Companion crop: friend or foe?

As the winter months grind along, serious forage producers often seek comfort in determining what new varieties of alfalfa they will seed the next spring and where they will be planted. Just as important as the “what” and “where” is the question of “how” alfalfa will be established. Specifically, will a companion crop be used?

Using small grains to establish alfalfa is a long-standing tradition with many forage producers. The advantages of using a companion crop are well documented and include excellent early-season weed control, soil erosion protection, and the opportunity to harvest additional forage in the form of a small-grain crop.

The downside of using a companion crop is it’s always in competition with the alfalfa. The competition is for soil moisture, nutrients and light — the three basic ingredients a plant needs to grow. Therefore, anytime a companion crop is used, the alfalfa stand is compromised.

Companion crops

Let’s first discuss harvesttime of the companion crop. Basically, there are two choices. The small grain can be ensiled or baled from the boot to early heading stages, or it can be harvested for grain in late summer and the straw baled. Removing the companion crop early as silage or hay is clearly the option of choice if only the well-being of the alfalfa stand is considered. By doing so, the competition is removed early in the summer and the original goals of harvesting additional forage, obtaining early-season weed control, and reducing the risk of soil erosion during the establishment phase are achieved. Further, another cutting of alfalfa is available before summer’s end.

What happens if the companion crop is harvested for grain and straw? For the underseeded alfalfa stand, only bad things can happen from mid- to late summer. These include:

• severe moisture and light competition

• lodging of the small grain and subsequent smothering of the alfalfa plants

• insect infestations (potato leafhopper) that injure or kill alfalfa plants — usually is undetected and untreated because of the standing small-grain crop

• smothering of alfalfa plants if straw windrows are left in the field too long after grain harvest

• significant competition from volunteer cereal grass growth after the small-grain harvest

Many seeding-year alfalfa stands have been lost from one or a combination of these factors. As a result, there are thankfully far fewer alfalfa stands established following a cereal grain harvest than was the case 20 years ago. If a companion crop is intended for grain harvest, an early maturing, stiff-strawed variety is recommended.

For many years it was difficult to establish pure alfalfa stands without the use of a companion crop. Today, with the availability of several selective post-emerge herbicides, it is done with regularity on a variety of soil types. For many dairy producers, harvesting small-grain silage seems to be more of a chore than a welcomed forage source. Small-grain silage often causes headaches from the standpoint of separating the silage from other high-moisture forage inventories. This seems especially true for producers harvesting more corn silage. Direct seedings of alfalfa offer the advantages of harvesting more high-quality alfalfa during the establishment year and increasing overall whole-farm alfalfa dry matter yields.

Rankin is a University of Wisconsin Extension crops and soils agent.

This article published in the January, 2010 edition of WALLACES FARMER.

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