Why Separate Dairy Manure?
April 5, 2000 ISSUE #M5
The use of manure separators is practically unknown in many areas, while in other regions no dairy is without a device of some sort. There are reasons why this is true, and it is equally true that the trend is toward the expanded use of manure separators.
There are different justifications for the use of manure separators. Probably the strongest reason is to keep solids out of the manure ponds and to get the manure solids into a form that can be land applied without building a cake layer on the pasture or field. If un-separated manure is sent to the pond, tank or Slurrystore structure, settling can become a problem. This is especially true in flush barn ponds where a source of clarified water is requisite. The repeated cost of dredging a pond can be sufficient to justify installation of a separator.
Spraying the raw manure on a field or pasture is not a foolproof alternative. Flush barn farms usually need the recycled water. Besides, the wet manure can build up a mat layer so dense that grass will not grow through it. In contrast, composted manure solids are readily tilled into the soil, with strong benefits from fertilizer and organic addition.
There are areas where an altogether other justification exists for using a manure separator. Many farmers, especially in the north central States, use the composted manure as bedding for their cows. This represents a direct savings of cash that would be spent on sawdust, sand, ground paper, straw, or other bedding. (Farmers in other areas fear that, because of the climate, disease outbreak may occur with the use of manure bedding, so the practice is not used among them.)
Many other reasons are given for using a manure separator. In every county there is the story of the farmer who is getting rich raising worms in the compost, selling potting soil to nurseries, or selling bags of compost for $4.00 each. There is less discussion of the practice of blending press cake (which is mostly undigested feed, 50% protein) in the ratio of 5% for heifer and non-lactating cow ration.
Odor reduction is probably the greatest fringe benefit of using a manure press. However, environmental regulations have not reached the point of mandating the use of these machines.