Late Fall SublimationAt dawn this Dec. 13, the remote-sensing thermometer showed an outdoor reading of 8.5º F. I think that this is the coldest it’s been in downtown Hartwick in nine months. When the temperature drops this low (or just drops to or below 14º), a meteorological phenomenon takes place that scientists call sublimation. During sublimation, water in the form of ice or snow can evaporate at or below this temperature threshold without having to first go through the liquid phase.

A benefit associated with this occurrence is that when air temperatures descend to this level, water vapor liberated from ice and snow rapidly forms low-hanging cloud cover. This helps seal in Earth’s warmth. Without this cloud shield, much of this geothermal heat would surge into the upper atmosphere due to radiational cooling.

But there’s a negative facet to sublimation: bare soils, lacking cover crop, definitely freeze-dry. This means the affected soils lose moisture. Also, the dried soil particles – especially clays and silts, loosened by freezing/thawing action – are vulnerable to wind and water erosion. The best way to dodge any threat to soil and moisture loss due to sublimation is to minimize the amount of time that the soil lays bare and unprotected. The best way to harness the benefit of expanding ice, so common in freezing/thawing, is to determine the lime needs of fields.

If a soil needs lime, as verified by soil test results, the best time to apply it would be between when I write this column and when the blizzard arrives before most of you read this. The second-best time would be after the blizzard comes, when field conditions permit. In the next few weeks, there will be a lot of freezing/thawing. Such happenings increase the effective neutralizing value of liming materials. Most commercial lime spreaders stress that lime spreads easier with air temperatures over 20º. We should get some of those “warm” spells in the weeks ahead. Let’s plan to take advantage of them.

This freezing/thawing force creates potholes on the roads during winter. Because of its greater volume, thus lower density, ice floats – thus the visible part of an iceberg is only about 10% of its mass. Sometimes I accidentally conduct freezing experimentation with unopened cans of seltzer. I drink seltzer a lot when traveling, because it keeps me hydrated. Ten winters ago, when I wanted to start my pick-up truck on a super-cold morning, I opened the driver’s door only to observe pretty crystalline ice formations on the passenger side interior windshield. I had left a full can of flavored seltzer on the passenger seat and it had frozen. Evidently, just before it froze solid, a hairline crack formed in the can. The remaining liquid, under enormous pressure from the expanding ice, atomized toward the windshield, freezing solid into lovely winter wonderland art patterns.

Attempting to not be beaten by whatever ice winter throws my way, I keep plenty of salt readily available, so as to chase away ice that I can’t get with the snowblower – or even the snow shovel and push broom. These tools move water; they do so by employing physical changes. But salt impacts water’s chemical behavior. The most common salt is sodium chloride (NaCl) or kitchen table salt. A salt is the end product of an acid reacting chemically with a base. NaCl couples with water molecules, reacting with them chemically, yielding two liquids: dilute hydrochloric acid (HCl) in solution and dilute sodium hydroxide (NaOH), also in solution. Dissolved, these compounds take up less volume than the original ice and the original dry salt. The remaining ice crystals restructure with a cracking sound (another chemical change).

Even without the addition of salts, water does some pretty interesting things. We know that with most compounds, as the temperature of the liquid decreases, the density increases as the molecules become more closely packed. But this pattern does not hold true for ice being formed from liquid water – the exact opposite occurs. This is because in liquid water, each water molecule is hydrogen-bonded on average to 3.4 other water molecules. In ice, each molecule is hydrogen-bonded to four other molecules, in a very precise lattice-type structure, very similar to the jacks that some of us older people used to play with when we were children. This means that 100 grams of water at 34º (two degrees above freezing) has a volume of 100 milliliters (ml). When that 100 grams of water becomes ice, it now occupies 110 ml of volume. With limited space, that’s pretty serious crowding amongst the water molecules. This crowding results in enough force to break rigid containers including water lines, engine blocks and unopened cans of seltzer.

We’ve harnessed salt to improve our luck with winter. Now let’s harness winter to improve ruminant diets. Livestock nutritionists refer to heat increment (HI) to include the energy losses associated with digesting food. HI-based energy losses are greater with fibrous foods, like roughages, than with grain and other less fibrous concentrates. In his Feeds and Feeding textbook, Cornell Professor F.B. Morrison wrote “About 33% of the nutrients ingested in corn grain is used in the work of digestion, while this loss is approximately 60% in the case of wheat straw.” These extreme examples of different feedstuffs help us visualize how mammals with different digestive systems, one created to process vegetative (fibrous) materials rather than seeds, can crank out a lot of heat. Cattle, sheep and goats benefit from fiber-based HI in cold weather to keep warm. That frees up the higher quality, less fibrous feeds for other function like making milk and meat.