Extension Educator, Horticulture
Supply and demand. Only livestock producers and gardeners spend much time thinking about manure. Producers have it and gardeners want it. But is it as simple as dumping a pile of manure on your garden?
First some terminology. Compost and manure are not the same even though I often hear newbie composters using the terms interchangeably. Composting is the controlled decomposition of organic materials (stuff that use to be alive) using aerobic bacteria (ones that need oxygen, not the smelly anaerobic kind) and fungi, but also protozoans, millipedes, beetles, and worms. Manure is…well you know….manure, but will often include whatever bedding the producer is using such as sawdust or straw.
All compost is not created equal. It depends on the initial ingredients and the composting process. Neither is all manure created equal. For example poultry manure has a much higher nutrient content than horse manure.
So which is better? Compost or manure? It all depends. Both will improve soil structure for healthy plants. Manure can be appropriately applied to farm fields. It has higher nutrient content than compost and is readily available in large quantities. Manure could be applied to a fallow garden now so it has time to compost in place before spring planting. For gardeners a safer route is to compost manure before applying it to gardens for a number of reasons.
Composted manure is easier to spread, less likely to contain weed seeds and usually has fewer odors than fresh manure (although poor composting can cause odors).
Food safety is a major concern in using uncomposted manure. According to the Pacific Northwest Extension publication "Fertilizing with Manure" fresh manure can sometimes contain pathogens that can cause diseases in humans. Salmonella bacteria are among the most serious pathogens found in animal manure. Pathogenic strains of E. coli bacteria can be present in cattle manure. Manure from swine and carnivores can contain helminths, which are parasitic worms. These pathogens are not taken up into plant tissue, but they can adhere to soil on plant roots, or on the leaves or fruit of low-growing crops. Or on poorly washed hands.
Cooking destroys pathogens, but raw food carries a risk of pathogen exposure. Washing and peeling raw produce removes most pathogens, but some may remain. The risk from pathogens is greatest for root crops (e.g., carrots and radishes) or leaf crops (e.g., lettuce or spinach), where the edible part touches the soil. The risk is negligible for crops such as sweet corn, which does not come in contact with the soil, or for any crop that is cooked thoroughly.
Consider any raw manure to be a potential source of pathogens, and avoid using fresh manure around high-risk crops. Bacterial pathogens die off naturally during extended storage or after garden application. Complete die-off of bacterial pathogens occurs in days to months depending on the pathogen and environmental conditions. Helminths in swine manure can persist in soil for years, however.
Composting manure at high temperatures will kill pathogens, including helminths, but careful quality control is needed to ensure that all of the manure reaches a high temperature for pathogen kill.
Fall is a great time to start a compost pile. Compost can be made from a wide variety of sources including manure, autumn leaves, vegetable food scraps and the remnants of garden plants. Finished compost is "black gold". As a great soil conditioner it loosens heavy clay soils, improves water-holding capacity, adds all the wonderful microbes and fungi back into the soil and adds important plant nutrients. Compost feeds the soil that feeds your plants.
University of Illinois Extension website Composting Central contains a multitude of information about composting for home gardeners, livestock producers and farmers including Manure Share. No it's not the latest political attack ads. Manure Share connects producers and gardeners/landscapers that have manure or want manure.