Fall harvesting alfalfa
August 15, 2008
If you've never fall-harvested alfalfa before, this may be the year to give it a try. High-quality forage supplies are short due to various weather challenges, so the economic value of high-quality forage remains high, especially in light of high grain and fuel costs. Late summer into fall usually provides favorable growing conditions for alfalfa growth, so harvesting that growth should be considered. Let's review a few factors to consider with fall harvesting.
- Timing of the fall cut. Research data continue to mount supporting the concept that timing of the fall cut matters little as long as other factors (e.g. variety, fertility, drainage) favor fall-cutting tolerance. Farmer experience must agree, as I have noted more September cutting in my travels over the last several years. However, for the risk-averse, either avoiding fall cutting or waiting until mid-October may be better options. Waiting until mid-October minimizes the chances of significant regrowth and root reserve depletion after cutting. But don't be concerned about waiting for an alfalfa-herbage-killing frost (around 20º F) before harvesting. That approach risks significant leaf loss and unfavorable curing conditions.
- Previous cutting frequency. Stands cut more frequently are at greater risk of winter injury if cut during the fall. Thus, when other factors favor fall-cutting tolerance, a third harvest during fall is rarely risky, a fourth harvest during fall can be somewhat risky, and a fifth harvesting during fall can carry considerable risk. Key to enhancing winter survival is allowing at least one crop during the growing season to mature to mid-bloom. Thus, stands of fall forage that have previously been cut at pre-bloom stages should be well-flowered if fall harvest is considered.
- Recent North Dakota data. Working with two varieties in replicated plots at Fargo, Dr. Dwain Meyer showed a 3-year total yield gain of 3.6 ton per acre by taking a fourth harvest in fall for three consecutive years compared to just three harvests per year. A key aspect of his 4-cut system was that the fourth harvest was taken when alfalfa plants attained either 40 to 50% bloom or 2 to 3 inches of new shoot growth from the crown; corresponding to Oct. 7, Sept. 28, and Sept. 13 in 2004, 2005, and 2006, respectively. There was little to no evidence of winter injury each spring through 2007.
- Quality and yield next spring. We've conducted fall-cutting experiments on two farms in southeastern Minnesota. On one farm, fall residue after a third cutting in mid-August significantly reduced quality of the next year's first cutting. On the second farm, it did not. Some Wisconsin data indicate little affect of fall residue on spring quality. Thus, fall residue more often than not has little detrimental affect on quality the next spring. But if there is a lot of fall residue and it doesn't get matted down by snow over winter, it may reduce quality next spring. If that is a concern next spring, fall residue can be clipped when the ground is still frozen before spring regrowth starts; however, this can be a challenge to time without damaging the stand. Fall cutting can delay growth next spring. While this can be alarming initially, especially when neighboring non-fall-cut fields of alfalfa are jumping, any yield delay/loss is usually far less than the yield harvested/gained the previous fall.
- Grazing. Grazing is a great option for "harvesting" alfalfa in the fall. Patterns of use by grazing animals often leave stemmy stubble for catching insulating snow. But don't graze when the soil is wet, lest stand damage occur. Alfalfa-grass mixtures can be grazed during somewhat wetter fall conditions. Follow bloat precautions if grazing pure alfalfa, especially right after a killing frost.
- Uncut strips and/or higher residual height. While there are no research data substantiating the benefit of uncut strips perpendicular to prevailing winter winds and <20' apart, or leaving a taller (>6") stubble to help catch insulating snow cover, anecdotal evidence suggests these practices may reduce fall harvest risk.
- Shorter rotations. Even the best varieties with the best management begin to lose yield potential in their third year. Thus, on many farms where nitrogen (N) credits from alfalfa can be effectively used by a subsequent corn/grass crop, keeping stands beyond 3 to 4 years may not be economical. Remember that stands need >55 stems per ft2 to have greatest yield potential. Stands in the 30 to 40 stems per ft2 range may not appear to be weak from the road, but lack the yield potential of denser, healthier stands. In addition, alfalfa production costs are too high to limp along with marginal yields. If you lose a stand due to fall cutting, capitalize on the latest alfalfa genetics in another field next spring, and consider mixing with a high-yielding, hardy grass for insurance.
For more information on forages, visit the University of Minnesota Forage web site at www.extension.umn.edu/forages/.