In another experiment, Crider
showed the effect that a single removal of top growth, in 10 percent increments, has on root growth. When 40 percent or less of the for-
age is removed, 0 percent of the roots stop growing. When 50 percent or more of the for-
age is removed, an increasing percent- age of the roots stop growing. When 90 percent of the forage is
removed, 100 percent of the roots stop growing (Table 1). In other words, leaving more than
half of the forage any time a plant is grazed during the growing season al- lows the roots to continue to grow. If the roots keep growing, so should the forage. Not only did the higher percentages
of forage removed result in greater per- centages of roots that stopped growing, the higher percentages also resulted in greater lengths of time before the roots resumed growth. Thirty-three days after top growth removal, plants with 80 and 90 percent of their forage removed still had a portion of their roots that had not resumed growth. In a companion experiment, Crider showed how re- peated removal of forage affects root growth. Like the
Table 1: Percent Root Growth Stoppage 3 Days After Forage Removal
Percent
Forage Removal 90
80 70 60 50 40 30 20 10 0 Test 1 100 100 78 50 2 0 0 0 0 0 Test 2 100 100 97 80 8 0 0 0 0 0 Test 3 100 91 77 54 38 0 0 0 0 0 Test 4 100 81 76 36 13 0 0 0 0 0
This represents 4 tests with 3 grass species. From Crider, 1955. Note that somewhere between 40 percent and 50 percent of the forage can be removed without stopping root growth.
tscra.org Editor’s note: Jim Johnson serves as a soils and crops
consultant in The Samuel Roberts Noble Foundation agricultural division’s consultation program.
February 2015 The Cattleman 73
previous experiment, removal of a percentage of top growth, in 10 percent increments, was done. However, in this experiment, forage was repeatedly removed to the height of the initial removal 3 times per week for 5 weeks. This time, 33 days after initial top growth removal,
plants with 50 percent or more of their forage removed still had a portion of their roots that had not resumed growth, and none of the roots had resumed growth on the plants with 70 percent or more of their forage removed. So removing half or more of the forage at a time
stops root growth whether cattle graze rotationally or continuously. However, leaving half or more of the forage allows root growth to continue uninterrupted. If the roots grow more, the forage grows more; in the long run, more forage will come from the half that is grazed. The entire article by Crider can be found by look-
ing up Root-Growth Stoppage Resulting From Defolia- tion of Grass by Franklin J. Crider, Technical Bulletin No. 1102, United States Department of Agriculture, February 1955.
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