Alfalfa is an important crop for both dry hay and stored forage. However, winter damage can compromise a stand and make it less productive. Al Gahler, ag and natural resources educator in Ohio, discussed winter impacts on alfalfa – the queen of forages.
“One of the main concerns is what stands look like coming out of winter,” said Gahler, who encourages producers to conduct stand counts in spring or autumn. “Dig up a few crowns and taproots in fall to get a good idea of what they look like going into winter.”
In surveying for winter damage in spring, focus on the crown and taproot. Consider stand counts, crown health and heaving. Be aware of cutting management to deal with heaved and unhealthy crowns. Surveying a field also helps assess weed pressure.
“A healthy stand is capable of reaching 100% of its yield potential if there are 50 stems per square foot,” said Gahler. “With 40 stems, yield is down to 80% of maximum yield potential – just from the loss of 10 stems.”
The first evaluation step is counting stems. By the end of April, an alfalfa stand should be in good shape to determine viability and the number of stems per square foot.
To conduct a stand assessment, examine plants in four to five random locations across every 20 acres. Depending on its size, walk the field and do random counts across the entire parcel. Gahler suggests taking a 12-by-12-inch square to the field for accurate counting.
With over 55 stems per square foot, yield won’t be limited. But with 40 to 50 stems per square foot, especially in an older stand, yield may be compromised.
“We typically budget for five-year stands for alfalfa,” said Gahler, “but many farmers push for longer and get six to seven years. If there are at least 40 stems, fields may see yield reduction but are typically still viable.”
Look at crowns to take note of where growth is occurring. As alfalfa plants begin to fail and eventually die, there will be irregular patterns of stems coming out of crowns. Lopsided plants with more growth on one side or in the center and not much on the edges indicate the plant is starting to fail.
“A perfectly healthy crown is very symmetrical and will have healthy stems all the way around and throughout the center,” said Gahler. “The stem count provides more information on yield potential. We want to know how healthy the plants and the stand are to know whether to plan to keep it beyond this year.”
While a stem count indicates the potential for good yield each year, digging down and looking at roots will aid in evaluating root and stand health. The decision whether or not to do a new seeding should be made after looking at both crown and root health.
In doing a plant count, count whole plants. If the stand is newly seeded with 15 to 18 lbs. of seed/acre, there should be 25 to 30 plants per square foot in the seeding year.
Alfalfa – good for livestock, preventing soil erosion, increasing soil nitrogen and carbon sequestration. Photo courtesy of Howard F. Schwartz, Colorado State, Bugwood.org
“After the plant gets through its second winter, there should be four to five plants per square foot,” said Gahler. “That would typically be 55 stems or more per square foot to maintain a healthy stand. If we have fewer than four viable crowns per square foot, it’s time to think about crop rotation – the field is no longer productive enough to be profitable.”
Gahler explained a system that rates plant condition and evaluates winter survival. A rating of 0 is ideal, and describes plants that have a large, symmetrical crown with many shoots. The roots are off-white and have little or no discoloration. In autumn, such observations would indicate plants ready to go through winter.
1 rating – Plants have fewer shoots and a less symmetrical crown. A cross-section of the roots shows signs of discoloration. These plants should still have excellent production and winter survivability.
2 rating – Plants with smaller crowns, poor symmetry and fewer shoots. They may have evidence of crown rot, with vascular discoloration three to four inches deep. These plants are usually aging, but roots still have ample, appropriate off-white coloring and healthy stems.
3 rating – Plants have a weak crown with little or no symmetry, significant crown rot and root discoloration. These plants should be fairly productive this season but may not survive a tough winter with water ponding or numerous freeze/thaw cycles.
4 rating – Plants lack symmetry and have few shoots and significant discoloration. Root rot is present in more than 50% of the root diameter with significant vascular discoloration. Plants probably won’t survive winter, and those that survive won’t be productive.
Gahler said a healthy stand has fewer than 30% of plants with ratings 3 and 4. Such stands should be productive enough to warrant the costs associated with making hay or stored forage and should remain viable after winter.
Heaving is another assessment to make after numerous freeze-thaw cycles. “Look for plants that are abnormally far out of the ground,” said Gahler. “Measure from the ground to the base of the crown. If the base of the crown is more than 1.5 inches out of the ground, it’s likely there are broken taproots and the plant probably won’t survive.”
The higher the crown rises above the ground, the more likely plants will be damaged during cutting and raking. Gahler cautioned producers against rolling the stand in April or May to mitigate heaving because it breaks taproots. Instead, raise the cutter bar to ensure higher cutting that clears heaved crowns.
If there’s an inch or less of heaving, the stand is considered salvageable for the season, but there may be delayed greening next spring.
“We can give the field a chance to survive this season by delaying harvest,” said Gahler. “Push it off to at least 25% bloom, which is mid-June in many places. That allows the plant to settle naturally and push back down into the ground.”
by Sally Colby
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