 One of the things that became clear to me in planning the chicken food forest is that one must think carefully about what happens to the chicken poop, because too much of it can cause the whole food forest to go quickly off the rails (photo: a fresh item of the topic of discussion).  People extoll the benefits of chicken manure as a compost ingredient – lots of nutrients to enrich your vegetable and flower gardens! Yet, when you see a chicken yard, it’s a place where nothing grows – it’s just bare, dead dirt. The photo here shows what chickens were able to do to the three sisters garden area in just four weeks. So I guess chicken poop can be really good or really bad. We don’t want the chicken food forest to become a dead chicken yard; we want it to be rich in vegetables, flowers, trees, and shrubs. It turns out you need to get the chicken poop - nitrogen cycle just right: the right amount of chicken poo leads to an awesome garden; too much chicken poo leads to chicken yard desolation. And just because nothing is simple, the “just right” amount can vary by a lot, depending on what you’re growing, your soil type, how much rain you’re getting, the season of the year, status of the solar eclipse…. (ok, not the eclipse). Chicken manure is obviously complex stuff with lots of different materials in it, but an important one is nitrogen. The nitrogen carries sizeable weight in both the benefits of chicken manure, and in its destructive potential. Nitrogen is a critical nutrient for plant growth, and too little of it leads to stunting, weakness, and eventually death; but too much of it overwhelms plant roots, also leading to death. Realizing this, I saw that I would have to make a detour to understanding the nitrogen cycle as it relates to chickens, their poop, and the chicken food forest. Nitrogen Travels Nitrogen (N) is a basic element, and it cycles around so many forms it makes my head spin. Arghh! Below is the sense that I was able to make of it from a multitude of online sources (listed below). Nitrogen goes from the atmosphere into the soil! Nitrogen makes up 78% of the atmosphere in the form of the element N2 (two nitrogen atoms together). In this form, it can benefit neither plants nor animals. It needs to get into the soil first. It can enter the soil from the air when lightning causes the formation of nitrates (NO3) and transfers those molecules into the ground (kaboom!), but most of it enters the soil when nitrogen-fixing bacteria pull N2 from the air and convert it to NO3. We tend to think of nitrogen-fixing bacteria as those that live in symbiosis with certain plants (peas, beans), but there are also free-living N-fixing bacteria (motto: live free and fix nitrogen!). Nitrogen in the soil gets taken up by plants! Plants can uptake the nitrates (NO3) directly through their roots and when they do, plant life happens. Yippee! In the plants, the nitrates are transformed and used in the formation of important complex organic compounds, like: - chlorophyl, the stuff that makes photosynthesis possible. - proteins, which can be part of the plant’s structural organs or enzymes. - nucleic acids that are part of DNA. - metabolic compounds used for energy transfers. Nitrogen goes from plants into animals! Some plants are eaten by animals, like chickens, and in animals’ bodies, the nitrogen atoms are used to make proteins, components of RNA and DNA, and metabolic compounds – same as in plants! Nitrogen goes from animals into pee and poo! Aha! We have arrived at the chicken manure. Nitrogen is part of every animal’s food – whether in the form of plant or meat or mushroom. Animals will use some of the nitrogen in their food to repair or grow their bodies, but the rest is excreted in urea, feces, or in the case of chickens, combo-packets called chicken poo. Chicken poo contains nitrogen in the form of ammonium NH4 (10-50 percent, average 25 percent) or in the organic compounds in the poo. Nitrogen from pee-poo goes back into plants! If the chicken poo gets into the soil (say by chicken scratching or by rain) the ammonium can become available right away to plants growing nearby. The nitrogen in the organic compounds will need get broken down by decomposers. Some of the decomposers turn the nitrogen within the organic compounds into ammonium (NH4) and some of that NH4 can be taken up by a new plant; but most of it is converted to nitrates (NO3) by other microscopic soil friends, which can also be taken up by a new plant. It’s not entirely clear to me if rain and chicken scratching are enough to get most of the chicken poo into the soil. or do some decomposers come to the soil surface to get it? In any case, I would think that having soil rich in organic soil life would enhance the decomposition rates. Certainly, some farmers spread raw chicken manure on the fields, and it helps with plant growth even if some of it dries up and blows away. Other farmers till the manure into the soil. In our chicken food forest, we would like not to have to rely on hard work like tilling, and my permaculture hero Sean Dembrowsky certainly lets poo lie where it falls, so I think that’s what we will do and see where it leads. Nitrogen in dead plants and animals goes back into the atmosphere or into new plants! When a plant or an animal dies, the same things happen to the bodies as with the organic compounds in poo: they get converted to ammonium or nitrates, some of which get taken up by new plants. But a lot of the nitrates end up being converted some more and released back into the atmosphere as N2. There is a constant loss of nitrogen to the air, so in any given system, it needs to be constantly replenished. Life to life nitrogen cycle! Reading between the lines above, you can see that there is a large N cycle that involves the atmosphere, soil, plants, animals, and back into the air, but there is also a small cycle where the nitrogen just cycles around and around near the earth - in the soil and plant and animal bodies. In the small cycle, nitrogen in the plants is taken up by plants, which are eaten by animals, which produce pee and poo, which is turned back into nitrogen that can be taken up by plants. One could imagine a system where the cycles are turbo-charged – the nitrogen feeding rapid plant growth, which feeds lots of animal life, which creates lots of excreta, which can be used again by the plants; or, lots of soil life cycles the nitrogen back and forth between the air (N2) and the soil (NO3 and ammonium).  Life to life nitrogen cycle! Reading between the lines above, you can see that there is a large N cycle that involves the atmosphere, soil, plants, animals, and back into the air, but there is also a small cycle where the nitrogen just cycles around and around near the earth - in the soil and plant and animal bodies. In the small cycle, nitrogen in the plants is taken up by plants, which are eaten by animals, which produce pee and poo, which is turned back into nitrogen that can be taken up by plants. One could imagine a system where the cycles are turbo-charged – the nitrogen feeding rapid plant growth, which feeds lots of animal life, which creates lots of excreta, which can be used again by the plants; or, lots of soil life cycles the nitrogen back and forth between the air (N2) and the soil (NO3 and ammonium). Here is a simplified drawing of my understanding of the nitrogen cycle as it relates to chickens.  Replenishing nitrogen
As mentioned, nitrogen is constantly being lost back into the air. In many ecosystems, the “nitrogen fixing” plants compensate for that (parentheses because it’s the bacteria that do the fixing; the plants are hosts). In permaculture designs we intentionally include such plants. But with chickens, we usually bring in outside food to supplement what the chickens can get from scratching around, and this input is a human-created inflow of new nitrogen. With a lot of chickens and a lot of human-induced nitrogen inflow, we need to consider that we’re not overloading the system with nitrogen. Too much nitrogen and collapse. We have to watch the nitrogen because when there is too much coming in, it overwhelms the soil life, ammonia accumulates, the soil Ph drops, and you get a dead chicken yard situation: the collapse scenario. We want to avoid the collapse scenario. Summary insights What I took away from this academic excursion is:
Designing a chicken food forest that can use all the chicken poo. Collapse is a real danger in the chicken food forest because even with the chickens grazing on the berries, grains, and grubs produced in the forest, we will bring in outside food (and nitrogen!). According to the estimates made in the previous letter on overall chicken food forest design, the hens will be able to get between a quarter to a maximum of half of their food from the food forest in productive months. So, we need to ensure the design creates a balance between the input of outside nitrogen, rates of nitrogen use by soil life, and possibly removal (harvest) of materials that have nitrogen stored in them. Being a geek, I found out that you can calculate how many pounds of nitrogen your chickens are going to produce (it’s all online). Each hen produces 130 lbs. of fresh manure every year, 1.6% of which is the element nitrogen (N), or 2 lbs. of pure nitrogen per hen. Wowsie! We have a flock of roughly 100 hens, who together excrete about 200 lbs. of pure nitrogen per year. A refinement of the equation is how much of that is going to land in the c hicken food forest. The chickens will be in the food forest 8 months of the year – during which time they produce around 140 lbs. of pure N. In addition, they will spend the nights in the barn. Chickens poop during the night, and while I was not able to find information about exactly what percentage of their manure production is while they are asleep, a reasonable assumption is that production is constant through the 24-hour cycle. They are in the barn about 12 hours (from 8 PM to 8 AM) so that leaves 70 lbs. of pure N deposited in the chicken food forest per annum. On the other side of the equation is the size of the chicken food forest – which is 1/3 acre. That means the hens will deposit the equivalent of 210 lbs. of nitrogen per acre. This level is twice as high as what Robert Plamodon, an authoritative source on chicken pasturing says: “At a stocking density of 50 hens per acre, the hens will add 2.5 tons of manure per acre per year, equivalent to 106 pounds of nitrogen, 30 pounds of phosphorus, and 61 pounds of potassium. That’s about as much as most chicken yards can absorb unless you go to a lot of extra effort.” But of course, Plamodon is talking about maintaining chickens on a pasture of grass; whereas a chicken food forest is quite a different ecosystem. If you look up purely the nitrogen needs of grass pasture, lo and behold, it’s about 100 lbs. per acre, so Plamodon’s 50 chickens are hitting the sweet spot for his setup. Other crops, however, can have higher nitrogen needs. Here is a small list:
These calculations suggest we could be just perfect on the nitrogen front, but that it’s a little on the edge. Too much nitrogen can result in a drop in soil Ph so we’ll have to watch that and add lime if the Ph gets too low; and, as soon as we start to smell ammonia (indication of too much poo), add a thick layer of carbon (leaves, wood chips) to help decompose the manures. Or, we might also do well to throw in a bunch of tomato and corn seeds and let them do their nitrogen absorption thing! That was a long excursion, but I feel much more confident about the chicken food forest project now.
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Babette WIlsBabette is a permaculture farmer in Western Massachusetts. She and people who are working with her on the farm are experimenting and learning on the go. Archives
September 2024
CategoriesHappy 2024!It’s 2024 and we are excited for this coming year. Lots of plans: integrating trees and livestock in silvopasture; working with other farmers in the area to promote agroforestry and make it a viable farming option; expanding our berry patches; and of course continuing our offerings at the Greenfield and Turners Falls farmers markets with our partner Just Roots!
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