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CHAPTER 1

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.

It's Elemental

Besides the nutrients that plants get from air and water (carbon, hydrogen, and oxygen), there are at least 14 essential elements that all plants absolutely need in order to live: nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, boron, chlorine, iron, manganese, zinc, copper, molybdenum, and nickel. In addition to these necessary elements, a handful of others may benefit some or all plants, but they aren't universally required: silicon, sodium, cobalt, and selenium. Most plant scientists now refer to this group as beneficial elements.

The number of elements considered either essential or beneficial has grown in my lifetime and probably will continue to. Other elements have been proposed for one or the other of these lists, including chromium, vanadium, and titanium.

Other Citizens of the Soil

Healthy crops arise from healthy soils, and the soil community depends on much more than just plants. There are many other types of organisms living in the soil that work together to make a healthy, functional soil environment. Bacteria, actinomycetes, fungi, protozoans, nematodes, arthropods, earthworms, and other groups of living things all inhabit the soil and perform jobs that help the whole system work well. These organisms, as well as livestock and people, need nutrients beyond what just the plants require. Some other elements that may be required by microbes, animals, and people include bromine, lithium, strontium, tungsten, cadmium, and even arsenic.

Plants are the foundation of our food, even if we also eat meat, fish, or other animal products. When we apply manure to the land we raise our food or feed on, it supplies a portion of all the nutrients plants need to grow, along with most of what the livestock or people who eat those crops need.

Using Manure

Ideally, fertilizer made from manure can:

1. provide enough soluble, readily available nutrients to get a new crop off to a good start.

2. offer enough slowly available nutrients to keep the crop growing all through the season.

3. not lose many nutrients through leaching or other means.

How well that theory plays out in practice depends on the characteristics of the manure, how it's handled and applied, the weather, soil characteristics, and the needs of the crop.

When farmers apply manure consistently over a long time, it can make very long-lasting changes in the soil's fertility. At the Rothamsted Experimental Station in England, manure was applied to a plot of land every year for 19 years beginning in 1852, and then no more manure was applied. More than 100 years later, soils in the plots that received the manure still provided more nitrogen than soils in the other plots.

While it's usually possible to use manure to supply all the nutrients needed for good crop growth, that's not always the best choice. This is because manure contains nutrients that are usually available in proportions that are different from what the crops need to grow well. If we apply manure at rates high enough to satisfy all the nutrient requirements of the most limiting element, we usually apply a lot more of other nutrients.

In some cases, that doesn't cause any problems, but in others it can. In chapter 3, we'll see some examples of how this works.

Biological Characteristics

Besides its nutrient content, manure by its very nature is a source of fresh organic matter, which is almost always beneficial for soils. The term refers to any material that is or was part of a living organism, including plant stems, leaves, roots, bark, soil animals like insects and earthworms, and microscopic creatures like bacteria, actinomycetes, fungi, and nematodes. It also includes the chemical substances that these organisms produce, such as proteins, sugars, fiber, and oils. All of these things — alive, dead and decomposing, or completely decomposed — constitute organic matter.

Organic Matter and the Soil

Soils are vibrant and complex communities of many different organisms, all of whom have a job to do. Soil ecologists estimate that there can be more living organisms in one gram (about a teaspoon) of healthy soil than there are people on Earth — and that's more than seven billion! Fresh organic matter (such as manure) serves as the food source for all these living things except plants (which produce organic matter from the elements in the air, water, and soil). As soil organisms consume fresh or decomposing organic matter, they release many of the nutrients in the organic matter and turn it into forms that can be taken up again by plants.

Good Guys and Bad Guys

Not all of the organisms living in the soil are helpful for the crops we want to grow. Also in the mix are organisms that cause fungal, bacterial, and viral diseases; nematodes and insects that feed on crop plants; and other bad guys. In a healthy and well-balanced system, however, the good guys generally win.

Soil Structure

As these organisms decompose organic matter (or live in a mutually beneficial association with living plants), they also enhance the structure (aggregation) of the soil. When a soil is aggregated, the individual particles of sand, silt, and clay group together into structures called aggregates, or "peds." Earthworms are famous for their activity in forming aggregates. Other organisms, particularly the types of beneficial mycorrhizal fungi that colonize the roots of most plants, produce compounds that keep aggregates glued together.

Each of these aggregates acts like a little piggy bank to hold moisture, humus, and nutrients that help plants to grow well. Between these aggregates are small channels or pores that allow air and water to infiltrate the soil and move through it. These pores also allow microbes to move through the soil and help plant roots penetrate the soil easily so they can develop fully. All these things work together to help bring water and nutrients to the plants so they can thrive.

Humus

The residues produced by these organisms and the remaining organic matter that can't be used as food by anything else that lives in the soil become the substance we refer to as humus. Humus can hold onto and exchange nutrients and water that plants need. It also helps hold soil aggregates together, and it's the substance that gives topsoils their dark color. Humus can take many years to form, and only a tiny fraction of the original organic matter that enters the soil becomes humus. The rest is digested (oxidized) into water and carbon dioxide or becomes nutrients that are used by plants and other organisms in the soil. Thus it takes a huge amount of fresh organic matter to make the tiny amount of true humus in most soils.

All forms of organic matter, from the recently dead organism to the most stable humus, are very important to healthy and productive soils. Manure is one excellent source of this valuable organic matter.

Problems with Manure

While manure is generally great for amending soil, it can also introduce some problems.

Too Much Carbon or Not Enough

When too much carbon-rich bedding like sawdust, wood shavings, or straw is mixed in with the manure, it can cause an imbalance in the carbon-to-nitrogen (C:N) ratio (see below). Most plants, except for legumes whose rhyzobial bacterial friends take care of their nitrogen needs (see box on Nitrogen Fixation), will grow very poorly in these situations. If you find that plants look pale or yellow after you apply manure to their bed, most likely there is too much carbon-rich bedding for the amount of nitrogen in the manure.

Carbon-to-Nitrogen Ratio

The soil organisms that break down organic matter want a diet with a balance between carbon (C) and nitrogen (N). Soil bacteria use the carbon for their energy source and the nitrogen for the protein in their tissues. When the C:N ratio is in the range of 20 — 30:1, decomposition proceeds quickly and efficiently. If the ratio is higher on the carbon side, the soil bacteria will steal nitrogen that plants would otherwise use for their growth. Bacteria always outcompete plants for nitrogen. They won't release it again until they're finished with their meal — days, weeks, or even months later, depending on the characteristics of the residue they are eating. At that point, the nitrogen they have scavenged can be released again and plants can grow normally.

Many types of manure have a lot of nitrogen compared to the amount of carbon if no bedding is added. You can still use this type of material, but it behaves more like a fertilizer than manure with bedding, which we usually think of as a soil amendment. If you apply manure this way, it's important to consider the nutrient content, especially for nitrogen, and not apply it at rates that are higher than the demand for the crop. Applying more nitrogen than what the crop needs can lead to weak plant stems, failure to fruit, or poor-quality vegetables.

Remedies. If there is more nitrogen in the manure than what you want to apply at the rate you want to spread, add more bedding to bring the nutrient concentration down. If there isn't enough nitrogen to balance out the carbon in the bedding, add more bedding-free manure to bring the carbon-to-nitrogen ration into a better balance.

You can also compost the manure or let it decompose naturally in a pile before you apply it. This usually works better with high-carbon manure and bedding mixes than with high-nitrogen materials. With an excess of carbon, the main problem for composting is that it may take a long time. When there is too much nitrogen, the pile can easily become anaerobic, smelly, and runny.

When most of the decomposition is done, the bacterial process is nearly complete and the manure can be applied without any ill effect from inadequate nitrogen.

(Continues…)

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Excerpted from "Managing Manure"
by .
Copyright © 2015 Mark Kopecky.
Excerpted by permission of Storey Publishing.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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