Scientists Study Dairy Cow Manure

Researchers with the Agricultural Research Service say dairy cows that produce USDA-certified organic milk also produce manure that may gradually replenish soil nutrients and potentially reduce the flow of agricultural pollutants to nearby water sources. These cows generally consume forage feeds cultivated on soils that are fertilized with manure and compost rather than manufactured fertilizers. This organic management, in turn, may significantly affect how easily nutrients are converted in soil into forms readily taken up by crops.

Research completed at the ARS New England Plant, Soil, and Water Laboratory in Orono, Maine, and elsewhere, showed that conventional and organic dairy manures from commercial dairy farms differ in concentrations of plant nutrients. They found the two types of manure had at least 17 different chemical forms of phosphorus that varied in concentrations. The organic dairy manure had higher levels of phosphorus, calcium, potassium, manganese, zinc and magnesium.

Organic dairy manure also contained more types of phosphorus found in association with calcium and magnesium. Such forms are comparatively slow to dissolve and would thus gradually release the nutrients. Slow-release fertilizers generally increase the likelihood that they eventually will be taken up by crops, rather than being washed out of fields into nearby surface or groundwater sources.