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Managing and feeding reduced-lignin alfalfa

Everett D. Thomas for Progressive Forage Published on 02 October 2019
Cutting alfalfa

There’s a lot of interest in reduced-lignin alfalfa, with these alfalfa varieties now available from at least half-a-dozen seed companies. All HarvXtra varieties of reduced-lignin alfalfa are genetically engineered, glyphosate-tolerant (Roundup Ready) and have a fall dormancy of 4.

The fall dormancy rating shouldn’t restrict their use in most regions of the northern U.S. since relatively few alfalfa varieties currently on the market have fall dormancies of 2 or 3. Winter survival ratings are probably more important than fall dormancy is, and all HarvXtra varieties (as well as Hi-Gest 360, also promoted as having reduced lignin) are rated 1 or 2 for winter survival, with 1 the top rating.

Reduced-lignin alfalfa offers farmers much more flexibility in their harvest schedules. At the bud stage, HarvXtra varieties have very high digestibility and, as the plant matures, digestibility decreases (as it does in all perennial forages) but quality is very good at least until it reaches the early bloom stage. HarvXtra alfalfa also tends to be slightly later in maturity than conventional alfalfa varieties. The result is a much wider harvest window for farmers growing HarvXtra alfalfa.

Two harvest management systems are being recommended for reduced-lignin alfalfa: Harvest at the bud stage and achieve what for many farmers is higher digestibility (lower lignin and neutral detergent fiber or NDF) than they’ve ever had before, or harvest at early bloom (some recommendations are to harvest first-cutting HarvXtra at 10% bloom) and wind up with higher yields of very good-quality alfalfa.

I can see advantages to both management systems, and there’s no reason a farmer must choose one or the other and be stuck with it. If a farmer intends on harvesting reduced-lignin alfalfa at the bud stage but then something “goes bump in the night” – several days of rain, equipment breakdowns, etc. – the farmer can delay harvest by about a week and still have quality forage. Delaying harvest until early bloom will result in higher per-cutting yields, particularly for the first cut. Higher yields mean additional challenges in getting the mowed crop dry enough for harvest, so managing the forage in wide windrows (at least 70% of cutterbar width) is strongly recommended.

Delaying each harvest until early bloom will often result in similar total yield but with at least one fewer harvest. This has the obvious benefit of reducing labor and equipment costs, but there are two other benefits that may be even more important: less field traffic and better root carbohydrate recovery.

We don’t talk much about the impacts of field traffic on alfalfa plant health, for one reason because until recently there didn’t seem to be much we could do about it. By the time a farmer has harvested a field of alfalfa at least three times, almost every plant in the field has been rolled over by something heavy: tractor, mower, windrower, chopper, etc. This has the potential to damage alfalfa crowns, exposing them to the pathogens that cause root diseases. One fewer harvest per season means less plant damage.

Then there’s the matter of root carbohydrate recovery. Harvesting every cut of alfalfa in the bud stage never allows the plant to fully recover root carbohydrates. Over time, this can weaken the plant and is one reason why alfalfa stands slowly decline in both population and per-plant yield. Root carbohydrate levels will continue to increase until the plant approaches full bloom.

Therefore, modern alfalfa management is a compromise between achieving the forage quality needed by high-producing dairy cows and the nutritional needs of the plant. The University of Wisconsin did a study over several years with a conventional alfalfa variety and found that total alfalfa yields were higher with three cuts than with four cuts. Delaying harvest of most conventional alfalfa varieties until early bloom would result in forage dairy farmers wouldn’t consider good enough for their lactating cows, but with the use of HarvXtra varieties it might be a whole new ballgame.

Since all HarvXtra varieties are also glyphosate-tolerant, farmers wanting to establish a forage grass such as meadow fescue with HarvXtra alfalfa have two choices: Seed the grass with the alfalfa but don’t apply glyphosate (which means paying for a trait they don’t use), or seed the grass anywhere between one day and a week following glyphosate application. (Read the glyphosate label before attempting to do this, and if you have questions check with your state university forage agronomist or regulatory officials.) There’s very little research on “post-seeding” grass into HarvXtra alfalfa, but a few farmers have reported doing so with good results. A key to success with this system is winding up with enough grass but not too much, with “too much” more often the problem.

Feeding reduced-lignin alfalfa

If HarvXtra alfalfa is harvested in the early bloom stage – approximately 40% NDF – it should feed very much the same as conventional alfalfa varieties harvested at the bud stage. Don’t take this for granted, however: Rely on forage analysis to confirm forage quality. If HarvXtra alfalfa is harvested in the bud stage and fed with BMR (brown midrib) corn silage (which is reduced-lignin corn silage), then dairy farmers should work carefully with their nutrition consultants to make sure rations have adequate fiber and other components. We need to keep rates in mind when feeding reduced-lignin alfalfa varieties harvested in the bud stage.

If a farmer isn’t used to feeding this type of alfalfa, it would be prudent to start slowly instead of making it a major part of the ration before he or she has had a chance to see how the cows react. Some folks call this type of alfalfa “rocket fuel for cows.” However, sometimes rockets don’t do exactly what they’re intended to. Better safe than sorry.  end mark

PHOTO: As with any new technology, having it is one thing but learning to use it correctly is another; alfalfa is no exception. Photo by Chris Geralds.

Everett D. Thomas

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