Alfalfa, a perennial legume used mainly as high-quality feed for cattle, horses, sheep and goats, is high in protein (16-20% crude protein) and contains a lot of calcium and other minerals and vitamins.
On the other hand, alfalfa faces a cold challenge. In the U.S., alfalfa is grown mainly in western and northern states. The cold winters and other factors in many of these states can damage alfalfa crops, which can lead to losses for farmers and forage shortages, according to an announcement from the American Society of Agronomy.
Researchers at the University of Minnesota are working to help farmers offset losses caused by alfalfa winterkill. They are trying to identify annual forage crops that can be cultivated in fields with winter-killed or terminated alfalfa.
"Planting annual forage crops into terminated alfalfa is an economically viable strategy in response to alfalfa winterkill," University of Minnesota extension specialist M. Scott Wells explained.
However, net economic returns can vary depending on which forage crop is planted. Different forage crops have different characteristics, including yield, nutritive value, tolerance to frequent cutting and whether they can take root and grow efficiently.
Wells and his colleagues identified annual ryegrass as the forage crop with the highest net returns when planted into terminated alfalfa in Minnesota test sites, the announcement said.
Finding forage crops that can help farmers offset losses due to alfalfa winterkill will have widespread benefits. In 2013, 93% of alfalfa growers surveyed in Wisconsin and Minnesota reported alfalfa winterkill or injury. Many reported alfalfa losses that were greater than 60%.
Why not simply re-plant alfalfa into the killed or injured alfalfa stands? Older alfalfa plants release chemicals that can reduce the productivity of newly seeded alfalfa and, in some cases, kill the new stands. "Even if the alfalfa plants do live, there is a chance the plants will be less productive," Wells said. "It's best to rotate to silage or a small grain forage crop."
The researchers grew seven different forage crops on terminated alfalfa. They also tested a mixture of annual ryegrass and red clover. They measured yield, nutritive value, how the crops were affected by nitrogen fertilizer and economic viability.
The study found that the highest-yielding forage crops didn't necessarily have the highest economic returns. For example, teff (a grain) and Sudangrass often had the highest yields, but they also provided reduced nutritive values, which lowered their economic returns.
On the other end of the spectrum was annual ryegrass, with high yields and high nutritive value. It also established consistently across study sites and years.
"Our work suggests that annual ryegrass is the most reliable and economically viable option to providing early-season forage with alfalfa winterkill," Wells said.
The researchers also tested whether applying nitrogen fertilizer increased economic returns. In general, it didn't. At study sites, nitrogen from terminated alfalfa was often enough to meet the needs of the forage crops. Applying nitrogen fertilizer usually didn't lead to increases in economic returns.