Dec. 10, 2010

Manure runoff can result in loss of nutrients and contamination of water bodies receiving the runoff, depending on a number of factors, some of which can be controlled by the producer or applicator. Timing of application, particularly in winter or early spring, and soil or surface conditions should be considered, along with costs.

Conditions that can increase the risk of nutrient loss:

1. Late winter surface application on snow covered, frozen soil on slopes of greater than 5% has the greatest risk of runoff loss.

2. Early winter and spring application may have similar risk of nutrient loss, but less risk compared with late winter application.

3. The risk of loss is generally greater with winter surface application of liquid/slurry compared to solid manure.

4. The risk of nutrient loss is greater with surface application than with injection or incorporation unless incorporation is on highly erodible land.

Conditions that reduce potential runoff loss:

1. Having a longer time from time of application until a runoff event reduces risk of nutrient loss. The risk declines greatly within two weeks of manure contact with non-frozen, moist soil.

2. The risk of loss is generally less with winter surface application of solid manure compared to slurry or liquid manure.

The final decision on when to apply manure needs to balance many factors, some of which are difficult to quantify. The risk of water contamination and nutrient loss needs to be considered with the value and uses of the affected water body, the cost and convenience of time of application, and the risk of soil compaction due to application when soil is wet.

For more information, view a webcast on winter application of manure with Jeffery Lorimor, former Iowa State University extension manure management specialist and researcher.

Charles Wortmann
Nutrient Management Specialist
Charles Shapiro
Soil Scientist - Crop Nutrition