Home Grazing The Forgey Files -- Contents How Plants Grow

Dave Forgey [Photo by T.L. Gettings]

How Plants Grow
Understanding can help you improve your pasture management.

By Dave Forgey, Logansport, Ind., forgraze@carlnet.org

One of the questions I'm frequently asked by people beginning grazing is, ''How short should I graze my pasture?" Following are some excerpts from a publication called "Hay and Pasture Management" from USDA Natural Resources Conservation Service that help me explain the answer:

"A problem that livestock producers face is knowing how short they can graze or mow the pastures and still obtain maximum productivity during an extended period. The problem is compounded by varying climate conditions, growth habits of different plants and livestock preferences for different plants. Plant growth also is affected by the time of the year and age of the plant when leaves are removed.

"Minerals from the soil make up about 5 percent of the solid material in plant roots, stems and leaves. Carbon, hydrogen and oxygen from the air and water make up most of the other 95 percent.

"The leaves take in carbon dioxide from the air through tiny pores. Using solar energy, the leaves recombine the carbon with oxygen and hydrogen to make sugars and starches. The sugars then combine with minerals from the soils to make fibers, proteins, plant oils and fats. The plants use the sugars, starches, proteins, oils and fats to grow and reproduce.

"The ability of perennial grasses and legumes to recover quickly after grazing and mowing makes these plants extremely valuable for forage production and soil protection. Removing too many leaves retards forage production and damages the plant's root system. Plants eventually die if overharvest of the leaves continues.

"Root growth is closely related to forage production. Plants maintain their maximum root vigor and growth when no more than half their leaves are removed by grazing or mowing during the growing season. If the plant's food producing mechanism is deprived, leaf and root growth are reduced accordingly.

"In all grasses, the volume of leaf removed has a direct effect on the growth of new roots. Roots are the vital supply lines of moisture and minerals to the leaves. Perennial plants store food in the roots after seasonal growth. They use these reserves to live while dormant, to make the first new growth the next spring, and to start new growth after green leaves and stems are closely grazed at any time during the growing season.

"A grass plant produces twice the volume of leaves it need to complete its growth and remain productive. Generally when up to 50 percent of the plant is grazed, root growth continues unimpaired. When 60 to 90 percent of the plant is removed, 50 to 100 percent of the root growth is stopped.

"All plants have growing points where new cells are developed. The growing points of grass are located just above the last complete joints of each stem. Early in the season, the growing points are situated at the base of the plant. As the season progresses, the joints of most species elongate and push upward to produce a seed stalk. At this time, the growing point is elevated and in a vulnerable position. Removal of this point by grazing or mowing forces the plant to send up new leaves from the base plant and to start over as if it were spring. This causes additional drain on root reserves and can weaken the plant."

This is why I tell graziers that you can graze close in the spring but you must leave more leaf surface as the season progresses so that the plant continues to build a strong root system. The better the root system the better the plant can take both heat and moisture stress.

Plants also recover much faster if a large amount of leaf surface remains to start the regrowth cycle. Since the uppermost part of the leaves are the most nutritious for the livestock, it just makes sense to graze the best and leave the rest to speed recovery. I hope this will help explain what is happening out there in your pasture in the summer.

Home Grazing The Forgey Files -- Contents How Plants Grow

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