Does Snow Provide Any Soil Fertility Benefits?

What benefits does snow provide?

Snow has several benefits to growers. It is often referred to as “Poor Farmer’s Fertilizer”, and not only can it contain nitrogen (N), but trace elements as well. There are also other benefits of snow in agricultural systems.

• It can provide over 60% of the annual of precipitation received in northern areas.
• It acts as an insulating blanket. As little as two inches of snow cover can raise the soil temperature above freezing, protecting plants such a winter wheat and alfalfa.
• Snow provides a water source for winter pastured cattle.

How much moisture is in snow?

The amount of water in snow varies depending on several factors. Recent studies suggest that, on average in the Upper Midwest, every 12 inches of snow produces one inch of water (a 12:1 ratio). However, the snow-to-water ratio can change dramatically, even within a single snow event. Some of the variables that influence the ratio include: ¹

• Note that the higher the snow-to-water ratio, the lower the amount of water in the snow.
• The depth of the warm air layer from the surface to the snow producing cloud. The warmer the air is (closer to freezing), the lower the ratio will be.
• The amount of ice in the snow producing cloud. The higher the ratio of ice crystals to supercooled water droplets in the cloud, the less water in the snow.
• Windy conditions can fracture snowflakes, packing them closer together on the ground and leading to lower snow-to-water ratios.
• Deep cold promotes higher snow-to-water ratios.

How much N is in precipitation?

That depends on the location of the precipitation. Generally speaking, the total annual amount of N from all precipitation is about five pounds per acre on the western edge of the Corn Belt and 12 lb/acre on the eastern edge of the Corn Belt. In a single nine-inch snow event in the spring of 2013 in South Dakota, the snow contained about two inches of water and 0.3 lb/acre of available N.²

What forms of N are found in snow?

There are two forms of N found in precipitation, nitrate (from nitrous oxides) and ammonium. Lightning contributes five to 10% of the nitrous oxide, and the remainder comes from human activity such as emissions from automobiles and industrial plants. The ammonium comes from soil microbial activity and volatilization from manure and urea fertilizer. Ammonium can make up from 25 to 75% of the total N in precipitation. The fact that the majority of N in precipitation is the result of human activity explains the higher levels of N in precipitation in the more populated Eastern Corn Belt.²

Can N fertilizer be applied on top of snow, and will it be beneficial?

Research from South Dakota State University found that winter wheat yields were 18% lower when urea was applied on top of snow compared to when urea was applied to bare ground. Similar results have been observed in Kansas. In addition to the negative agronomic impact, applying N to snow or frozen soil increases the chance of run-off, particularly on sloping fields.³

Are there other nutrients in precipitation?

There can be trace amounts of other elements in precipitation. Sodium, potassium, magnesium, calcium, and sulfur are the most common, but the amount of these nutrients is usually so low that they would not have an impact on crop production.⁴

Sources

¹What are snow ratios? National Weather Service. https://www.weather.gov/arx/why_snowratios

²2017. And then it snowed...any free N with that? Farms.com and University of Minnesota Extension. https://m.farms.com/news/and-then-it-snowed-any-free-n-with-that-122181.aspx

³Mengel, D. and Duncan, S. 2008. Surface applications of nitrogen on snow-covered fields of wheat. Kansas State University Extension, Agronomy e-Updates. https://www.agronomy.k-state.edu/documents/eupdates/eupdate011808.pdf

⁴Carroll, D. 1962. Rainwater as a chemical agent of geologic processes—A review. United States Geological Survey, Water-Supply Paper 1535-G. https://pubs.usgs.gov/wsp/1535g/report.pdf

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