May 13, 2021

Increasing pasture productivity: Leaves are the solar panels for forage crops

CENTENNIAL, Colo. — Cattlemen that develop a rotational grazing system are managing the carbohydrate status and the leaf area of the forage.

“When we manage those two things we can increase the pasture productivity about 30%,” said Chris Teutsch, Extension associate professor and forage specialist at the University of Kentucky.

“Photosynthesis is the most important biochemical process on earth,” said Teutsch during the Cattlemen’s Webinar Series organized by the National Cattlemen’s Beef Association. “It is the process by which light energy from the sun is converted into chemical energy by the plant.”

Two types of grasses — bunch grass or sod formers — are grown in pastures.

“Bunch grasses like tall fescue or orchard grass grow in a clump and sod formers like Bermuda grass form rhizomes and stolons that allow the plants to spread out and form a dense sod,” Teutsch said.

Bunch grasses are less tolerant to close grazing.

“They have a fibrous root system with about 90% of their roots in the upper 10 inches of the soil,” Teutsch said.

“Rhizomes grow just under the soil surface and stolons grow just above the soil surface and both store carbohydrates and allow the plant to spread out so they can fill the sod in,” he said.

The leaf area on a plant is like a solar panel.

“The more leaf area we leave, the faster the pasture will regrow,” Teutsch said. “If we graze the pasture tightly, we’re removing the ability of the plant to capture sunlight.”

The second place the plant gets energy to regrow is from stored carbohydrates in the plant and plants store carbohydrates in different places.

“Cool-season, bunch-type grasses store carbohydrates in the stem base,” Teutsch said. “If they are grazed real close, that removes its ability to capture sunlight and by getting down to the stem base where it is storing its energy that’s a double whammy on the plant.”

Bermuda grass stores its carbohydrates in the stolons and rhizomes.

“The carbohydrates are safely below the grazing height by the animal, so even if they graze the pasture tightly, they are not taking away the carbohydrate reserves,” Teutsch said.

“Alfalfa is 100% dependent on stored carbohydrates in the tap root of the plant,” he said. “When the alfalfa plant starts to regrow, the carbohydrates stored in the roots decline rapidly until the plant reaches 6 to 8 inches tall and has regained its leaf area.”

At this point, the plant is capturing enough sunlight to convert it into sugars and carbohydrates.

“It is able to fuel its regrowth plus the extra gets shifted into storage in the plant,” Teutsch said.

Cattlemen need a good attitude when starting a rotational stocking system, he said.

“If you think this is never going to work, the chances you’ll be successful are pretty thin,” he said.

Water is key with controlled grazing systems.

“It is critical to think about how to lay out the water source,” Teutsch said.

“There will be improved nutrient cycling and improved distribution of dung and urine with a rotational system,” he said. “The smaller you make the pastures, the better the distribution pattern.”

Cattlemen should develop their rotational stocking system based on their wants and needs.

“If you want to move your animals once a week, you set up your system to do that,” Teutsch said. “That will be much better than letting the animals continuously graze.”

It is important to build some flexibility into the grazing system, Teutsch said.

Fenced In

“Power fencing is a psychological barrier and you only need three things — an energizer, posts and wire,” said Jeremy McGill, territory manager and regional product specialist for Gallagher Animal Management, North America.

“Problems occur when there is not enough power, not a big enough energizer or the wrong type of wire is used,” McGill said.

“The ground system is the most overlooked part and where most failures occur,” he said.

“You need three ground rods, 10 feet apart, 6 feet deep and a continuous wire that connects them all together,” he said. “You don’t want to mix metals and never join copper and galvanized together because that makes it harder to conduct energy.”

To select the correct power level, McGill said, cattlemen should choose the energizer that will pull the greatest load that the operation will require.

“Select a larger energizer than what you think you need,” he said. “The amount of power you need depends on the distance of the fence, the type of animal you’re controlling and the amount of interference on the system.”

Wire selection should be based on conductivity, visibility and portability.

“The gold standard for conductivity is hi-tensile wire, 12.5 gauge, galvanized steel,” McGill said. “However, it’s not very portable, so it is designed more for permanent fencing.”

Polywire is more portable and it can be used for fencing 1,000 feet or less, McGill said.

“For visibility, cattle and wildlife can contrast white the best,” he said. “If wildlife can see the fence, they will also respect it.”

Martha Blum

Field Editor