Pros & Cons of Using Companion Crops When Planting Alfalfa
Alfalfa often may be seeded with a companion crop like oats to control weeds and erosion and provide a crop of grain or hay. Clear seeding alfalfa alone, without a companion crop, also works well. A preplant herbicide like trifluralin, Balan or Eptam often is sprayed and incorporated first to control weeds in a clear seeding, but a herbicide isn't always necessary. So, which practice should you use?
Your needs and objectives determine whether a companion crop or a clear seeding is better for you. I tend to prefer clear seeding where erosion is unlikely because alfalfa production begins sooner, with 2 to 4 tons possible the seeding year. Companion crops reduce alfalfa yield the first year and often they cause thinner stands. Also, yields and stands in following years almost always are better with a successful clear seeding than when using a companion crop.
In describing oats planted with alfalfa I use the term "companion crop" rather than "nurse crop" because oats don't act like a nurse crop with seedling alfalfa. They act like weeds, robbing alfalfa seedlings of moisture, sunlight, and nutrients during the seeding year. However, on erosive ground a companion crop can be necessary or alfalfa may not start at all.
If you want alfalfa, plant only alfalfa. If erosion is a problem, include about half a bushel of oats with your alfalfa. Then kill oats early using Poast Plus or Select herbicide, or Roundup if your alfalfa is Roundup Ready. The next best option is to hay the oats early rather than taking grain. Likewise, if you want oats, plant only oats. Then seed alfalfa into oat stubble next August if soil moisture is good. Your alfalfa will be better because of it.