Ice sheets can smother forage stands

Whether it’s frozen water tanks, slick driveways, or frosted windshields, ice can instigate a number of problems on farms in the winter. While some of these problems are simply solved when the temperature rises, ice sheets may cause long-term damage to forage stands.

In an article from the University of Minnesota, Craig Sheaffer, extension forage agronomist, and Nathan Drewitz and Troy Salzer, extension educators, say ice sheets form in poorly drained areas of a field where standing water from rain or melted snow freezes over. This creates a dangerous environment for dormant forage species.

“Because ice has a high thermal conductivity and is a poor insulator relative to snow, plants can be exposed to low air temperatures, and there is potential for low temperatures to penetrate deep into the soil,” the authors explain. “Even the most winterhardy alfalfa varieties cannot tolerate long-term air temperatures of less than 15°F.”

Ice sheets can also cause plant damage at the cellular level. When ice smothers forage, it disrupts air diffusion and causes carbon dioxide to accumulate beneath the surface. This hinders aerobic respiration and promotes anaerobic respiration, which expends plant energy reserves and generates toxic metabolites in forage like ethanol and lactate.

Damage is variable

The degree of plant damage from ice sheets depends on several factors, including forage species and variety, timing and duration of ice coverage, and plant height. For example, timothy and reed canarygrass are more tolerant to ice coverage than legumes like alfalfa; however, more winterhardy varieties of alfalfa have a better defense against damage from ice sheets than less winterhardy varieties.

Ice coverage is most threatening to forage stands in late winter and early spring when plants are beginning to break dormancy. The longer plants are covered by ice, the more likely they are to become damaged. With that said, different forage species have different ice duration thresholds for damage.

“Some very tolerant grasses like timothy and reed canarygrass have been reported to tolerate as many as eight weeks of ice sheeting,” the authors state. “Legumes like alfalfa and red clover have significant injury after four weeks of coverage.”

Forage stands with sufficient stubble or crop residue are less likely to experience damage from ice sheets as stems and leaves obstruct the ice and allow better air diffusion. Ice thickness may impact plant damage as well.

“No quantitative studies have evaluated ice variables on winter injury, but thicker and solid ice sheets are likely to have more lethal effects on forage stands than those that are thin and porous as a result of mixing with snow,” the authors note.

Tile might help

There’s no way to prevent water from freezing, but there are strategies to limit the damage ice sheets can cause. Install drainage tile in low-lying areas of a landscape to remove standing water from a field and prevent ponding. Additionally, consider seeding forage species that are more tolerant to ice coverage in these poorly drained areas as opposed to alfalfa.

Leave enough stubble or crop residue in forage stands in the fall so plants can poke through ice sheets. The authors suggest seeding a mix of red clover and Italian ryegrass at 10 pounds per acre and 5 pounds per acre, respectively, in parts of a pasture or hayfield that show severe damage from ice sheets in the spring.

Amber Friedrichsen

Amber Friedrichsen served as the 2021 and 2022 Hay & Forage Grower summer editorial intern. She currently attends Iowa State University where she is majoring in agricultural communications and agronomy.