A consistent program of applying cow manure to your garden beds will result in a fertile, friable soil. After 10 years in a row of applying cow manure, the soil will still retain up to 20 percent of the nitrogen contained in the cow manure, according to the North Carolina State University Extension. Because it does not contain excessive levels of nitrogen, cow manure will not saturate soils with nitrogen. Chemical fertilizers, on the other hand, contain much more nitrogen than the plants can ever use and the excess is carried away into local watersheds.
Favorable Soil Composition
Nitrogen applied in the form of manure fosters favorable soil microbes, which are indicative of healthy, fertile soil. Manufactured fertilizers infuse the soil with more nitrogen than the plants can use and the excess is washed into rivers and streams. Because cow manure contains organic matter not included in chemical fertilizers, it contributes to improving the soil's structure and water-retaining capacity. Manure also has the ability to improve declining organic soil structure and components, according to the University of Minnesota Extension.
Reduced Soil Erosion
Surface application of cow manure contributes to the improved structure of the soil. It helps to reduce erosion from water run-off similar to that of crops or an applied mulch. The surface-applied manure keeps raindrops from splashing minute soil particles and carrying them away with the rainwater runoff. Chemical fertilizers contain no organic soil amendments and do nothing to improve the structure of the soil.
Reduction of Nitrate Leaching and Runoff
Organic nitrogen applied in the form of cow manure is more stable than manufactured nitrogen applied as part of a chemical fertilizer. Nitrogen in cow manure is released slowly as the soil warms and the crops require it. Commercially manufactured nitrogen is soluble in water and therefore quite mobile. It is easily washed away during rains or other irrigation.
Reduced Energy Demands
Commercially manufactured nitrogen requires high amounts of carbon-based energy to create, primarily natural gas, according to the University of Minnesota Extension. Recycling cow manure by using it to fertilize and improve the structure of the soil uses little to no carbon-based energy.