Manure can be a valuable fertilizer for vegetable gardens and has been used for centuries to supply needed nutrients for a variety of crops. Manure not only supplies many nutrients for crop vegetable production but is also a valuable source of organic matter. Increasing soil organic matter improves soil structure or tilth, increases the water-holding capacity soils, improves drainage in fine-textured clay soils, provides a source of slow release nutrients, reduces wind and water erosion, and promotes growth of earthworms and other beneficial soil organisms.
Proper use of manure is essential from both a production and environmental standpoint. Fresh manure is high in soluble forms of N, which can lead to salt build-up and leaching losses if over applied. Fresh manure can also contain viable weed seeds that can lead to weed problems. In addition, various pathogens may be present in fresh manure and can cause illness to individuals eating fresh produce unless proper precautions are taken.
Some states have rules regarding the application of manure to crops grown for human consumption so always check state and local regulations. In the absence of any regulations, a generally guideline is to following the USDA National Organic Program (NOP) Standards Final Rule, which states that if raw manure is applied to crops for human consumption, it must be incorporated 120 days prior to harvest of a crop that comes in contact with the soil (i.e. root crops or leafy crops that grow low to the ground). If the product does not have direct contact with the soil (tomatoes, beans etc.) the manure should be applied at 90 days prior to harvest.
Manure can be composted prior to use on vegetable to reduce the risk of pathogens as well as kill most weed seeds. The heat generated during the composting process will kill most weed seeds and pathogens, provided temperatures are maintained at or above 131°F for 15 days or more (and the compost is turned so that all material is exposed to this temperature for a minimum of 3 days).
For more information:
USDA National Organic Program Rules
Manure and Compost Use on Fruit and Vegetables
Author: Mark Rice, North Carolina State University
