Using Manure in the Home Garden

Manure is a valuable soil amendment for home gardens. It not only supplies macro and micronutrients for plant growth, but also is a source of organic matter. Increasing soil organic matter improves soil tilth, increases the water holding capacity of sandy soils, improves drainage in clay soils, provides a source of slow release nutrients, and promotes growth of earthworms and other beneficial soil organisms.

Proper use of manure will ensure that your plants will be supplied with adequate nutrients and that your soil tilth will improve. Too low a rate of applied manure can lead to nutrient deficiency and poor plant growth. On the other hand, too high a rate can lead to nitrate leaching, nutrient runoff, excessive vegetative growth and, for some manures, salt damage. It is important to understand that manure characteristics can vary greatly with animal, bedding, storage, and processing. Because of this variation, the recommended rates provided in this report should be considered as very general.

Fresh manure

Characteristics of fresh manure include high amounts of ammonium or soluble nitrogen resulting in a higher available nitrogen content compared to composted manure. Salts in fresh manure also tend to be high - especially in poultry/turkey manure. Fresh manure may contain high amounts of viable weed seeds, which can lead to a weed problem. Because of the high amounts of ammonia-nitrogen in fresh manure, it should be incorporated 6 to 8 inches within 12 hours after application. Without incorporation much of the soluble nitrogen will be lost to the atmosphere as ammonia. To avoid salt damage, seeding operations should not be done until 3 to 4 weeks after application. Type of bedding or litter will usually decrease manure nutrient content by dilution. If straw or sawdust is used, nitrogen availability may be lowered by increasing the C/N ratio. High carbon relative to nitrogen (greater than 25 /1) will tie up nitrogen.

Composted manure

Composting manure will lower the amount of soluble nitrogen forms by stabilizing the nitrogen in larger organic humus like compounds. Some of the ammonium-nitrogen will be lost as a gas during composting. Heat generated during the composting process will kill most weed seeds. Composted manure has lower availability of nitrogen and will contribute more to the organic matter content of the soil compared to fresh manure. Unless applied at high rates, composted manure alone may not be able to supply all the nutrients for fast growing plants. Since soluble nitrogen is not high in composted manure, immediate incorporation is not critical; however, to obtain full benefit from the compost, incorporation to a depth of 6 to 8 inches is recommended whenever possible.

Nutrient availability

The analysis of manure or compost provides total nutrient content; however, availability of the nutrients from the manure for plant growth will depend on the breakdown and release from of the organic components. Generally, 70 to 80% of the phosphorus and 80 to 90% of the potassium will be available from manure the first year after application. Calculating nitrogen availability is more complex than for phosphorus and potassium. Most of the nitrogen in manure is in the organic form. This form is considered unavailable for uptake until it is broken down to soluble forms by microorganisms. A smaller fraction of the nitrogen in manure is in the ammonium/ammonia form and is considered immediately available for plant growth. In most cases, manure application is based on its nitrogen content and estimated availability for the first growing season - see table below. It should be remembered that some manure contains high levels of phosphorus, so while plant nitrogen demands are met, soil levels of phosphorus may be building up. Use of soil tests will help in determining the level of phosphorus in the soil as well as the need for further applications.

Suggested rates of manure or compost to apply on a fresh weight basis to supply about 0.2 lb of available nitrogen per 100 square feet.

Note: one 5 gallon bucket holds about 25 lbs of fresh manure or compost.

– Carl Rosen, University of Minnesota Extension Soil Scientist. Article from the University of Minnesota's Yard & Garden Line News, Volume 1 Number 4,  June 1, 1999.

Additional Information:

• Composting Livestock Manure: Using Composted Livestock Manure Safely in the Garden – Washington State University MG's Stewardship Gardening
• Manure – on The Gardener's Network

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