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The Upper Midwest experienced remarkably high snowfall this winter. Wisconsin received a staggering 130 inches. Bismarck, ND tallied 101 inches. An early May storm dropped ten more inches in Michigan, disrupting planting. Even for hardy Northerners accustomed to such weather, prolonged winters impact farmers profoundly.
In addition to the delays in field access and deliveries, frantic field work, and modified planting schedules, there are some agronomic considerations that come with a high snowfall year. While quickly melting snow on saturated ground can cause obvious erosion, even a slow melt of these proportions can leach away soluble nutrients like nitrogen (N), sulfur, boron, and potassium. There is no time to get new soil samples, and growers may be second-guessing their plans. Excessive levels of road salt may overload field edges with chloride. Also, what is in snow besides H2O, anything useful?
How Snow Can Benefit Growers
Snow has many well-known benefits on regenerative farms. It insulates and moderates soil temperatures, creating favorable conditions for microbial activity. It protects the roots of overwintering plants from frost heave and keeps soil in place by blocking wind and rain. Deep snow delays weeds from germinating until it is gone, producing a more concentrated flush rather than multiple waves of spring weeds, which can mean fewer and more effective tillage passes. We are now learning that snow forms a slightly gas-enriched environment near the soil surface, slowing loss and enhancing retention of carbon (C) and N from metabolizing soil life below. Snow also brings nitrogen with it from above.
The Impact of Snow on the Nitrogen Cycle
All precipitation contains some nitrogen. Snowflakes’ crystal ice structure encases atmospheric N as they form and flurries it to the ground. This well-studied phenomenon is an important component of Earth’s nitrogen cycle but is rarely considered in agricultural contexts. Maybe because it is unreliable, uncontrollable, and minimal. In a year with 100-plus inches, though, one starts to wonder just how much N does snow contain, and how can we maximize it?
The most common estimate is that from 2 to 12lb per acre of available N may be deposited in an “average” year (whatever that is) but will be more with “high” snowfall. Actual content varies dramatically with complex particulars of constantly changing atmospheric conditions and is hard to predict. Science is appropriately hesitant to mislead us with some handy but wrong back-of-the-napkin calculation.
But we know this: More snow = More N, and fluffy, dry snow holds comparatively less moisture, more air, and thus more N than heavy, wet snow. By observing snowmelt patterns on the landscape, growers may make some practical speculations. North slopes covered for months have time to receive more N than bare south slopes. An unplanted field that suffered meltwater runoff is robbed of fertility. But one with a large melt lasting weeks into a warming spring, with a living crop under it, will have accumulated additional N.
Given the unknowns and the fact that soil’s health, structure, and mineral balance of soils ultimately determine its nitrogen-holding capacity, it’s reasonable to calculate snow-N as part of the biological-N fraction. Microbial fixation is still responsible for the majority of conversion. The snow only brings the N close — an active soil food web must be there to make use of it. This resource is typically lost through runoff and atmospheric loss on poorly managed fields.
After the Snow Melts: Improving Nitrogen Efficiency
To maximize nitrogen from any source, plant and soil systems must have adequate carbon, sulfur, magnesium, and the photosynthetic micronutrients of cobalt and molybdenum.
Carbon sources like humic acids increase nitrogen holding capacity and slowly release it to living things. Cobalt and molybdenum drive nitrogen-fixing enzymatic processes that affect the efficiency of N conversion and uptake. These should be present whenever nitrogen is applied.
Sulfur largely determines soil nitrogen holding capacity, as S:N ratios near 1:10 are required for protein formation. Cool soils are slow to release sulfur from decomposition. Soils that are sandy or low in organic matter, prevalent in the Upper Midwest, are already prone to sulfur deficiency, which may be exacerbated by excessive snowmelt drainage. That’s a lot of impediments to sulfur availability this spring! An elevated S ratio in your starter, especially for corn and canola, may be called for.
After enduring multiple feet of snow this winter, consider what that may have contributed to your nitrogen needs. By employing additional nitrogen efficiency techniques, you can enjoy the added bonus of increased soil health and some free nitrogen.
If you’d like to learn more about how to maximize your nitrogen availability throughout the growing season, visit the Advancing Eco Agriculture website to find more information about our Nitrogen Efficiency Program.