By Randy Pepin
ST. PAUL, Minn. - Application of manure on frozen ground almost guarantees economic loss on the value of manure while also potentially harming the environment. Phosphorus and nitrogen in manure can have negative effects in the environment when in excess.
Phosphorus
Excess phosphorus entering our Minnesota lakes, rivers and streams contributes to eutrophication, which is rapid growth of plant life. This excess plant life eventually dies, and the decaying material causes an oxygen shortage for desirable fish and plant life. We typically observe eutrophication as algae blooms.
A high percentage of the phosphorus in manure is soluble. There is a high environmental risk when this soluble phosphorus is allowed to remain on top of the soil. Phosphorus runoff risk increases with frozen ground, an ice layer on the soil or snow, deep hard-packed snow, and manure applied closer to snowmelt. A snowmelt or rain event allows this soluble phosphorus to dissolve with the water and potentially run off into the environment.
However, when quickly incorporated into the soil after spreading the manure, the soluble phosphorus rapidly attaches to the soil. Once attached, it will essentially only leave the field by plant uptake or with the soil through erosion.
Nitrogen
In general, faster and better manure incorporation means higher nitrogen availability for crops and better economic return from the manure nutrients. When manure is left on the soil surface, most of the nitrogen in ammonia form is lost through volatilization. Many of the organic manure nitrogen compounds are soluble in water and are subject to spring runoff or a rain event, which becomes a contributing factor in eutrophication.
Construction of a long-term storage manure pit is a common method of facilitating spring application and incorporation of manure after the snowmelt and ground thaw on a farm. Pumping the pit in the spring and/or fall and incorporating it into the soil immediately or within 12 hours produces maximum economic return from the manure nutrients while also protecting the environment.
What if a farmer has no pit or has manure packs that can't be added to an existing manure pit? Temporary manure stockpiling is an option approved for most manure management plans.
According to Minnesota feedlot rules, a temporary stockpile must not be in a single location for more than one year and is not allowed on slopes greater than 6 percent. Stockpiling also requires following setback requirements and some common sense. A setback distance of 300 feet is required for most sensitive areas such as wetlands, road ditches and tile-intakes; a 1,000-foot setback is required from most lakes, streams and community water supplies. Stockpiling setback requirements can vary between counties so contact your county feedlot officer or soil and water conservation district staff.
Manure properly stockpiled, later applied on unfrozen ground, and incorporated within 12 hours will typically have higher nutrient content than manure spread on frozen ground, on an ice layer on soil or snow, on deep hard-packed snow, or close to a snowmelt event.
Is a temporary stockpile the best solution to application of manure rather than applying the manure over frozen ground? No, but it is one option to consider.
Get the maximum economic return from the manure nutrients while also protecting the environment by waiting until the ground has thawed to apply manure.
Source: University of Minnesota