Close only counts with horseshoes and hand grenades, according to the old adage. But close cutting also counts for hay growers who want to maximize yields, says a North Dakota State University agronomist.
"I recommend that they cut their alfalfa as low as they possibly can - ideally to a 1" stubble height, or at least as close to it as rocks, gopher mounds, equipment and field conditions allow," says Dwain Meyer.
Meyer has been studying the effects of cutting height on alfalfa yield for several years. Most of his trials have compared Vernal alfalfa under two- and three-cut systems. But his latest trial compared that variety under three- and four-cut systems.
The newest data, averaged over two years, show that a field cut to a 1" stubble height yielded 6.05 tons of dry matter per acre in the three-cut system. Alfalfa yielded 5.17 tons when cut to a 3" stubble height in that system; 4.5 tons with 5" stubble.
Under the four-cut system, fields cut to 1, 3 and 5" stubble heights yielded 6.38, 5.37 and 4.67 tons/acre, respectively.
"The increase in yield that can be achieved by lowering the cutting height just amazes me," says the agronomist.
Most of that gain isn't simply from harvesting more of the plants at each cutting, Meyer says. It's from increased growth from stems originating from the crown rather than from axillary buds on the lower portions of the stems.
The biggest yield differences among the three stubble heights occurred during the first cutting. Under both the three- and four-cut systems, the field cut to a 1" stubble height yielded about 0.8 ton more per acre in the first cutting than the field cut to 5".
"The surprising thing to me is the amount of yield we lose in the first harvest with the taller stubble heights," says Meyer. "We don't actually know why. Lodging is the most logical explanation, but I just don't believe that's what it is."
The researchers hand-harvested alfalfa this year to see if stem size could explain the first-cutting yield differences. The lower stem (last 4") only accounted for about half the difference, or about 0.4 ton/acre.
Meyer says stubble height has a bigger impact on alfalfa yield than on forage quality. The newest data show that alfalfa cut to 5" stubble heights tested one to two percentage points higher in crude protein and three to five points higher in dry matter digestibility than alfalfa from fields with 1" stubble. But the yield advantage from cutting shorter easily offsets the enhanced quality, he says.
He's currently evaluating new, faster-recovering varieties to see if they respond differently.
"Thus far, the faster-recovering varieties have a greater percentage of stems originating from remaining stubble than Vernal. It will be interesting to see if these varieties respond differently to stubble height."