If Your Alfalfa Winter-Kills

If Your Alfalfa Winter-KillsThe unusually mild months of last November and December concern me about how such benign weather might impact crops like winter forages and perennial alfalfa stands. My cropping confidant, Tom Kilcer, was worried about the matter enough to address the subject in his January 2022 newsletter, “Advanced Ag Systems Crop Soil News” (at advancedagsys.com). As a retired career Extension agronomist and certified crop advisor, Kilcer is well positioned to answer my questions about field crops.

Kilcer wrote that in 2020 he ran an experiment which he and co-workers had conducted for winter-killed alfalfa. The original concept was that as soon as they determined that the stand was lost, growers could no-till red clover, or red clover and oats, to re-establish a forage legume for the next three years. Alfalfa allelopathy, a competition-repelling trait, had no effect on either crop. Another alternative was to no-till just oats and harvest at boot stage in early June, then come back and no-till brown-mid-rib sorghum or sorghum-Sudan for a summer energy crop. It’s harvested in early September, then winter triticale is planted. The winter triticale is harvested for forage and then alfalfa is no-tilled into the triticale stubble to reestablish the alfalfa forage crop.

Quick to admit failure when it does occur, he wrote that they tried the first part of planting oats followed by sorghum. The sorghum crop failed. Quoting Kilcer: “It was a spectacular failure. The sorghum did not grow at all. We speculated that the oats had an allelopathic effect on the sorghum. We strongly suggested not to try this practice. A farmer subsequently told me they had the same failure. To determine if this was a fluke of weather or a real issue, we repeated the study in 2021. We added another variable to the test. After harvesting the oats, for part of the oat plot, we lightly tilled (one to two inches deep) with a disk to break up and incorporated the top inch or two of soil. We then planted the sorghum-Sudan.” He said this time the crop behaved the way it was supposed to.

He explained that where the sorghum was no-tilled into the oat stubble, that summer annual did not grow at all. But a lot of the still-living oats tillered and regrew. The sorghum in the lightly tilled ground, whether in fallow or oat stubble, grew very well with no issues from the oat allelopathy. Quoting Kilcer again, “This solves two problems in one pass with the disk. First and most important, it breaks the allelopathy to allow the sorghum to grow. Second, it is a perfect time to add manure to meet the NPK needs without purchasing more expensive fertilizer. Spreading manure and immediately incorporating will more than triple the amount of nitrogen your crop can get from the manure. It does this without adding excessive phosphorous.” He concluded that this way we can grow the crop on just manure, which is critical in this time of high fertilizer prices. This allows growers to empty the manure storage in early June (Northeast climate region), so they are not pressured to apply it to hay ground in the middle of the growing season.

Sorghum is the perfect setup to be followed by no-till winter triticale for forage. Both will regrow in autumn until the first frost kills the sorghum. The triticale continues to grow and is protected from harsh winter by the dead sorghum stubble which gets flattened by snow. Next spring, we would expect to harvest two to four tons of very high-quality forage dry matter as the first forage cut. Often this yield exceeds what was harvested in the preceding sorghum crop. This practice leaves the field in perfect condition to no-till seed alfalfa in early June after growers have finished harvesting haylage. He writes that they have consistently gotten much better seedings planting at this date by taking advantage of the stubble to keep the small seedlings growing optimally. In other situations, where the triticale was no-tilled into the stubble left behind the harvested sorghum-Sudangrass, this winter forage keeps growing. It benefits from the protection left by the dead summer annual’s stubble; the sorghum has died, still protecting the triticale, then dissipates in spring.

In my own experience, I recall vividly how parts of hay meadows that blow bare of snow can experience major winter kill of alfalfa, particularly clear-seeded stands. All that’s left is grasses that volunteer in. The heaving action associated with the freezing-thawing stress yanks the plant out of the ground. Often the plant’s crown is snapped from its nodules which remain imbedded in the soil. The result: dead alfalfa. I saw such an occurrence demonstrated most graphically back during my service as a field crops Extension agent during the 1970s. At a research farm near Ithaca, a Cornell agronomy professor showed just how alfalfa winter kills.

Robert Seaney, PhD., showed how alfalfa heaves out of the soil if unprotected from the ravages of winter. He had signs posted next to the alfalfa “victims.” One sign read TON (toppled over – necrotic). Another sign read NVP (not very perky). Seaney passed away last year at age 93. Let me quote from a Cornell Ag Life Sciences bulletin: “Seaney worked to identify the best forage species for the state’s soil and climate conditions. He also spent time developing forage management practices that would better support the high productivity of grazing cattle throughout the growing season. As part of his Extension programming, Seaney held tours and field days for cattle producers to learn more about specific techniques.

“For example, Seaney discovered that alfalfa is more likely to survive freeze-and-thaw heaving cycles when it’s mixed into a grassy hay stand, instead of left standing on its own – thanks to the fibrous root networks that act like a shock absorber.” I never forgot that shock absorber analogy. RIP, Bob.

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