Gardeners love to talk about their gardens. The range of topics is never-ending—the best bean for canning, the most flavorful tomato, how to manage the array of pests that challenge a relaxing morning in the garden and best practices for enhancing soil texture, structure, and fertility. Applying manure to a vegetable garden impacts all facets of soil health: texture, structure, and fertility.
Soil texture is the term used to describe the percentage of sand, silt, and clay in the soil.From a particulate perspective, sand is the largest particle, and clay is the smallest.The soil triangle provides a graphic representation of the combinations.While the texture cannot be changed, adding organic material such as manure will alter soil structure.From an agronomist perspective, soil structure refers to how soil components aggregate to form air and water spaces within the soil.Air and water are critical for good root, and therefore plant, development.
Two often used examples of how manure impacts soil are: for texture, adding manure (organic matter) to a sandy soil will increase the soil's ability to absorb and retain moisture. Adding manure to a clay-based soil will increase the soil drainage by creating those same spaces. When considering soil amendments, remember adding organic matter (manure) cannot change the soil texture as the percentages of sand, silt, and clay remain the same; however, the soil structure can be altered by adding manure to the soil. While this article refers primarily to using manure in a garden where edibles grow, the texture and structure properties are the same in any type of garden where soil is present.
Applying manure is not a new technique for growing crops. Although manure is commonly thought to make soil more productive, it is not technically fertilizer. Research conducted by Amy Bogaard, an archaeobotanist at the University of Oxford, reported in this article Fertilizer History P1, published by the Institute of Agriculture and Natural Resources that the benefits of manure to plant growth were observed almost 8,000 years ago! If you enjoy an interesting science read, have a look at the article. The dating description process provides an interesting insight into projects where an archaeobotanist is a key investigator/researcher.
What are the effects of adding manure to a home garden? Remember, manure is not a fertilizer.There is no guaranteed analysis with manure, as there is with packaged fertilizer. For instance, 10-10-10 fertilizer is guaranteed to provide equal amounts of nitrogen, phosphorus, and potassium. This is important to know because nutrient requirements differ by plant type (for example tomato vs. cucumber) and within a plant depending upon the stage of growth. As an example, a tomato setting fruit requires less nitrogen, because vegetative growth should yield to fruit set and phosphorus and potassium are directly involved in fruit set.If you would like an analysis of the manure you are adding to your garden soil, Penn State University Soil Analysis Lab does offer manure testing. Please see this link for information regarding the test and analysis: Agricultural Analytical Services Lab Manure Testing.
Today, gardeners can obtain a variety of manures from local farmers and lawn and garden stores.Some grocery stores even offer bagged manure. In addition to numerous commercial and private outlets for getting manure, there is also a broad choice of types of manure. Manure from farm animals such as cows, horses, sheep, goats, llamas, and chickens is commonly used in vegetable gardens. Local farmers may be more than willing to offer manure free of charge because it reduces the amount of manure the farmer must safely manage. Horse and cow manure often are loaded with weed seeds that can be neutralized by composting at a temperature of 140℉. Goat and sheep manures have the advantage of being naturally pelletized. Pelletized manure is easier to handle and often easier to spread in a home garden but should be used in accordance with the guidelines included in the following paragraphs.
According to several references, pig manure should not be used in a garden where edibles are grown.The same is true for dog, cat, and human waste due to the possible presence of parasites.
Many gardeners have ready access to chicken manure.Chicken manure is often referred to as "hot" due to high nitrogen content.Coop bedding added to the chicken guano may dilute the concentration of nitrogen in the manure. High nitrogen content may burn tender seedlings, so it should be composted prior to use in a home garden
Over the years, news stories have documented people becoming ill and, in some cases dying, as a result of eating produce infected by parasites and/or bacteria. Most notably are the incidents involving E. coli, Salmonella, and Listeria contaminated vegetables. According to the University of New Hampshire article entitled Guidelines for Using Animal Manures and Manure-Based Composts in the Garden (PDF)“To ensure that pathogens have been killed, the compost pile must reach a high temperature (between 113℉ and 140℉) for a sustained period of time (several weeks)."The article further states, “The compost must also be turned regularly and carefully monitored so that all the manure has been exposed to sufficient temperature.In home compost piles and in unmanaged manure piles, this rarely happens.Aged manure is not the same as composted manure, and is not safe to assume that pathogens in an aged manure pile have been destroyed. However, if the pile has reached an internal temperature of 140℉, weed seeds will be no longer be viable."
According to the paper written by Steven Ingham, University of Wisconsin-Madison, Safely Using Manure in the Garden, the issue of manure contamination of edibles was addressed by the USDA National Organic Program. While the guidelines set forth by theUSDA National Organic Program are for certified organic vegetable growers, these guidelines are viewed as best practices and followed by non-certified organic growers as well. The guidelines explained below, are simple, straightforward, and can be observed by home gardeners without issue.
In an effort to reduce health risks when using manure in home gardens, the USDA National Organic Program suggests waiting 120 days from application to harvest for edibles that grow in or touch the soil. For other crops, the recommended wait time is 90 days from application to harvest for these edibles.
Summary Points
Adding manure to the home vegetable garden can increase soil organic matter and may alter soil structure. Adding manure to soil will not change soil texture. Fall is the most common time of year for adding manure to a vegetable garden. The manure may be spread atop the soil or incorporated into the garden soil.
Pig, dog, cat, and human waste should never be used in a vegetable garden. Cow, horse, chicken/poultry, sheep, goat, and llama manure are acceptable types of manure appropriate for use in vegetable gardens.
There are differences in using raw, aged, and composted manure in a garden. Manure may be composted in a variety of means, for the home gardener, this is usually hot or cold composting. Large amounts of agricultural manure is sometimes composted in windrows. The method of composting is a personal one and the literature is flush with options.
The USDA National Organic Program has created guidelines for certified, organic growers. These guidelines may also be integrated into manure management and composting programs used by home gardeners.
Llama manure.Photo credit: Diane Diffenderfer.
References
Agricultural Analytical Services Lab Manure Testing
Bulletin #2510, Guidelines for Using Manure on Vegetable Gardens, The University of Maine
Fertilizer History P1, University of Nebraska – Lincoln, Institute of Agriculture and Natural Resources CROPWATCH
Guidelines for Using Animal Manures and Manure-Based Composts in the Garden (PDF), University of New Hampshire
How to Fertilize a Garden (PDF), Texas A&M Agrilife Extension Easy Gardening
Introduction to Organic Practices(PDF), USDA
Safely Using Manure in the Garden, University of Wisconsin Extension
Tipsheet: Manure in Organic Production Systems (PDF), ATTRA Sustainable Agriculture
Using Manure in the Home Garden, Wisconsin Master Gardener
Vegetable Gardening, Penn State Extension
