|By Jay White
For about as long as people have been growing plants for food or ornamentation, they have known that dried animal feces mixed in their soil produced healthier plants and more abundant harvests. Throughout the ages, humans have nurtured their soils and their plants with every type of manure imaginable. In less-developed parts of the world, manures still provide the bulk of nutrients for the third-world’s harvests. As gross as this may sound, human poo, or humanure as it is called in the organic-fertilization world, fertilizes many, many rice paddies across the globe. Permaculture is a closed-looped, organic system that uses fish-poop-infused water to feed plants which in turn filter the poop out of the water to use as fertilizer and then return the clean water back to the fish tank. Yes, if there is poop out there, humans have figured out how to use it in the garden.
Before the 1950s in America, animal manure was the backbone of commercial agriculture. However, after World War II, commercially made chemical fertilizers became cheap and readily available. While many farms today still spread composted chicken litter or a water/chicken manure slurry on their fields, the use of manures has been mostly relegated to organic gardens and small-scale organic farms. While people understand that manure is good fertilizer, it is not universally understood why it is or how it works.
What is Manure?
Manure is organic matter that is derived from animal feces or is, in the case of green manure, a crop grown specifically to be tilled back into the soil. Both of these can be used as fertilizer in organic agriculture. So, manure is not just animal poop! Manure is what is left behind after natural decomposition processes stabilize animal and plant waste. These stabilized organic materials that we call manure are the chief inputs of the composting process.
While it might surprise you to learn that manure can come from both plants and animals, it is important to be clear about what manure is not. Manure is not feces! Manure is the solid parts of feces or dead plants that are left behind after time, temperature and microbes have done their work on them. While manure is a dry, (mostly) odorless, safe product that is easy to work with, feces is “wet,” stinky animal excreta that can harbor deadly bacteria and viruses. Human feces can carry cholera, dysentery and salmonella. Chicken manure can also carry salmonella and a deadly respiratory fungus called histoplasmosis. Every outbreak of E.coli that has made the news in last few years has been caused by cattle diarrhea that contaminates water sources used to water vegetables. Because of this, gardeners should never use raw feces in their gardens (with one exception we will cover later).
Before we can understand how manures feed our plants, we need to review how fertilization works. Fertilization is the process of providing essential nutrients to plants. While most discussions of fertilization focus on nitrogen (N), phosphorus (P) and potassium (K), it is important to note that plants require 17 separate nutrients to thrive. Plants get hydrogen, oxygen and carbon from the air or the soil. The other 14 nutrients are divided into three categories. Macronutrients (nitrogen, phosphorus and potassium) are the three elements plants need most and why you see them listed on every bag of fertilizer. Secondary nutrients (calcium, magnesium and sulphur) are required nutrients needed in smaller quantities. Finally, trace minerals (boron, copper, chlorine, iron, manganese, molybdenum nickel, and zinc) are also required by plant processes but in very low amounts.
Whether you feed your plants from a bag of fertilizer or a pile of manure, the same precautions apply. Before doing any fertilization, get a soil test. Plants can only use so much of each of the 17 elements. If they don’t get enough, they suffer and if they get too many, they suffer. All types of fertilizers supply these nutrients in varying amounts. A soil test will give you the information you need to create and implement a balanced feeding plan for your plants.
Certain herbicides can pass through the digestive system of farm animals. If this happens, then despite your best organic efforts, your plants will suffer herbicide burn. Because of this outcome, it is important for you to know the source of your manure. Unlike coastal Bermuda grass, alfalfa is not sprayed for weeds; so there is a lower chance that your compost will have herbicide contamination if it comes from a dairy.
Organic vs. Chemical
I am an organic gardener, but I am also a scientist (or at least I played one in graduate school). Most people I know who have chosen to grow organically do it out of a sincere concern to grow food that does not harm the earth or the people on it. Organic growers believe that synthetic pesticides, herbicides and fertilizers damage our soil, water and air; and the food grown with them can damage our bodies. While I agree with organic growers on most points, I am not anti-commercial fertilizer. Much research has been done and it overwhelming supports the conclusion that plants cannot tell where their nutrients come from.
A good example is nitrogen. Plants need lots of nitrogen. However, they can only use it when it is in one of its two ionic forms — ammonium (NH4+) or nitrate (NO3-). If the nitrogen in the soil is not in one of these forms, it is not available for the plant to use. Whether you use composted manures or a bag of ammonium nitrate (34-0-0) to supply these essential ions, the plant cannot tell the difference. If plants cannot tell where their nutrients come from, why would you chose one fertilization method over the other?
If you are producing crops for market, the use of commercial fertilizers makes sense. They work great, they are inexpensive and they may allow you to get higher yields or one more crop a year out of your soil. However, if you are not a commercial grower, my experience has shown that you just don’t need commercial products to grow a great garden. You can grow lots of healthy plants, that provide large yields, with organics — and you can do it at a lower cost than commercial products. I really like the fact that it is almost impossible to overuse organic fertilizers. If you do accidently over-apply organics in your garden, it is very unlikely that they will damage anyone else’s water, property or crops that are downstream from yours.
Another thing I love about organics is that they are nature’s original “slow-release” fertilizers. Composted manures do not act quickly. The nutrients in manure’s organic solids are in stable forms that are much more resistant to leaching. In fact, the nutrients in manure’s organic solids are not even available until they have been released by the micro-organisms, invertebrates and insects in the soil. These organisms consume the organic compounds in the manure and then their metabolic processes convert the organic solids into plant-useable forms of nutrients. An organic-fertilization program that relies on manures should be thought of as a continual soil-improvement program that will slowly and steadily provide (almost) all of the macro-, secondary and micronutrients required for healthy plants.
While commercial fertilizers are great at rapidly providing available nutrients, they too often focus on the macronutrients. While there are balanced commercial fertilizers available, many types lack secondary and trace minerals. This is one area where organics excel. Manures, and especially manures that are composted with other organic materials such as hay or mushroom waste, generally supply most, if not all of the 17 nutrients required to support plant life.
In my opinion, the chief drawback to using commercially produced fertilizers is what happens when they are overused. Whether they are purposely put out at too high a rate or they are overdone because of broken or poorly calibrated equipment, it is very easy to apply too much fertilizer. When there is too much fertilizer in or on the soil, rains carry it downstream. High levels of nitrogen in streams and rivers are blamed for algae and moss blooms that can suck all of the oxygen out of a tank, river or lake, killing fish and other vertebrates.
While commercial fertilizers give you the ability to quickly put out too much nitrogen, organics make it almost impossible to do so. Have you ever heard someone say, “That compost is so hot it burned my plants”? I have heard that statement many times in my gardening career. Let me assure, it is not true. Plants get “burned” by fertilizer when there is too much nitrogen in it. Dry manures simply do not contain enough nitrogen to burn plants. The nitrogen in animal manures ranges from half a percent in cow manure to 2.4 percent in rabbit manure. If there is a problem with organics, this is it. It is often hard to get enough nitrogen to your plants when using only manures.
While these low-nitrogen levels can be a problem for feeding growing crops in the garden, it is great for feeding plants in pots. Ninety percent of nitrogen in animal manure is tied up in a form that must be converted to ammonium (NH4 –N) before it can benefit the plant. However, that means that around 10 percent of the total nitrogen in feedlot manure is already in the usable form of ammonium. You can take good advantage of this “free nitrogen” to create a well-balanced fertilizer that you can use at will on your potted plants. I make my “teas” by steeping dried manures (or composted manures) in water. After the manure has steeped for 24 to 48 hours, I strain off the solids and put the resulting suspension in a small pump-up sprayer. I use this on my plants weekly, and sometimes twice weekly in the summer. In addition to feeding the plant, manure teas have been shown to have some disease- and pest-fighting benefits.
While I am a fan of “teas,” there is some controversy around the use of them. The amount of nutrients contained in the teas is so low that many in the scientific community question their effectiveness. While I cannot prove scientifically that the compost teas I make benefit my plants, I truly believe they do. I regularly use teas on my potted plants. Their nutrient level is so low I can water my potted plants two or three times a week and not worry about “burning” them or causing any other toxicity problems.
Types of Manure
Not all manures are created equally. Manures made from barnyard animals vary greatly in the amounts of nutrients they contain. After receiving the results of your soil test, you can use Chart 1 to help create the manure blend that will best compensate for the deficiencies in your soil.
Cow Manure. In its raw form, all manures have much higher nutrient levels than they do in their composted or dried forms. Wet cow manure is about 3 percent N, 2 percent P and 1 percent K. Unfortunately, the nitrogen in the fresh manure is ammonium and that much nitrogen will definitely burn your plants. Composted cow manure makes up the bulk of my soil-feeding routine. Where I live, I can buy bulk compost that is made of a blend of dairy manures and mushroom waste. This compost has most of the nutrients my plants need. In addition, the large amounts of organic solids in the mix make my black clay soils drain better. Conversely, these compost/manure blends will also help sandy soils retain moisture.
Horse Manure. Horse manure is similar to cow manure in its make-up and benefits. However, because horses only have one stomach, more weed seeds pass through their digestive track. For this reason, you need to make sure that your composted horse manure reached 140 degrees during the composting process. I cannot verify this scientifically, but an old gardener I know swears that if you make a tea out of horse manure and apply it to your potatoes, you will never have a single potato bug.
Chicken Manure. When I was a young man, I worked on a chicken farm. One of my jobs was to fill the “honey wagon” with a liquid chicken manure slurry and then spray it on the wheat. One day, the coupling on the line that sucked the manure into the tank gave way and I quickly found myself covered in liquid chicken manure from head to toe! Guess what happened? The skin all over my body received a light burn from all of the nitrogen in the slurry. Ever since that day, I have had a ton of respect for chicken manure. There are lots of chicken farms in Texas, so there is a lot of chicken manure available to gardeners and farmers alike. Chicken manure has the second-highest concentration of nitrogen of all of the barnyard manures, so I definitely encourage you to use it. Just be careful if you make it yourself.
Sheep Manure. If your soil test shows you are low in potassium, find yourself some sheep manure. Besides having the highest concentration of potash of all the manures, sheep manure is high in organic matter. So it conditions the soil much like cow manure. Also, since sheep are ruminants, their manure will contain very few viable weed seeds.
Rabbit Manure. One of the healthiest gardens I have ever seen was in the backyard of Elm Mott gardener Dorothy Gremela. She and her husband raise rabbits for food. They use their rabbits’ poop and bedding straw to feed their garden. Their plants were so beautiful and healthy I immediately went out and found myself a source of rabbit manure.
If you search the internet, you will find many people talking about how high in nitrogen rabbit manure is. While this is true, you have to read carefully. Fresh rabbit manure is super high in nutrients. Dried or composted rabbit manure has about the same amount of nutrients as dried sheep manure.
Remember how I said earlier that you should never use feces in your garden? Well, rabbit manure is the exception. As far as I have been able to determine, there is about a zero percent chance that rabbits will pass any diseases to humans through the use of their feces in the garden. If you can find a source of fresh rabbit poo, I highly recommend using it. In fact, it is such good fertilizer that I have often thought about raising a few rabbits myself. One doe and her resulting offspring can produce a ton of “bunny honey” per year.
Urine. While urine is not technically a manure, it is a very useful organic fertilizer. Raw urine has an approximate nutrient content of 11-1-2.5. This is very similar to many commercial fertilizers. I know the thought of gathering and using your urine to “water” your plants is a little too “out there” for most folks. However, your plants will definitely thank you, if you can stomach it. This is why chicken manure is so high in nitrogen. Chickens expel both liquid and solid waste out of the same orifice. It is the “urine” in their poop that makes the chicken manure so high in nitrogen.
I did not choose to become an organic grower because I feel commercial fertilizers are bad things. In fact, I truly believe that the preponderance of evidence shows that plants (and the fruits they produce) cannot tell if their nutrients came from a bag of fertilize or the back end of a cow. I am an organic grower today because I learned to grow vegetables from a man who knew that you did not have to buy synthetic fertilizer to grow a healthy and bountiful garden. He knew that gardening was much more than just a harvest. Gardening is a lifestyle that makes you aware that everything God has created is beautiful and has a purpose — even if it’s poop!