. Adequate forage cover intercepts raindrops, which slows impact at the soil interface and enhances water infiltration.
6) Animal performance suffers as forage intake declines when pastures are overgrazed. Milk production or gain can be impacted both short and long term if pastures are not given an adequate recovery period after being overgrazed.
~ Mike Rankin, excerpt from Hay and Forage Grower, August 2020. Read the full article here.