Is there Nitrogen in Snow?

May 2, 2013 04:42 AM

A blanket of post-thaw snow is currently falling over parts of the Midwest from Oklahoma to the Great Lakes. A subscriber asked a question this morning as a joke, but a little research showed that there is nitrogen in snow. In fact, snows before or after the ground has thawed can yield some great benefits to your soil.

As precipitation falls through the atmosphere, it collects atmospheric nitrogen which is in the NH2 form. When snow collects on thawed soil, it slowly melts, allowing a slow-release of NH2 into the soil profile. Conversion to NH3 and nitrate fixing takes place without the microbial paralyzing effects of commercial anhydrous ammonia. Since the ground is already thawed, most of the moisture and nitrogen seep into the soil profile, adding to the total nitrogen content.

Heavy rains and lightning also contain atmospheric nitrogen, but rains heavy enough to contain measurable N generally runoff before nitrogen fixing can take place. Lightning also adds a little of its own, but in very localized pockets where strikes hit the ground.

Of the three, snow is the best form of natural nitrogen. Not only does it allow the necessary chemical reactions to take place in the soil, it also protects micronutrients and bacteria by blanketing the ground. Scientists and old school growers have observed a 5-10lbsN/acre addition from late spring or early fall snow events. This is only a benefit if the soil is not frozen. Most of the nitrogen laced snow that falls on frozen ground will be lost as runoff since the soil cannot soak it in.

So take heart if you are chaining up your loader tractor to move snow here on May 2. Atmospheric nitrogen tends to be high following a dry year suggesting there is N to be had in the snow today. Some will tell you that every cloud has a silver lining. In this case, every spring snow has a nitrogen lining.

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Spell Check

Greenville, SC
1/6/2017 07:44 PM

  Atmospheric nitrogen is in the form N2, not NH2 as this article maintains. While snow could contain atmospheric nitrogen (N2), nitrogen fixation would still have to occur for the nitrogen to be readily available to plants.

Greenville, SC
12/6/2018 08:56 AM

  We are expecting another round of wintry weather tomorrow, and an article in the local paper noted that the snow and bitingly cold weather we have had recently are good for farmers. The cold reduces the population of some pests, particularly the species making their way north. The article also noted that snow contains nitrogen from the atmosphere, providing a little extra boost for lawns come spring. The atmosphere is roughly 80% nitrogen, in the form of N2. The form matters. Nitrogen gas is very unreactive, so much so that it many "air sensitive" materials are packed under pure nitrogen. (The part of the air that is reactive is molecular oxygen, O2.) Snow certainly contains dissolved nitrogen gas. Henry's law predicts the solubility of a gas in a solvent, water in this case, as a function of temperature. It might seem at first glance counter intuitive, but gases are more soluble in cold solvents than in warm (the opposite is true of most solids, as anyone who has tried to dissolve sugar in cold ice tea knows). An inch of snow contains about 7 milligrams of nitrogen gas per square foot, or about 1/3 of a kilogram in an acre of snow. Given that fertilizers are spread onto fields at a field of roughly 300 kilograms per acre, it's not much. The trouble is actually that this nitrogen isn't in a form that easily accessible to plants. Nitrogen in the atmosphere must first be "fixed" or changed into a more reactive form, typically tetravalent nitrogen (ammonium) which is then converted to the nitrate ions that plants can use. So where does the useful sort of nitrogen come from? Industrially, nitrogen is fixed in the Haber process. Since nitrogen is so unreactive, this requires pressures hundreds of times those of earth's atmosphere and temperatures more likely to be found on the surface of Venus (over 700oF). Nitrogen is fixed in the biosphere by microbes, which undertake an elaborate enzymatic dance to do this at low temperatures and pressures

Richard Halterman
Montevideo , MN
5/1/2017 01:18 PM

  As a science teacher painfully misleading article. Atomosheric nitrogen in lightning, no lighting changes atomosheric N2 into more reactive NOx's. The nitrogen on snow is from lightning fixed NOx and from cars and industrial sources. I say it is on snow because as water freezes it repels and pushes other solute molecules out of the lattice. But because water is polar the snow will, attract NOx's to its surface. It will deposit about 1/3 of a kilogram of nitrogen per acre. It still has to be fixed by soil bacteria in a process called nitrogen fixation.


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