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Variety Selection
Plant breeders have developed alfalfa varieties with greater yield potential and disease resistance and improved forage quality. But with over 250 varieties available, how does one select an alfalfa variety? The major factors leading to profitability are:
1. yield potential,
2. persistence (percent stand remaining or estimated from
winter hardiness and disease resistance ratings),
3. winter hardiness,
4. disease resistance, and
5. forage quality.
As illustrated in table 1, yield has the largest effect on profitability, persistence next, and other factors have a lesser effect.
Yield potential
Look for varieties with high yields in university trials. Compare new varieties to Vernal, a winter hardy check variety. Comparing varieties to the same check, planted within the trial, also allows comparison across several trials. New varieties should perform better than Vernal. In Wisconsin and Minnesota variety trials over the last 10 years, the top varieties have yielded up to 0.89 tons more per acre than Vernal for each year of stand life (figure 4). For short-term stands, select varieties by yield from 2- to 3-year-old stands. For long-term stands, select by yield from 4- to 5-year-old stands.
Varieties will perform differently in various growing regions. Look for top yields of a variety grown in a site with as similar a soil type and climate to your farm as possible. Also, look for top yield over several sites. This indicates stability for high yield and is important because soils may vary on your farm and weather conditions change from year to year.
Persistence
Compare stand survival ratings or yields of 4- to 5-year-old stands to determine relative persistence of varieties. Persistence in northern locations is most dependent on winter hardiness because of the severity of winter temperatures (figure 5), while farther south persistence is more dependent on disease resistance levels. In the absence of stand survival ratings or yields of 4- to 5-year-old stands, use winter hardiness and disease resistance to estimate persistence.
Winter hardiness
Winter hardiness is dependent on cold tolerance, fall dormancy, and resistance to root and crown diseases. Lack of winter hardiness may result in winter injury and winterkill. Winter injury slows spring growth meaning fewer shoots for first cutting and a lower yield. The best indicator of winter hardiness is stand survival ratings (count of live plants) the spring following a severe winter.
Generally, varieties with less winter hardiness have greater yield potential because of faster regrowth. Planting several fields of alfalfa, each with different winter hardiness ratings ensures stand survival of some fields in severe winters and increases yield potential in others.
Disease resistance
Diseases may cause seedling death, reduce stand density, lower yields, and shorten stand life. The best disease management strategy is to select varieties with high levels of disease resistance. Determine potential for diseases on your farm and select alfalfa varieties with resistance to as many of them as possible. Knowing which diseases have occurred in your fields will help you choose varieties with the appropriate resistance. Look over the descriptions and pictures in the disease section of this booklet, learn to recognize them and select resistant varieties if the disease is occurring in your field. To estimate the potential for each disease to occur in your area, refer to the maps in the disease management section.
Forage quality
Many new varieties coming on the market have improved forage quality. Evaluate alfalfa varieties based on estimated digestibility, intake and relative feed value compared to Vernal, the standard variety.
Intended use
Most alfalfa is planted for harvest as hay or haylage with plans to keep stands as long as they are productive. Special situations may require different variety selection criteria. For example, when a short rotation is desired or when nitrogen for other crops is needed, yield is more important than persistence so select varieties with high yields in the first two years; when the field will be used for grazing, select grazing-tolerant varieties.
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