For the best combination of yield and quality, cut alfalfa as short as possible, advises Daniel Wiersma.
"From a yield standpoint, we’re seeing very significant differences, and quality changes aren't that great," says Wiersma, an agronomist at the University of Wisconsin's Marshfield Ag Research Station.
In his tests the past two seasons, total dry matter yield from three cuttings increased an average 1/2 ton/acre for each 1" reduction in cutting height. Lower cutting reduced relative feed value by about four points per inch. But potential milk yield per acre – a combined measure of forage yield and quality – increased by 900 lbs/acre for each 1" reduction in cutting height.
Wiersma’s findings are similar to those reported earlier by agronomist Dwain Meyer at North Dakota State University. He found significant yield gains from cutting alfalfa as low as 1".
Meyer says most of the yield gain from close cutting isn't simply due to the fact that more of the plants are harvested each time. It’s due to increased growth from stems originating from the crowns rather than from axillary buds on the lower portions of stems.
Wiersma is beginning the final year of the three-year study. Two tests were conducted at Marshfield in 1999, and a trial was added at another central Wisconsin location last year. In each case, cutting-height treatments ranged from 2" to 6".
Average season-long yields both years were 5 tons/acre for the shortest cutting height; 2.5 tons/acre for the longest.
He recommends that growers leave a 2" stubble when cutting healthy, unstressed alfalfa in spring and summer. Adjust cutting height upward when the crop has been stressed by drought or flooding, or in fields that have been cut early and often. If a fall cutting is taken, leave a 4" stubble to catch snow.
Close cutting takes planning, Wiersma adds. "You have to work hard to get rid of rocks," he says. "We seed with a grain drill and press them down with a cultipacker-type roller behind the drill."