The Use of Cow Manure for Fertilizer


Cow manure fertilizer contains nitrogen, phosphorous, potassium and other nutrients that plants need, plus it can aerate the soil and help it hold water. Cow manure fertilizers differ from commercial fertilizes in that microorganisms are needed to convert organic nitrogen to inorganic nitrogen that plants can use. It is used both in solid form, incorporated into the soil, and as fluids applied in irrigation water.

Nutrient Availability

The inorganic nitrogen in manure is mostly ammonium (NH4). Most stored manure does not have enough oxygen to turn ammonium into ammonium nitrates (NH3) that plants can use. Ammonia, a form of ammonium nitrate, is lost in volatilization, the process by which solids turn to vapor. The smell of cow manure is the smell of ammonia being lost. Up to half of the available nitrogen can be lost through volatilization. Soil conditions that promote the growth of plants also promote the conversion of organic to inorganic nitrogen. Soils that are dry, cold or water-logged all inhibit the release of nutrients from cow manure fertilizer.


Fertilizer made from cow manure generally contains lower nitrogen than other manures and releases nitrogen more slowly, allowing progressively smaller applications after the first year. The USDA warns against applying too much cow manure fertilizer. Applying too much fertilizer can result in "freezer burn," causing the leaves of plants to turn yellow and the plants to wilt. When this happens, the nitrogen and other nutrients in the fertilizer go unused and leach away. Both solid and liquid cow manure should be quickly plowed under or incorporated into the soil to prevent nitrogen from being lost through volatilization. This will also reduce odors.

Solid Manure

The University of Missouri recommends adding 4 pounds of dry straw to the waste produced by one cow each day. This reduces the moisture content of the mature so that it can be handled as a solid. When cow manure is applied in this way, the micro-organisms that decay the straw consume much of the nitrogen, so that more nitrogen is needed for the plants. You can store manure in a container that has slats or pickets that allow the liquid in the manure to drain off into a holding pond. This allows the manure to be incorporated into the soil as a solid.

Lagoon Manure

Anaerobic bacteria digest cow manure and turn it into a liquid. In the process, the manure is turned into ammonia, carbon dioxide, hydrogen sulfide and methane. Since anaerobic bacteria can live in deep water, anaerobic lagoons are designed to treat water in volume; the amount of surface area doesn’t matter. Anaerobic lagoons produce fertilizer in the form of effluent--liquid waste. Some farmers turn small farm ponds into anaerobic lagoons that can be from 6 to 20 feet deep. The chief disadvantage is the odor they produce.

Slurry Manure

Cow manure stored in containers and mixed with water produces slurry, a liquid fertilizer that can be mixed with irrigation water. The containers may be concrete or steel lined with glass. Slurry containers may be covered or stored in shed or barns. Since less manure comes in contact with the air, it is easier to vent odors. Slurry manure has more concentrated plant nutrients than does fertilizer produced in lagoons. The disadvantage is that slurry operations and equipment for application are more expensive than fertilizer produced in lagoons.


Weed seeds may spread to plants through cow manure. Cow manure can contain from 4 to 5 percent of soluble salts. If you apply too much manure on saline or poorly drained soils, the salts can build up, which is especially harmful to young plants.

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About this Author

Richard Hoyt, the author of 26 mysteries, thrillers and other novels, is a former reporter for Honolulu dailies and writer for "Newsweek" magazine. He taught nonfiction writing and journalism at the university level for 10 years. He holds a Ph.D. in American studies.