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Grazing Consultant: It takes grass to grow grass

forage regrowth and photosynthesis

Over the past few months, several beef producers have asked me the key to having really productive pastures. The simple answer is optimizing plant photosynthesis. Of course, that raises the much more complex question of just how to do it. The first step is to think of your pasture as a solar panel. Consider every acre a 43,560-sq.-ft. solar panel with individual plant leaves as the photovoltaic cells.

The fundamental rule to remember is that only green, growing leaves are effective solar collectors. This means bare ground, dead brown leaves and stems should be avoided, and vegetative green leaves should be maximized. The No. 1 rule in pasture production is it takes grass to grow grass.

Every time you look at your pasture and see bare ground, you should think, "That's a pound of beef I lost." If you think in these terms, you'll start to figure out ways to prevent bare ground from occurring.

Biggest culprit is overgrazing
Grazing pastures too short for too long is the biggest cause of bare ground in tame, high natural rainfall or irrigated pastures. Remember, it takes grass to grow grass. Leaving taller plant residual after grazing will help keep your pastures thicker.

For most cool-season forage species, plan for 3-4-in. of post-grazing residual. Bluegrass and ryegrass with white clover may be grazed somewhat shorter and still maintain vigor. Warm-season species like bermudagrass and bahia can be grazed to 2-3 in. Tall growing native warm-season species like big bluestem and indiangrass should be grazed to 5-8 in., depending on conditions.

Many pasture species require a rest period to be vigorous producers. Rest allows new leaves to develop and regenerate the plant, helping to keep the ground covered. Close growing species like bermudagrass and white clover require the least amount of rest, while tall growing species like bluestem or bromegrass require the most rest.

Maintaining flexibility in your rest management to balance the length of rest period and plant growth rate is fundamental to successful grazing management. The days of rest required for summer-growth pasture may be much longer than that required for spring-growth pasture. Always remember the goal of rest is to allow young green leaves to maximize photosynthesis.

For those using annual pastures, the more you keep your ground covered, the more effective solar collection will be. This means timely planting and minimizing down time on your solar panel.

Overworking the soil is a common problem for many farmers and keeps the ground bare too long. Whether it's a summer or winter annual, try to get the pasture established quickly and maximize sunny growing days for your pasture.

As with any crop, proper fertility and irrigation practices will keep the pasture more dense and vigorously growing. A deficiency of any required soil nutrient can lead to stand thinning and lost photosynthetic efficiency. Soil testing is an important tool for monitoring soil fertility status; then fertilize appropriately.

The three basic inputs for photosynthesis are solar energy, carbon dioxide and water. If pastures are short on water, photosynthesis declines rapidly. Managing soil conditions for a healthy water cycle, and timely irrigation, are keys to keeping water availability appropriate.

Avoid over resting pastures
I've already mentioned the importance of rest for some pasture species. Avoiding over rest, however, is just as important to photosynthetic efficiency as avoiding over grazing. Over-rested pastures have a preponderance of aged, dead leaves that provide no photosynthetic output for the plant.

An individual blade of grass only has an effective photosynthetic life of three to four weeks. After that, it's losing its photosynthetic efficiency, as well as losing nutritive value for the cattle.

Maximizing photosynthesis is the key to having truly productive pastures. A primary goal of grazing management is keeping forage growth vegetative and density of ground cover high to maximize solar collection. Always remember, it takes grass to grow grass.

Jim Gerrish is a grazing management consultant based in May, ID, and former lead pasture researcher at the University of Missouri's ForageSystemsResearchCenter in Linneus. Reach him at 208/876-4067, or visit