Advances in Alfalfa Breeding

The impacts of alfalfa variety improvements – forage yield and quality – have paled compared with those of other field crops.

In February’s issue, I discussed a new advance in alfalfa breeding – reduced-lignin alfalfa – stating it was too soon to know how much impact this will have on farmers’ forage production practices. We now have another growing season’s experience plus several years of university research, and the results are very encouraging. It looks like reduced-lignin alfalfa is the “real deal.”

The impacts of alfalfa variety improvements – forage yield and quality – have paled compared with those of other field crops. National yield trends for alfalfa have been discouraging, especially compared with remarkable increases in corn and soybean yields. The most notable improvements in alfalfa breeding were in disease resistance, and almost all modern varieties are now resistant to several common alfalfa diseases.

However, resistance to a disease is important only if the bacteria or mold spores causing the disease are present, and, in many cases, they aren’t. That’s why university variety trials often find only modest yield differences between alfalfa varieties with little or no disease resistance and those with resistance to as many as five diseases. Further reducing the influence of disease resistance: Farmers’ crop rotation schedules are such that by the time the alfalfa plant is infected by, for instance, Verticillium wilt disease, the field is scheduled to be plowed up and planted to a row crop such as corn.

Past efforts at improving alfalfa quality

Genetic improvements in alfalfa quality have been harder to accomplish. Until recently, improvements in forage quality have almost always been at the expense of yield. Farmers wanting higher alfalfa quality achieved it only by more intensive harvest management – for instance, mowing at the bud stage instead of at early bloom. This improves forage quality but interferes with the plant’s carbohydrate storage, increasing the likelihood of reduced yields and increased winterkill. The more times each season that alfalfa is harvested before the plant has had enough time to accumulate carbohydrates, the more impact there is on the yield and plant health.

One challenge of increasing alfalfa quality is the plant’s lignin content, which is indigestible and an “anti-quality” factor. Reducing alfalfa’s lignin content can negatively affect standability, making machine harvest very difficult. Many years ago we planted an alfalfa variety at Miner Institute promoted as having fine stems and high forage quality. It did have these things, but we discovered the higher quality was at the expense of standability; every cutting lodged, and we wound up leaving a large amount of alfalfa in the field.

Reduced-lignin alfalfa

Enter reduced-lignin alfalfa, the first advancement in alfalfa forage quality not at the expense of yield or stand life. University research is finding that the harvest schedule recommended for reduced-lignin alfalfa is increasing yields while positively impacting root carbohydrates. These new varieties allow farmers to delay harvest by about a week, from late bud to early bloom stage. During this week the alfalfa continues to grow, thereby increasing yield and also storing more nutrients in the taproot. This results in faster regrowth following harvest, with the resulting increase in yield, and also may allow the plant to enter winter with more root carbohydrates, improving winter survival.

In the past generation we’ve seen an increase in intensity of alfalfa harvest management: Following first harvest, farmers typically mow alfalfa every 30 to 35 days, or several days to a week less than in the past. In much of the northeastern U.S. and eastern Canada this has resulted in alfalfa being harvested four times per season instead of three. In some years, especially in areas with a longer growing season, five cuts are possible. This management system can result in a farmer never seeing a blossom on his alfalfa plants – from seeding to rotating the field to a different crop.

But on many farms, planting reduced-lignin alfalfa and then delaying harvest will result in one fewer harvest per season. Is this a step backwards? No – not if planting reduced-lignin alfalfa also results in higher yield and better forage quality! Four years of research at the University of Wisconsin found 15 to 20 percent higher yields with a three-cut system using reduced-lignin alfalfa versus a four-cut system using a conventional variety.

There’s another short- and medium-term advantage to one fewer harvest per season (not long-term because farmers seldom leave alfalfa fields in production for more than five years – and even reduced-lignin alfalfa probably won’t change this). Making one fewer harvest has an immediate economic advantage because it means one less trip with the mower, rake or merger, and chopper or baler. The combined reduction in equipment and labor cost is significant. Short- and medium-term impact is due to less damage to alfalfa plants – short-term impact to the forage itself and medium-term impact for the plant crowns.

Over the years I’ve dug up a lot of alfalfa plants in established fields and have been amazed at the amount of damage including cracked crowns and root rots. Our research at Miner Institute also showed a single pass with a heavy farm implement tire reduced alfalfa yield (of those plants) in the next harvest by over 40 percent.

Finally, reduced-lignin alfalfa may simply free up time. Many farms don’t have time to harvest all first-cut grass before alfalfa is ready to harvest. A week’s delay in alfalfa harvest gives farmers more time to mow first-cut grass, plant corn, spray crops – anything that usually needs to be done in May.