On the morning of Dec. 23, our remote-sensing thermometer had just climbed up to 0º, having plunged to -7º a few hours earlier under a half-moon in a clear sky. There’s a good chance that night would prove to be the coldest one in 2024.
In the preceding 48 hours, downtown Hartwick accrued about five inches of snow, including some lake effect snow. Not bountiful snow cover, but adequate. Without sufficient snow cover, Medicago sativa (alfalfa) is prone to heaving, particularly on less than ideally drained soils.
Heaving is caused by the freezing-then-thawing stress of expanding/contracting soils. Years back, during my agronomy Cooperative Extension career, Cornell Field Crops Professor Bob Seaney explained how a companion grass protected alfalfa from heaving damage. He showed how the fibrous root system of grasses, particularly timothy, provided a shock absorber benefit which countered expanding soils as they yanked against the nodule-laden alfalfa roots.
Sometimes alfalfa enters winter with more soil moisture than normal. This water abundance increases chances for frost-heaving injury. Just as paved streets can heave and settle in winter due to freezes, so can alfalfa plants. This heaving action may be strong enough to snap taproots. Sometimes the alfalfa completely moves with the soil; in other situations, the alfalfa does not completely settle back down, especially when the taproots are snapped. When this happens, the crown is exposed above the soil surface. If this happens too early in winter, the exposed crown tissue will be killed by cold temperatures. Should such happen later enough in winter/spring, the exposed crown may still survive for another season, provided the cutting height is above the crown. However, the plant will likely winter-kill next winter when the raised crown is exposed to cold weather ravages.
A useful measure of winter’s severity is the soil temperature taken four inches down into topsoil. In temperate climates, these readings in winter are usually in the upper 20s to low 30s. Joshua Michel, Extension field agronomist in northeast Iowa, observed during 2023, “These temperatures typically are of little threat to alfalfa crowns as long as we maintain adequate snow cover. This protection from nature provides an insulation factor, which can counter below-zero air temperatures. A lack of snow cover during periods of frigid air temperatures can be very stressful for overwintering plants. A couple of very cold days in December and February [2022 and 2023] caused four-inch soil temperatures to drop down to as low as 13º F at some weather station locations across northern Iowa. It will likely become obvious as fields begin to green up where the snow drifted and provided insulation, compared to parts of a field that may not have been protected.”
Alfalfa – good for livestock, preventing soil erosion, increasing soil nitrogen and carbon sequestration. Photo courtesy of Howard F. Schwartz, Colorado State, Bugwood.org
Back in the Northeast, I’ll tap into the wisdom of Certified Crop Advisor Tom Kilcer. For decades Kilcer oversaw field operations at Cornell’s Valatie Research Farm in Columbia County, NY. In his online newsletter at advancedagsys.com, Kilcer wrote that in 2020 he conducted experiments assessing winter-kill alfalfa damage. Making the best of a bad situation, the original concept was that as soon as it was determined that the stand was dead or nearly dead, growers could no-till red clover (or red clover with oats) to re-establish a forage legume for the next three years. The dying (or dead) alfalfa’s allelopathy had no effect on either crop.
Let’s define allelopathy: “The chemical inhibition of one plant – or other organism – by another to the release into the environment of substances acting as germination or growth inhibitors.”
Into this dead alfalfa sod in 2020, they planted oats followed by sorghum. Kilcer wrote, “This approach was 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 incorporate the top inch or two of soil.”
Next they planted the brown midrib (BMR) sorghum/sudangrass (SS). The SS in the fallow ground grew fine. The SS no-tilled into oat stubble did not grow at all, due to allelopathy. In the lightly tilled ground, whether in fallow or in oat stubble, SS grew very well, with no issues from oat allelopathy.
Kilcer stressed, “This solves two problems in one pass with the disk. First and most important, it breaks the allelopathy to allow sorghum to grow. Second, it is a perfect time to add manure to meet 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 manure. It does this without adding excessive phosphorus.” This allows growers to empty manure storage in early June so they’re not pressured to spread on hay ground during growing season.
Sorghum is handily followed by no-till winter forage triticale. Both crops grow in autumn until the first frost kills sorghum. Triticale continues growing, protected from winter’s harshness by dead sorghum trash, which is usually flattened by snow. Come spring, expect two to four tons dry matter/acre of high-quality forage – better than BMR SS – as the first cutting. This practice leaves the field in ideal condition to no-till alfalfa (or red clover) seed in early June after harvesting triticale haylage.
Kilcer said they have consistently gotten much better seedings by planting them at this date, using stubble to keep the small seedlings growing optimally.
It’s important how photosynthetic energy is stored in plants. In alfalfa, energy is stored as cellular starch. Alfalfa has 92% more starch than clover. But clover has higher sugar than M. sativa – 87% more.
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