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SOIL HEALTH IN PRACTICE - REAL SOLUTIONS FROM REAL FARMERS

The Effect of Grazing on Plant Root Growth forage is removed, zero percent of the roots stop grow-
ing. When fifty percent or more of the forage is removed
Over the years, I have seen many grazing operations in many from perennial grass, an increasing percentage of the
parts of the country. I have seen places that never seem to roots stop growing. When ninety percent of the forage is
grow as much grass as they should, and I have seen places removed, one-hundred percent of the roots stop growing.
that always seem to have lots of grass. Likewise, I have seen In other words, leaving more than half of the forage any
places that have been hurt by the extreme weather of the time a perennial grass plant is grazed during the growing
past several years, and I have seen places that have tolerated season allows the roots to continue to grow. If the roots
the extreme weather quite well. The places that have lots of keep growing, so should the forage. Not only did higher
grass and are doing well don’t necessarily have better soil or percentages of forage removed result in greater percent-
get more precipitation, and they may not be stocked light- ages of roots that stopped growing, the higher percentages
er or rested more days per year. So what is the difference? of forage removed also resulted in greater lengths of time
Roots and the effects that management has on the roots. before the roots resumed growth. Thirty-three days after

top growth removal, plants with eighty and ninety percent
of their forage removed still had a portion of their roots
that had not resumed growth.

So, whether cattle are grazed rotationally or continuously
on perennial grasses, removing half or more of the forage
I have always known that grazing management affects roots, at a time stops root growth. However, leaving half or more
but it was made crystal clear to me when I was introduced of the forage allows root growth to continue uninterrupted.
to work that F.J. Crider published in 1955. Through sever- If the roots grow more, the forage grows more, and in the
al experiments, using various perennial grasses, he showed long run, more forage will come from the half that is grazed.
the effects that forage removal has on root growth. He The entire article by Crider can be found by looking up
used both cool and warm season grasses including smooth Root-Growth Stoppage Resulting From Defoliation of
brome, tall fescue, switchgrass, bermudagrass, and several
others. In one experiment, Crider showed that when more Grass by Franklin J. Crider, Technical Bulletin No. 1102,
United States Department of Agriculture, February 1955 or
than half of the forage is removed from a plant, root growth
stops within the first day or two afterward, and stays stopped by going to www.greencoverseed.com.
from six to eighteen days, with an average of eleven days. In
the real world, this means if cattle have the opportunity to By Jim Johnson • Ardmore, OK
graze more than half of the top growth of a perennial forage Noble Research Institute
grass, at an interval less than eleven days, the roots never Johnson serves as a soils and crops consultant in
the producer relations program, where he assists
get to recover. If the roots don’t recover, eventually, neither regional agricultural producers with soil fertility
will the top. testing, recommendations and management; pesti-
cide recommendations; integrated pest management; sprayer and planter
In another experiment, Crider showed the effect that a calibration; variety selection; and agronomic best management practices.
single removal of top growth, in ten percent increments, Johnson has more than 20 years of experience in plant and soil sciences.
has on root growth. When forty percent or less of the Johnson, his wife, and children, also run a small cow-calf operation in
south-central Oklahoma.

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