Pasture and Forage Minute: Winterizing Alfalfa and Grazing Small Grains
Halloween Hay and GDD
Allowing for alfalfa to winterize before dormancy is a key factor preventing winter kill across a stand. Traditionally, my recommendation has been to time the last cutting for roughly six weeks before the first frost. At a minimum, plants need three uninterrupted weeks to complete the transfer of carbohydrates to the crown and roots that is the winterization process. The additional three weeks gives us a cushion in case of an early frost.
While this general guideline has proven its worth over the years, many producers would love to have a bit more accurate method to time last cuttings. One way to narrow the no-harvest window down is by utilizing growing degree days (GDD). Work from the University of Wisconsin calculated winterkill risk looking at GDD at a base 41°F accumulating until a killing frost of 25°F. The two GDD levels of importance for alfalfa stands were 500 and 200.
By providing at least 500 base 41°F GDD after harvest, research trials showed that there was sufficient time for alfalfa to winterize. If harvest occurred with under 200 GDD left, alfalfa plants did not have sufficient time to regrow and deplete carbohydrate reserves to a level that would negatively impact winterization.
While other factors like ground cover and stress of the stand over the course of the year need to factor into the decision for a late cutting, this gives us a more accurate calendar point to shoot for if forage is needed.
As we’ve passed the 500 GDD threshold for most of the state, a tool like the High Plains RCC CLIMOD can be used to look at past years GDD and decide what the risk of getting more than 200 GDD going forward. If chances are low and extra hay is needed, it’s probably safe to take that final cutting.
Fall Grazing Small Grains
If you were able to get a small grain cover crop in early, chances are you’re seeing a fair amount of fall growth now. With forage tight this year, this new forage may be attractive, but do you know the cost of grazing now?
Small grains can be split into two groups: spring and winter species. Winter small grains can withstand cold temperatures after growing this fall, and then will initiate growth next spring. Species like rye, wheat, barley and triticale all have winter varieties. Spring grains on the other hand, are not winter hardy and will not survive the cold. Along with spring varieties of the previous species, we can add oats to the list of spring grains.
Why does this matter? When it comes to fall grazing, spring grains are the big producers. If maintained in a vegetative state, these plants are not trying to translocate energy to the roots to make it through winter — they just grow as much as possible and die. Because of this, quality is maintained, and our best option is to get as much growth as possible before beginning grazing. Studies at UNL have shown oat/brassica mixtures maintaining high protein and energy quality well into January.
For winter small grains, the story is different. These plants are growing now and storing reserves in their roots to survive the winter and initiate growth again next spring. While grazing potential exists, two things need to be considered. First, fall grazing will stop carbohydrate storage and may actually deplete reserves somewhat. This can slow spring green up and reduce overall production next spring. Second, these plants will drop in quality somewhat as temperatures get colder. As energy is moved to the roots, the quality of aboveground growth will decrease. So grazing quality will not be as high mid-winter as earlier in the year.
Small grains make a great fall forage options. Spring grains like oats maintain quality, so shoot for maximum growth before grazing. Winter grains on the other hand need to be grazed with care. Don’t overstress plants and risk yield loss next spring and be ready for a bit lower quality.