Impact on the value of manure, as a fertilizer, when applied to snow
Nitrogen loss from manure applied to snow cover fields.
It was a tough fall for farmers. In many places, Michigan had a persistent wet fall-harvest weather pattern that stretched harvest well into December and even into January. Winter seemed to arrive earlier than it has in the past couple of years forcing many people to apply manure on top of frozen soils or even snow. This leads us to ask the question: What are the impacts on the value of manure as a fertilizer when applied to snow?
When manure is applied to frozen soils or on top of snow, there are two concerning paths of loss for nitrogen. The first concern is surface runoff from the field. When snowmelt cannot seep into the ground, it can carry the manure to low spots or away from the field entirely which may cause environmental issues. Fields with higher amounts of residue are less likely to have runoff as fields with low residue, so this problem may be worse in tilled fields rather than no-till or minimal till systems. Fields that have greater than 2% slopes also have a greater risk of runoff from frozen and snow covered fields into local watersheds. This carries nutrients, like nitrogen, away from your field where it is a valuable resource.
The second method of nitrogen loss we have to consider is ammonia loss through volatilization. Manure has two main forms of nitrogen: organic-nitrogen and ammonium-nitrogen. When ammonium-nitrogen is on the soil surface instead of being mixed in with the soil, it can volatilize and be lost as ammonia gas. While the freezing temperatures slow volatilization if manure is applied below the snow, research suggests it doesn’t stop entirely and ammonia can still be lost to runoff events. With unpredictable freeze-thaw cycles it is difficult to pinpoint how much nitrogen will be lost as the manure sitting on the surface freezes and thaws, too. This is one reason to keep an eye on the extended forecast if you must apply manure on frozen and snow covered ground.
Unfortunately, we cannot estimate exactly how much nitrogen will be lost when manure is applied on frozen soil or snow. Manure nutrient release can vary depending on specific circumstances in your operation and environment. Studies by Kominskey and Lorimor show the amount of nutrients lost on surface applied manures during the winter is highly variable due the extreme fluctuation in weather conditions, with flash events contributing more nutrient loss than slower melt events. Researchers note that it is possible for nearly all loss to occur in a single melt event ranging from 20 -80 percent loss of nitrogen. One way you can manage these losses is by using the EnviroImpact Tool.
It is also important to monitor your crop this upcoming year and be prepared to sidedress additional nitrogen if the crop is looking deficient. The Michigan Right to Farm Generally Accepted Agricultural Management Practices state that you can apply additional nitrogen in emergency situations. Winter application of nutrients is the least desirable in terms of nutrient loss and value of the manure nutrients to your operation. However, Michigan State University Extension understands that sometimes it is a necessary practice, so here are some tips on how to minimize impacts of winter spreading in Michigan: "Manure Management - Spreading on Frozen and Snow Covered Ground (WO1038)" .
Komiskey, M.J., Stuntebeck, T.D., Frame, D.R., Madison, F.W., 2011. Nutrients and sediment in frozen ground runoff from no-till fields receiving liquid-dairy and solid-beef manures. J. Soil Water Conserv.66, 303–312.
Lorimor, J.C., Melvin, J.C., 1996. Nitrogen losses in surface runoff from winter applied manure. Final Report. Univ. Iowa, Ames, Iowa.