Characteristics of Manure

The Nature and Properties of Crap

The physical, chemical, and biological properties of manure make it a truly amazing soil amendment. Depending on the species of animal, the type of bedding used, and how manure is stored and spread, some type of manure is an appropriate soil amendment for almost every crop grown in almost any type of soil, anywhere in the world.

To make the best use of manure, it helps to understand its properties, along with the requirements of the crops you're growing and the characteristics of your own soils.

Physical Properties

Fresh manure is usually moist, its consistency ranging from firm and well formed to almost a slurry. Depending on the animal it comes from and what that animal eats, it may have a mild, earthy odor or a strong and unappealing smell as it is excreted.

How manure is collected and stored and whether or not bedding is included affect its physical characteristics as well as its nutrient value. Manure that has been composted doesn't even resemble the original material, being well mixed, mellow, and pleasant to the smell. Manure that is stored as a liquid in a lagoon or holding tank doesn't resemble the original material, either, but usually has a powerful odor and requires special equipment to deal with it.

Because small-scale farmers and gardeners most often will be working with solid manure, that's what most of this book will focus on.

Manure Production

It's handy to know how much manure you can expect to get from whatever kind of livestock you keep. If you consider the weight of the animal, there's a fairly narrow range of how much dry matter (the weight of the material without any water) different livestock species excrete in their manure. For each pound of live animal weight, cattle produce the least — around 3 ¾ pounds (1.5 kg) per year; horses, sheep, and swine around 4 pounds per year; and poultry around 4 ¼ pounds (1.9 kg) per year.

If you consider the actual fresh weight of the manure (including moisture), however, the range is much wider: poultry, sheep, and horses produce between 11 and 12 pounds (5–5.4 kg) of actual fresh manure per pound of live weight each year, while cattle produce 26 to 38 pounds (11.8–17.2 kg) and swine around 25 to 26 pounds (11.3–11.8 kg) per year for each pound of live weight. There's quite a range in the moisture content of manure excreted by the various species (see chart). In addition, some types of livestock manure almost always come with some bedding for good measure.

The physical (and chemical) characteristics of manure vary by species, bedding types, and storage and handling systems. The species of livestock the manure comes from is the starting point and has the most influence, so it's helpful to understand the differences.

Manure Production Stats

Here are some of the ranges in moisture and overall annual production for fresh manure (not including bedding) from several types of livestock. Note: the weight of bedding can be substantial.

Cattle dung can be either cakey (when cattle are fed low-quality hay or graze overmature pastures) or very runny (in high-producing dairy cattle or any livestock grazing on lush pastures or other extremely high-quality forages).

Small ruminants (sheep, goats, and rabbits) usually have nicely formed, relatively dry, pelletized feces.

Horses tend to make bigger "balls" of manure (sometimes called horse apples).

Swine have stools that are poorly formed and quite wet.

Poultry manure is a bit drier, but it's very concentrated and is a mixture of both solid and liquid waste, since birds don't urinate.

Chemical Characteristics

Aside from the nutrients that leave the animal (or the farm) in the form of meat, milk, or fiber, almost everything livestock eat gets passed along in their feces and urine. On average, an animal excretes around 70 to 80 percent of the nitrogen, 60 to 85 percent of the phosphorus, and 80 to 90 percent of the potassium in the feed it eats. Since most of these animals' diet comes from plants, this is a great opportunity to recycle the nutrients needed for producing more crops. And this recycling isn't limited only to the major plant nutrients of nitrogen, phosphorus, and potassium; it also includes minor and micronutrients essential for plant growth.

Number One or Number Two?

The solid part of manure (dung or feces) differs greatly from the liquid portion (urine) in its chemical properties. In order for plants to use them, nutrients must be in a soluble form. Manure holds both soluble (available) and decomposable (slow-release) plant nutrients.

Not all the feed an animal eats is completely digested as it passes through the animal. Because the undigested solids that pass through an animal are contained in the feces, it stands to reason that it will take longer for any nutrients in them to decompose in the soil before the plant nutrients they contain can become useful to crops. Urine, on the other hand, only contains substances that are completely dissolved, so most of the nutrients in this liquid are available almost immediately for plants to use. This combination of quickly available and slowly available plant nutrients gives manure the ability to provide both short-term and slow-release plant nutrients.

The proportions of urine and feces in excrement, and their chemical characteristics, also vary by species. Poultry excrete everything as feces. Cattle and horses excrete around 80 percent of their output as feces; for sheep it's about 67 percent; and for swine, about 60 percent.

Chemically, the proportions of the "big three" plant nutrients also vary by species. Here's what it looks like on average for four species.

The proportions of solids and liquids and their respective nutrient contents are important, because the system you use to collect the manure can influence the nutrients in the stored product. If the collection and storage system you have catches and stores the urine, you'll have a better product than if the urine is lost.

For example, if a farmer scrapes up cattle dung from a holding area or feeding pad, the resulting manure will have much less potassium than in a contained system (stall barn, freestall barn, bedded pack, compost barn, etc.) that catches both the urine and the dung, because most of the potassium that cows excrete is in the urine.

Manure as a Fertilizer

Manure is an excellent source of plant nutrients, because most of what animals eat comes from plants, and most of what the animals eat gets passed through in the excrement. All plants require a certain number of elements for their growth, and some plants benefit from a few others.

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