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Don’t buzz-cut your hay acres

Researchers find the optimum cutting height for cool- and warm-season grasses to improve the stand.

May 19, 2023

2 Min Read
pasture mowing with blue tractor and mower
HAY HARVEST: Mowing hay at the correct height can ensure multiple cuttings throughout the growing season. Tofotografie/Getty Images

Avoid the temptation to scalp your stand of grass, MU Extension agronomist Tim Schnakenberg says, as pastures cut too short may require future renovation or replanting.

He and other university researchers agree — the optimum cutting height for cool-season grass is 4 inches, and 8-inch cuttings for native grasses. Still, farmers like to get as much forage as possible.

Doing these things creates problems:

Cutting forage too low. This reduces the amount of leaf exposed to the sun. Plants need some leaf residual to capture energy from the sun to rebound from cutting. Without enough leaves, the plant must rely on root reserves to bounce back for the next cut.

Cutting too much top growth. Doing this in grasses removes growing points and reduces the amount of leaf exposed to the sun. If leaves are cut too short and too often, roots die back because there is not enough photosynthesis to feed them.

Removing all top growth. This can sometimes set grass back two weeks, which reduces the growing season by two weeks for the year each time it is scalped.

Cutting too many leaf swards. This consistently weakens the plant and makes it less resilient over time. Good root systems help plants withstand dry periods.

Ultimately, Schnakenberg says, cutting height greatly affects persistence.

Higher cuts improve stand

Research on orchardgrass from Ray Smith at the University of Kentucky compared the effects of half-inch, 2-inch and 4-inch cutting heights.

Here’s a breakdown of cutting height and the percent of stand left after the fifth cutting:

Half-inch. 16% to 22%.

2-inch. 45% to 50%

4-inch. 96% to 100%

High cuts lead to more weeds, but lower cuttings also lead to more weeds.

The research also showed significant differences in weed infestations. The percentage of weed in the half-inch cutting was 48%, 12% on the 2-inch cutting, and only 5% on the 4-inch cutting.

“This is a great reminder that low harvests open up the forage canopy and allow light to penetrate. Bare soil gets exposed, allowing weed explosions in the field,” Schnakenberg says.

“Sunlight exposure to bare soil also heats up the soil in the summer months and weakens both the crowns and the root systems of cool-season forages already suffering in the heat. A residual cover acts as an insulator in many ways for the crop against the harshness of the environment.”

High cuts mean more tonnage

Schnakenberg cites older studies from the University of Tennessee that show that higher cutting of 10 inches in sorghum-sudangrass yielded the highest tonnage and best quality throughout the season compared to the 1-inch and 6-inch cuttings in the same study.

Contact your local MU Extension agronomist to learn more about harvest cutting heights for your forages.

Source: University of Missouri Extension

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