Two recent genetic advances in alfalfa breeding are changing farmers’ management of “the queen of forage crops.” The older of these advances, Roundup Ready alfalfa, is genetically modified to be resistant to the herbicide glyphosate. Roundup Ready alfalfa has become very popular wherever alfalfa is grown without a grass companion crop – especially with alfalfa growers in the Western United States – where perennial broadleaf weeds are particularly troublesome. Because the Northeastern United States is the only region where alfalfa-grass mixtures are commonly grown, Roundup Ready alfalfa hasn’t become nearly as popular here as it has elsewhere.
Research at Penn State University investigated some innovative seeding practices where clear Roundup Ready alfalfa was seeded, glyphosate applied postemergence to control emerged weeds, then orchardgrass was seeded across the field. Preliminary results have been encouraging, but this requires an additional trip with the seeder or grain drill, and at a very busy time for farmers. All the seed companies selling Roundup Ready alfalfa also sell “regular” (non-glyphosate resistant) alfalfa varieties, so I don’t sense a big push in the Northeast to sell this type of alfalfa seed. Where farmers do seed clear alfalfa – and in the Northeastern United States about 25 percent of alfalfa is seeded without a grass companion crop – this technology is certainly worth considering. Roundup Ready seed is more expensive because the price includes a technology fee, but seed cost is a relatively small part of the total cost of stand establishment.
A much more recent advance in alfalfa breeding has been the development and release of alfalfa varieties that have less lignin. Lignin is indigestible by dairy cows and other ruminants, so less is more! For the 2016 growing season there will be reduced-lignin alfalfa bred by conventional means as well those with the Roundup Ready gene. A Roundup Ready variety is a GMO and can’t be used in organic alfalfa production systems. Establishment practices, seeding rate and weed control aren’t different than with conventional alfalfa; the difference is in harvest timing. Reduced-lignin varieties accumulate lignin at a slower rate than do normal varieties, so at any stage of maturity – bud, early bloom, etc. the plants contain less lignin and are therefore more highly digestible.
With the reduced lignin variety produced by conventional plant breeding, expect 7 percent to 10 percent less lignin, while the variety with two GMO traits reportedly has 10 percent to 15 percent less lignin. Seed cost of these varieties is higher, and tech fees apply.
Recommended harvest management of reduced-lignin varieties is still a work in progress, with some agronomists recommending delaying the harvest of each cutting until early bloom, while others are suggesting that first cut should still be harvested as normal (in the late bud stage) with subsequent harvests at early bloom. Taking every cut at early bloom would probably result in one fewer harvest per year, but with the same or perhaps higher total yield. However, what if the first cut is harvested at the late bud stage? Fewer harvests with the same or higher yield plus equal or higher forage quality would be a winner because of lower labor and equipment costs. There’s also the advantage in plant health because reduced wheel traffic means less damage to alfalfa crowns.
Grass poses a challenge
Plant breeders have developed reduced-lignin alfalfa varieties, but what about reduced lignin cool-season forage grasses? Unfortunately, not much progress here. Even when seeding conventional alfalfa varieties one of the challenges is finding a grass species (and the variety within the species) that matches well in maturity with the alfalfa. It’s not uncommon for the forage grass to be heading out while the alfalfa is still in the bud stage, so delaying harvest until early bloom would, in many cases, result in fully-headed grass. Therefore, much of what the farmer gains in alfalfa quality he’d likely lose in lower grass quality. There are a couple recently released forage grasses, including one late-maturing orchardgrass (Dividend VL). So far there’s no data on how this grass variety would perform when seeded with a reduced-lignin alfalfa variety. I’m not sold on orchardgrass because of its aggressiveness and iffy digestibility, and also because it’s not as winter-hardy as some other species. But if the new variety is late enough that it matches up well with reduced-lignin alfalfa I may change my mind.
Until we learn more about managing reduced-lignin alfalfa varieties in alfalfa-grass stands, the best idea would be to only plant these varieties in pure stands – no grass at all. If you plant alfalfa with oats or cereal-pea mixtures you could probably use a reduced-lignin variety, though we have no data. But one way to get started with reduced lignin varieties is to plant them on your best alfalfa land, where drainage and fertility is such that straight alfalfa would be expected to do well. Then when you begin harvest, start with the alfalfa-grass stands containing the highest percentage of grass, continuing with your better alfalfa-grass and alfalfa stands, and finally the reduced-lignin fields. (This assumes that once you start harvest, you’ll be able to complete harvest of the reduced-lignin alfalfa before it gets past early bloom.) In a year or two we might be telling farmers that it’s OK to wait until reduced-lignin varieties are at one-quarter bloom for first cut as well, but until we have more field experience a conservative approach is prudent.