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    Curtis E. Swift, Ph.D.
    Colorado State University Extension
    Tri River Area


    There are Salts in Manure
    The Texture of Manure & its Effect on Soil
    Salts & Composted Manure
    Manure & Human Pathogens
    Antibiotics are Taken up by Plants from Manure
    Runoff and Edible Crops
    Manure Tea
    Using Pet Feces in the Garden

    The Salt Level of Manure
    Manures contain salts and may increase the soil salt level when used as mulch or soil amendments. This elevated salt level can be a serious problem when the resulting soil salt level is greater than the salt tolerance of the plant. This is likely to occur when the soil is already on the border line of salt tolerance of the plants being grown.

    A survey of 156 manure samples collected in 1996 throughout Colorado indicated manures had salt levels from 3.3 mmhos/cm3 to a high of 42.8 mmhos/cm3. Many vegetable crops have salt tolerances between 1.5 mmhos/cm3 and 4 mmhos/cm3 and when high salt manures are used around these plants, severe damage can occur. Grasses, flowers, trees and shrubs also have specific salt tolerances above which they can not tolerate. Further information on plants and their salt tolerance is available.

    Following are the results of the Colorado State University manure survey:

    Electrical conductivity of manure samples in Colorado Manure Source Average EC (mmhos/cm3) Minimum Maximum
    Beef 28.2 8.4 42.5
    Horse 6.2 3.3 10.2
    Sheep 23.4 9.4 42.8
    Chicken 23.7 16.0 40.7
    Dairy 18.8 9.0 29.5
    Llama 5.5 4.1 6.9
    Hog 34.8 a --
    Dairy Compost 24.5 12.8 43.6
    Turkey Compost 35.8 2.4 42.2

    a only one sample was tested

    Areas with well-drained soil and copious amounts of precipitation may not suffer from the addition of high salt manures. These conditions may permit the leaching (washing) of salts below the plant's roots. However, high salt manures added to heavy (clay-based) soils in areas with low levels of rainfall may result in a salt buildup in excess of the tolerance level of the plant being grown. This is even more serious for soils already high in salts.

    In lieu of using manure as a soil amendment for soils already high in salt, composted wood chips, bark mulch, chopped straw and other low salt organic matter is recommended.

    The Texture of Manure
    The addition of organic matter to salty soil is a common recommendation. When added to soil, organic matter often improves drainage allowing salts to be leached (washed) below the root system of the crop. This requires the use of an organic matter sufficiently coarse enough to improve drainage and the incorporation of such material deep into the soil. Any organic amendment added should be thoroughly mixed. Layering of such materials should be avoided.

    When a fine textured material such as cattle manure is used, drainage can be blocked preventing the leaching of salts in the amended soil. The combination of fine consistency and high salt level of cattle manure may create a soil much worse than before the manure was added. Pulverizing soil with a tiller or other implement likewise destroys the tilth of the soil creating a situation in which drainage is inhibited.

    The Leaching of soil salts

    The use of a good quality (low salt level) water is required when leaching salts below the rooting depth of plants. In the Tri River Area of Western Colorado and other areas of the arid south-west, well water may be high in salts. Water taken from waste ditches or spring fed ponds also may be high in salt. This is due to these waters flowing thorough salty native soils. These water sources should be checked for salts prior to being used for irrigation purposes.

    Composted Manure
    Compost produced from manures also may be excessive in salts as shown in the table above. While the addition of wood chips, chopped straw, shredded leaves and other low salt materials help dilute the overall salt level of the compost, when such compost is worked into garden soils or used as mulch, salt injury may result.

    Soils, manures and composts can be tested by most soil testing laboratories to determine the salt level.

    Food Safety - the Sixty Day Rule
    Animal manures and composted animal wastes are reported to harbor microorganisms. Even after composting, manure mixes have been shown to harbor such disease causing organisms. Animal wastes contain "pathogens to which humans are vulnerable, including Salmonella and Cryptosporidium" (Animal Water Pollution in America - 1997). There appears to be a consensus recommending animal manures and manure compost not be used until at least 60 days after being produced.

    This waiting period may be critical when using these materials in vegetable gardens.

    Plants uptake antibiotics from manure
    Scientists at the University of Minnesota have been evaluating the impact of antibiotic feeding in livestock production on the environment. Their study published in the July-August 2007 issue of the 'Journal of Environmental Quality' found food crops accumulate antibiotics when planted in soils where animal manure containing antibiotics has been applied. As the antibiotic level in the manure increased, so did the antibiotic level of the crop.
    See for more information.

    Runoff from Manure
    Runoff from feedlots, horse corrals, dog kennels, chicken houses and other sites where animals are confined should not be allowed to enter field or gardens growing edible crops.

    Manure Tea
    Manure tea is produced by some gardeners to water their crops and provide a dilute nutrient solution at the same time. This tea is made by soaking a cheese-cloth bag of manure, either dried or fresh, in a tub of water for several days until the water is the color of dark tea. The solution is then diluted to the color of ice tea and used as a starter solution for transplants or for watering flowers and vegetables.

    The use of manure tea to irrigate crops may also increase the risk of food borne illnesses. The 60 day rule should be complied with when using manures for manure tea. Avoiding feed lot or dairy manure will help reduce antibiotic contamination of food crops.

    Pet Feces
    The question occasionally arises regarding the use of dog and cat feces and litter from cat boxes as soil amendments or as additions to the compost pile. This is not a recommended practice due to pathogens which can affect humans.



    Animal Waste Pollution in America: An emerging national problem - Environmental Risks of Livestock & Poultry Production. December 1997. Report compiled by the minority staff of the United States Senate Committee on Agriculture, Nutrition & Forestry.

    Annonymous. Plants Uptake Antibiotics: Routine feeding of antibiotics to livestock may be contaminating the environment. See

    Davis, J. April 1997. `Hold the salt! Does manure make your ground salty?' in: Agronomy News, Vol. 17, No. 4, Colorado State University Extension.

    Follett, R.H., Westfall, D.G., and Croissant, R.L. 1992. Utilization of Animal Manure as Fertilizer, Bulletin 552A, Colorado State University Extension

    Mayberry, K.S. January, 1998. `Keys to improving food safety in the field' in: Imperial Agricultural Briefs, Extension, University of California

    Shipp, R.F., Jordan, H.C. , Hinish, W.W. and Beegle, D.B. 1981. Profitable Use of Poultry Manure. Pennsylvania State University Extension, Special Circular 146.


    Placed on the Internet March 6, 1998;
    Last updated: 09/18/2007 05:00:14
    Dr. Curtis E. Swift, Area Extension Agent, Horticulture
    Colorado State Extension
    2775 US Hwy 50, Grand Junction, CO. 81503
    voice: 970-244-1840
    fax: 970-244-1700

    regards nemo
    one years weed is seven years seed

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