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The Grazier's Gazette

Weeds are tattletales

cattle in pasture with weeds
Pasture weeds are broadcasting the fact we didn't control livestock and give forage plants time to recover after grazing.

My mailbox has been full of advertisements for pasture weed poisons lately, so evidently it is time for my periodic rant about why we have pastures with more weeds than grass.

Weeds do not invade; they just grow where our management makes it difficult for the plants we favor to do well.

Probably number one on the list of weed causing management faults is starving our forage plants by reducing the amount of sunlight they can convert to biological energy (sugar). This is quite easy. Just reduce the amount of green leaf area and keep it low by having grazing animals constantly present to pluck each new leaf before it has enough quality growing time to produce at least as much energy as the plant required to grow the leaf. This will undo several things:

  • It will dramatically reduce the amount of forage produced, both standing crop and over time.
  • It will reduce soil life by halting the transfer of root exudates (mostly sugars and starches) from plants to the soil microbes that are responsible for making mineral nutrients available to forage plants.
  • The loss of soil life will also reduce the ability of the soil to take in and store water.
  • It will increase the amount of bare ground, greatly decreasing the quality of local growing conditions.
  • It will promote loss of soil to water and wind erosion.

In short, it will set up the conditions that favor the growth of weeds over the growth of forage plants. The weeds that come into the pasture sward do so because they are better adapted to the degraded environment created by abusive grazing then are the plants we favor. Nature will always try to cover the ground with plant material to reduce the waste of sunlight, water, and soil.

Whether the ground cover is forage plants or weeds depends on how an area is managed.

Killing the weeds without changing the conditions that gave them the advantage will only make the long-term situation worse.

It is sometimes hard for people, including some range scientists, to understand how damaging continuous grazing is to all parts of the soil-plant-microbe-animal complex.

In part, that may be because it is not uncommon to see, in mid growing season, continuously grazed pastures stocked at conservative rates that have a lot of vegetation present. The pastures don't look too bad, but looks can be deceiving.

Much of this forage will contribute little to the health and productivity of the forage sward because it is overly mature. Individual plants not grazed early in the season will, by mid season, contain a lot of stems and senescent leaf material that is inefficient in photosynthesis and shades sunlight from younger plant material.

Forage plants require periodic defoliation to maintain health. The older material slows growth of the entire sward. Neither is it quality forage for grazing animals, as both digestibility and protein content are low.

Most of the rest of the forage present will have been grazed early in the season and then re-grazed every time it got large enough to be bitten. This material is high-quality forage to the grazing animal but will produce little because it has been weakened by repeated defoliation. Continued long enough, the over grazed plant will die.

This explains why there may be a lot of forage present in the continuously grazed pasture, provided stocking rates are low, but there is little plant life that is truly healthy except for unpalatable weeds.

Anything that damages the ecological processes will cause weed and brush encroachment, but by far the most important is a lack of quality growing time between defoliations.

Livestock producers all over the world have learned this and manage to control weeds by providing forage the quality recovery time needed. This works not by killing weeds but by changing growing conditions so that the weeds no longer have an advantage over the forage plants.

Weeds cannot stand prosperity; improve the water cycle, the nutrient cycles, and energy flow and weeds become a non-problem.

It takes time but once the soil and forage health is restored, very few inputs are required to maintain production at high levels.

There are costs associated with controlling where and how long animals graze, but the benefits of holistically planned grazing far outweigh the costs. Weed control is only one of the benefits that can be achieved through planned grazing. We will explore more of these in the future.

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