(the following information is courtesy of Purdue University and Washington State University Cooperative Extension)
The benefits of manure are widely misunderstood. Many gardeners value it only as a fertilizer. As a source of primary nutrients, though, manure offers much less pound for pound than a bag of inorganic fertilizer. So what are its benefits?
First, manure does contain the primary nutrients - nitrogen, phosphate, and potash - but in small amounts. For example, you would need 8 times as much horse manure as 5-10-10 fertilizer to supply a given amount of nitrogen. If you rely on manure to supply primary nutrients, you'll need a pile, literally. Most gardeners supplement manure with other fertilizers.
Primary nutrients don't supply all of a plant's needs, though. Secondary elements, sulphur,calcium, and magnesium,are required in substantial amounts. Micronutrients, including zinc, boron, iron, and copper, are also needed in minute quantities. Manures are usually an excellent source of these elements.
Not only does manure supply nutrients, it helps hold them in the soil. Particles of humus derived from manure carry a negative electrical charge which allows them to combine with many plant nutrients that carry a positive electrical charge. Sand is electrically neutral, which explains why it doesn't hold nutrients well. Adding manure to sandy soil greatly enhances that soil's ability to catch and store nutrients.
The most important benefit of manure is as a soil conditioner. Mixing manure into a sandy soil is like introducing thousands of tiny sponges that help retain moisture. Manure also helps loosen and aerify a compacted clay soil.
Manures also transport useful microbial hitchhikers. These living components of organic matter manufacture glues that cement soil particles into crumbs. Crumbly soil is ideal as far as most plants are concerned because its structure allows it to hold both air and water.
Once dissolved in water, most inorganic fertilizers are quickly available to plants. But slow release fertilizers like manure are also beneficial because they provide small amounts of nutrients over several years. If you apply some manure each year, you'll maintain a small reserve of nutrients plants can draw on throughout their growing period.
Manure does have some drawbacks though. When fresh, it may contain weed seeds. You can minimize the problem by rapid composting. The heat generated in a quick pile will destroy most of weed seeds.
Some manure, such as chicken, can generate penetrating, nasty odors, but by applying them in winter or early spring they'll be less volatile.
Do not put manure from dogs, cats, and pigs in your food garden. They can carry disease organisms and parasites that can be transmitted to humans. Other precautions must also be taken to use livestock manure safely. Finally, it may be difficult to locate a cheap source of manure and transport it to your garden.
If you have access to a plentiful source, fresh manure can be applied at a rate of about 450 pounds per 1,000 square feet in the fall or winter. Composted manure can be applied anytime in a layer 1" to 2" deep and tilled into the soil. Use half these rates for poultry, rabbit, and sheep manures, which are more potent. You still may need to add phosphate and potash fertilizers since most manures don't provide sufficient amounts of all nutrients. A soil test will indicate if these are needed.
Gardeners interested in building a superior soil and stocking it with slow release nutrients would do well to prospect for "brown gold".
by Van Bobbitt, Master Community Horticulture Coordinator & Dr. Val Hillers, Food Specialist, Washington State University Cooperative Extension
Pathogens (microorganisms which cause disease) can be transferred from animal manures to humans. The pathogens Salmonella, Listeria and E.coli , as well as parasites, such as roundworms and tapeworms, have been linked to applications of manure to gardens.
Publicity about illnesses due to E.coli 0157:H7 has made people more aware of the potential risk of foodborne illness from manure contamination. As a result, many are now asking whether it is safe to use manure on their gardens.
In August 1993, The Lancet Medical Journal reported on a small E.coli 0157:H7 outbreak that appeared to be the result of manure applications to a garden. The gardener ate eggs and milk products, but no meat, and her diet relied heavily on vegetables from her garden. She fertilized the garden all summer with manure from her cow and calf. No E.coli 0157:H7 bacteria were isolated from fecal samples taken from the cow and calf; however, the animals did have antibody counts for the pathogen, suggesting they had been previously infected. E.coli 0157:H7 was isolated from the manured garden soil.
So, how risky is the use of manure in gardens and compost piles? If you use fresh manure in the garden, there is a small risk that pathogens which cause disease may contaminate garden vegetables. The risk is greatest for root crops, like radishes and carrots, and leafy vegetables, such as lettuce, where the edible part touches the soil. Careful washing and/or peeling will remove most of the pathogens responsible for the disease. Thorough cooking is even more effective.
To reduce the risk of disease, we suggest these precautions:
Apply fresh manure at least 60 days before harvesting of any garden vegetables which will be eaten without cooking. If you apply manure within 60 days of harvest, use only aged or composted manure.
Never apply fresh manure after the garden is planted.
Thoroughly wash raw vegetables before eating.
Do not use cat, dog or pig manure in gardens or compost piles, because some of the parasites which can be found in these manures may survive and remain infectious for people.
People who are especially susceptible to foodborne illnesses should avoid eating uncooked vegetables from manured gardens. Those who face special risks from foodborne illness include pregnant women, very young children, and persons with chronic diseases, such as cancer, kidney failure, liver disease, diabetes or AIDS.