MN Fruit & Vegetable IPM News - Vol. 4, No. 3

Manure has been used as a soil amendment for centuries by farmers to improve plant growth. Manure not only supplies many nutrients needed by plants, including micronutrients, but it is also a valuable source of organic matter. Increasing soil organic matter improves soil structure or tilth, increases the water-holding capacity of coarse-textured sandy soils, improves drainage in fine-textured clay soils, provides a source of slow release nutrients, reduces wind and water erosion, and promotes the growth of beneficial soil organisms. Although there are many benefits of using manure for crop production, proper management is essential to prevent potential illness to humans, environmental contamination, and poor plant growth. The purpose of this article is to provide guidelines for effective and safe use of manure for vegetable crops.

All types of fresh manure pose some health risk to humans if not properly handled or processed. Fresh manure from all animals contains various strains of bacteria such as Eschericia coli (E. coli) that can cause gastro-intestinal illness with symptoms ranging from an upset stomach and diarrhea to death in people with weak immune systems. The recent problems associated with fresh spinach and lettuce consumption were related to contamination with manure at some stage during production, processing or handling of the produce. Even though the contamination does not always occur during the production stage, the outbreaks have made people more aware of the potential problems related to manure use.


Composting manure in wind rows

For most situations involving vegetable crops, manure should be composted or heat treated before use. This is especially important if the manure is being used as the nutrient source to grow vegetables or fruit for fresh consumption or if it is being used as a mulch. Heat generated during the composting process will kill most pathogens, provided temperatures are maintained at or above 131°F for 15 days or more (and the compost is turned several times so that all material is exposed to this temperature for a minimum of 3 days). The heat generated during composting will also kill most weed seeds, which is an added benefit. When handling fresh manure for composting gloves should be used and hands washed before eating food.

Do not harvest produce into containers that have been used to transport manure and thoroughly wash tools, gloves and other items used to handle manure before using them in crop production areas. Aged manure, or manure that has sat for an extended period of time and is partially decomposed, will have lower pathogen levels than fresh manure; however, it may not be pathogen free and it is safest to treat aged manure in the same way as fresh manure is treated.

Dried manure products are also available. Drying manure or compost to a low moisture content reduces their volume and weight. Dried products can be easier to handle and apply more uniformly to fields, especially those products that have been processed into pellets. Heat drying will eliminate most pathogens if temperatures exceed 150 to 175°F for at least one hour and water content is reduced to 10 to 12% or less. One advantage of dried manure is that it will have a much higher nutrient value than composted manure.

Organic standards currently allow the use of fresh manure if it is incorporated into the soil at least three months before an above ground edible portion of a crop is harvested or four months crops where the edible portion is in direct contact with the soil. For many crops and under Minnesota’s climatic conditions, this often means that fall application and incorporation after the current season’s crops are harvested is necessary. Given the higher risk of contamination with leafy vegetables like spinach and lettuce, it is safest not to grow these crops following fresh manure application at any time. Do not surface apply fresh or partially composted manure under plants or trees where fallen fruit will be eaten or where children will be playing.

Many different types of manure composts and dried manure products are available. The nutrient content of these products varies with animal, bedding, storage, and processing. In most situations, manure and compost application is based on the available nitrogen content. If soil test phosphorus is excessively high, then application may be based on available P content. Poultry manure compost usually has higher nitrogen content than compost made from horse or cattle manure. Applying rates that are too low can lead to nutrient deficiency and poor plant growth. On the other hand, too high a rate can contribute to nitrate leaching, phosphorus runoff leading to algal growth in lakes, and excessive vegetative growth of some crops. Examples for calculating the rate of manure or composted manure to apply can be found at: http://www.extension.umn.edu/distribution/horticulture/M1192.html

Key Points

Manure is a valuable source of organic matter and nutrients for the soil
Fresh manure can pose human health risks if not properly handled or processed
Manure is most safely used if it is composted or heat treated before being added to the soil, especially when vegetables or fruit for fresh consumption are grown or it is used as a mulch
Heat generated during composting will kill most pathogens if the pile is maintained at or above 131°F for 15 days and all parts of the pile are exposed to this temperature for at least 3 days
When handling fresh manure for composting, gloves should be worn and hands washed before eating food; thoroughly wash tools, containers, and other items before using them in crop production areas
Handle aged manure with the same precautions as fresh manure
Fresh or partially composted manure application is permitted by organic standards if it is incorporated into the soil at least three months before harvesting an edible above ground crop or four months before harvesting a root crop; however, because of higher contamination risk, do not grow leafy vegetables such as spinach or lettuce on ground that has received any fresh manure
Unless soil is excessively high in phosphorus, apply manure or composts at rates based on their available nitrogen content; avoid both over- or under-application

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ACKNOWLEDGEMENTS

Co-Editors: Bill Hutchison (hutch002@umn.edu), Department of Entomology, University of Minnesota, Jeanne Ciborowski, Minnesota Department of Agriculture, Ag. Resources Management and Development Division, and Suzanne Wold-Burkness (woldx018@umn.edu), Department of Entomology, University of Minnesota

The Newsletter is published weekly from May through August, cooperatively, by the Minnesota Department of Agriculture (MDA) and the University of Minnesota (U of MN). Reports are posted on the U of MN and MDA web sites on Fridays. If you have suggestions and/or comments, please send your contributions by 4 p.m., Wednesday to Jeanne Ciborowski, 651-201-6217, jeanne.ciborowski@state.mn.us , MDA, 625 Robert St. North, St. Paul, MN 55155. You can access the Newsletter at the U of MN web site in htm format at: www.vegedge.umn.edu/MNFruit&VegNews/mnindex.htm and at the MDA web site in pdf format at: www.mda.state.mn.us/plants/pestmanagement/ipm/ipmnews.htm

Partial funding for this publication is provided through partnership agreements with the Minnesota Fruit and Vegetable Growers Association (MFVGA) and the United States Department of Agriculture – Risk Management Agency (RMA). These institutions are equal opportunity providers.

DISCLAIMER

Reference to products in this publication is not intended to be an endorsement to the exclusion of others which may have similar uses. Any person using products listed in this publication assumes full responsibility for their use in accordance with current manufacturer directions.

Last Revised May, 2007 by woldx018@umn.edu
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