One of the benefits of an extended harvest interval with reduced lignin alfalfa is it could extend stand life, spreading out the cost of establishment over another year.
Typically, conventional alfalfa varieties are harvested every 28 days to hit the sweet spot between yield and quality. Reduced lignin alfalfa allows growers to extend that cutting interval by a week, increasing yield without sacrificing forage quality.
The longer life of reduced lignin alfalfa could be coming in two ways, says Kim Cassida, a forage agronomist with Michigan State University.
First, a longer harvest interval allows the alfalfa plant to replenish carbohydrate reserves in the roots more fully. Second, a longer harvest interval means you take one less cutting per season, reducing wheel traffic, compaction and possible crown damage.
Research to date has yet to confirm these benefits, but both make sense intuitively, she says.
“At one-tenth bloom, root carbohydrates are fully restored,” she says, “and that is the basis for waiting for one-tenth bloom. But if you cut at bud stage, you never let carbohydrate replenishment get there.
“And if you repeat this cycle enough times, eventually the plant is out of carbohydrates. This is what causes the decline of stands when we’re on an intensive cutting schedule,” Cassida says.
Taking one less cutting per season also reduces the pressure to cut every 28 days, regardless of weather and field conditions. If you have more time to take the next cutting, you are less likely to go into fields when soils are wet and more prone to damage.
To test the theory of longer stand life, Cassida and her team dug up alfalfa plants in the spring of 2019. The alfalfa was planted in 2015. The researchers saw no difference in stand density among conventional and reduced lignin alfalfa harvested at 28 days, 33 days or 38 days. Cassida was surprised by this, but she notes these were research plots with good fertility and low traffic.
There are also some concerns with extended cutting schedules, she adds. First, growers must be aware of the “stewardship agreements” they sign when they purchase genetically modified, reduced lignin alfalfa varieties.
In the Midwest, the stewardship agreements require growers to cut alfalfa before it reaches 50 percent bloom. In seed producing areas of the West, the stewardship agreement requires reduced lignin alfalfa be cut before one-tenth bloom.
Cassida, who is participating in on-going multi-state trials with reduced lignin alfalfa, says these thresholds were sometimes reached in Michigan. Under dry, stressed conditions, second and third cuttings often exceeded 10 percent bloom at 33 days and sometimes exceeded 50 percent bloom at 38 days. “Other sites did not report exceeding 50 percent stewardship thresholds,” she says.
“[But] early flowering under stress conditions may reduce harvest flexibility for extended harvest intervals,” she notes.
Extended harvest intervals also might run counter to fall harvest recommendations, which say not to cut alfalfa within six weeks of a killing frost. That’s to ensure roots fully restore carbohydrates before frost shuts down the plant’s metabolism. The better option is to simply wait to harvest until after the killing frost. But here again, growers must be aware of the stewardship agreement and stage of flowering for their area.
For a more detailed discussion of Cassida’s findings and recommendations, click here.