– Robert Meinen, Senior Extension Associate, Penn State University
At this time of year you may be looking at a full manure storage and desire to get an early jump on application for the coming growing season. Patience can pay off in the form of manure nutrient conservation. After all, the goal of manure application is to place valuable nutrients on the soil where they are needed and to keep them there. A large part of this equation is timing. The closer the nutrient is applied to actual crop need the better.
The goal of manure application is to place valuable nutrients on the soil where they are needed and to keep them there.
Application of nutrients during times of snow-cover, frozen soil, or saturated conditions increases risk of nutrient loss. Once a nutrient passes the field edge it is lost to the environment – and lost from crop uptake. A fraction of both nitrogen and phosphorus in manure will be present in soluble forms. If the liquid solution of manure can infiltrate the soil then soluble nutrients will infiltrate with the liquid to a location that is safe from overland runoff. The ammonium nitrogen fraction will also be safe from volatilization after it is beneath the soil surface. Frozen, snow-covered, and saturated soil conditions hinder infiltration. Spring rain events can carry both the soluble and solid portions of manure from the field.
If you must apply manure before conditions are ideal, you should go to fields specifically listed in your nutrient or manure management plan to receive manure during the current season. Some things that limit risk of manure nutrient loss include fields with shallow slopes, fields with a perennial crop such as hay, fields with a cover crop, fields with lots of crop residue, and fields that are more distant to water. You should prioritize the order of manure application according to risk and go to the least risky fields first.
Because infiltration can be limited at this time of year, extreme runoff events can occur. For instance, snow melt or rain on frozen or snow-covered ground can cause runoff to occur from lands that rarely lose water. For this reason, it is wise to skip subtle swales in these fields where water can gather and flow. Nutrients placed here certainly won’t stick around. These shallow depressions can be covered with manure later in the spring when risk is lower. Pay attention to the weather forecast, and avoid situations where you expect upcoming weather may undo the nutrient placement work you have done.