Source: Iowa State University, Daniel Andersen
Compliance with regulations
“Familiarize yourself with and adhere to local regulations governing winter manure application,” he said. “Iowa prohibits liquid manure application from confinement operations with more than 500 animal units on snow-covered ground from Dec. 21 to April 1 and frozen ground from Feb. 1 to April 1.”
While solid manure application is not prohibited by Iowa law, careful consideration should be given to minimizing negative impacts on water quality as the state’s waters are protected.
“For a cattle operation, this means that how the law impacts you is dependent on your operation and the manure management system you use. The law doesn’t prohibit manure application if you work with solid manure, like a bedded pack,” Andersen said. “However, all manure applications must prevent water quality violations. Applying from a deep pit or other liquid or slurry manure system will be restricted if you use a deep pit or other liquid or slurry manure system.”
If your facility has an NPDES permit or an NRCS Comprehensive nutrient management plan, be sure to check restrictions specific to your operation in these documents. Typically, both will prohibit winter manure application for all types of manure, both solid and liquid.
The “winter manure application” rules have two parts: a date and condition. Both components must be true for liquid and slurry manure application to be prohibited. So, while the calendar date of Dec. 21 is quickly approaching, it is unlikely that the ground will be snow-covered (defined as 1 inch of snow or 0.5 inches of ice on the soil surface). As a result, liquid manure application would still be allowed until snow cover occurs.
Understanding snow conditions
Applying manure directly onto snow-covered fields poses a significant risk of nutrient runoff when the snow melts, especially if melt will occur quickly. Instead, wait to apply until after snowmelt or choose alternative manure management strategies. Applying manure on frozen ground is also discouraged, as the frozen surface inhibits absorption, increasing runoff potential.
“Timing is key; apply manure when limited snow is present and quick melts aren’t expected,” he said. “Slow melting encourages water infiltration and absorption of manure nutrients into the soil.”
If applying solid manure when snow is present is necessary, choose fields with lesser snow accumulation that are relatively flat. Increase buffer or setback distances around field edges to reduce the risk of nutrient transport from the field.
Thoughtful land use choices
Assessing land use choices is pivotal in winter manure management. Avoid applying manure on steep slopes or areas prone to poor drainage, as these increase the likelihood of runoff. Choose fields with good water-holding capacity to minimize the risk of nutrient loss.
Additionally, consider the implementation of cover crops, which capture excess nutrients and protect the soil from erosion during winter months,” Andersen said. “Residue cover offers these main benefits – it helps hold the soil in place, slows down runoff, reduces erosion, and acts as a filter to help hold dislodged soil and manure particles.”
However, residue can also capture snowfall and hold it in the field. While it takes approximately 10″ of snow to make an inch of water, ice-crusted soil water intake is often slow.
Protecting water quality
Prioritize water quality by maintaining setback distances from water bodies and sensitive areas. Implementing vegetative buffers helps prevent nutrient runoff into waterways. Incorporating manure into the soil soon after application is another effective strategy, reducing the risk of surface runoff and enhancing crop nutrient absorption. Where possible, maintain grass or cover crop buffers downslope of manure-applied areas to slow any runoff and ensure solids in the water settle out before trickling away. Leave a setback area around field borders to reduce the risk of manure nutrients leaving the field.
In conclusion, adopting these best practices for manure application in the winter will enhance nutrient management and contribute to protecting our water resources. While research has consistently shown greater potential risk of nutrient loss from winter manure application, research studies demonstrate loss is often related to quick snow melt or rainfall on frozen soils. Given current Iowa conditions, with no snowpack and low chances of rainfall, the late risk of nutrient loss is lessened this year. Stay informed of the forecast and be proactive to changing weather conditions.
