Sometimes new machinery technologies solve one problem but create a new one. That might be the case when it comes to disc mowers, which have largely replaced sickle bar mowers on most haymaking operations.
“One of the issues that has developed with disc mowers is the tendency for producers to cut their fields very short,” says Gary Bates, director of the University of Tennessee Beef and Forage Center (UT-BFC). “It isn’t unusual to see a 1- or 2-inch stubble height after a producer has cut hay with one of these (disc-type) mowers,” he adds.
Bates points to numerous research studies that show stubble height has a direct influence on the persistence of cool-season grasses such as tall fescue or orchardgrass.
“The recommendation from these studies is to leave at least three inches of stubble,” Bates notes in a recent UT-BFC blog post. “Cutting below that height will reduce the persistence of the stand, shortening its productive life.”
Many cool-season grasses store carbohydrates in the lower 2 inches of the stem. If cut below this height, especially on a consistent basis, regrowth is impaired.
In addition to removing carbohydrate reserves, a low-cutting height also removes more photosynthetic leaf area. This further impedes the plant’s ability to regrow quickly. Over time, stand persistence and productivity will suffer.
“I have been asked several times why tall fescue and orchardgrass fields don’t presently last as long as they did in the past,” Bates comments. “Part of that could be simply due to our memories. Things often seemed better in the past compared to current conditions. But a lot of it is due to how close a field is cut during hay harvest,” he adds.
Bates says that one of the best checks a producer can make is that of residual cutting height. He suggests no less than a 3-inch stubble for grasses such as tall fescue and orchardgrass. For taller grasses like sorghum-sudangrass and native warm-season species, leave 6 to 8 inches of residual.
There really are few downsides to a higher grass cutting height. More low-quality stem is left in the field, regrowth is hastened, stand health and long-term productivity are preserved, and the risk for forage soil contamination is reduced.