Wednesday, June 30, 2010

Some thoughts about protein and nitrogen

As a food-loving, Peak-aware, agricultural scientist I worry a lot about a likely future of world-wide food scarcity.

And, as an ex-vegetarian, I have real (but limited) sympathy for the increasingly popular "save the planet, go vegetarian" movement. (My sympathy is limited because, environmentally, vegetarianism is just an efficiency measure that can't possibly "save the planet". To really save the world as we know it, we need to reduce the number of humans on the planet, quickly).

Nevertheless, although vegetarianism is limited in what it can achieve, I've been surprised and disappointed by what seems to be an increasingly vitriolic anti-vegetarian backlash, led by people like Lierre Keith with her 2009 book, The Vegetarian Myth.

The main problem I have with Lierre Keith is that she's a patronizing ignoramus who apparently knows remarkably little about the subjects she wrote an entire book on.

One of Keith's central tenets is that humans cannot live by eating plants alone. She's correct on this point, for the simple reason that vitamin B12 is an essential nutrient not produced by plants. The problem is that Keith's book is a 321-page rant, in which she bases many of her specific arguments on notions that have no basis in reality (I'll provide some specific examples in a minute).

However, The Vegetarian Myth has received an average rating of 4 out of 5 stars on Amazon, indicating that most of Lierre Keith's readers are so completely unaware of the basic facts about plants, animals, and nutrition that they find her arguments completely plausible. This is profoundly worrying to me.

If people eagerly absorb false beliefs about, for example, how many chickens can live sustainably on one acre of pasture; and if they have no idea where nutrients actually come from - then how can they possibly hope to feed themselves when relocalization is forced upon us all, courtesy of Peak Oil, and whatever other global catastrophes may await us?

The subject of human nutrition is way too big for one blog post, so I thought I'd focus for the moment on the subject of protein (which is probably still too big for one blog post).

In The Vegetarian Myth, Lierre Keith carries on about "poor-quality plant protein". She repeatedly compares animal protein with plant protein, and declares that animal protein is "better".

To say that animal protein is "better" than plant protein is to express a personal opinion. But, because many of Lierre Keith's beliefs and opinions are based on misinformation, I would argue that she has arrived at her conclusion via seriously flawed "reasoning".   

In fact, animal protein (from meat, milk, and eggs) is "complete", meaning that it contains enough of all the essential amino acids to support a human's total protein needs. However, complete protein can also be obtained from plants, very easily. A small number of plant foods (such as amaranth, buckwheat, soybeans and quinoa) provide complete protein on their own. Other plant foods have to be combined to provide complete protein. For example, common grains such as rice and wheat can be combined with legumes, vegetables, or nuts to yield a highly nutritious, complete protein meal.

Hence, for Lierre Keith to make the blanket statement that all plant proteins are "poor quality" is either ignorant or foolish (the irony here is that Keith delights in telling her readers - over and over again - how terribly ignorant vegetarians are).

Where does protein come from?

Proteins are made up of amino acid building blocks. Amino acids are molecules based on the general formula: H2NCHRCOOH. In other words, proteins are based on the elements:

Hydrogen (H),
Nitrogen (N),
Carbon (C), and
Oxygen (O).

Carbohydrates and fats are also based on hydrogen, oxygen, and carbon. Hence, the characteristic element that differentiates protein from the other macronutrients is nitrogen. Indeed, it is the nitrogen component of protein that enables scientists to use the so-called Kjeldahl method to estimate the amount of protein in a particular food, and "on food labels the protein is given by the nitrogen multiplied by 6.25, because the average nitrogen content of proteins is about 16%."

Lierre Keith actually mentions the importance of nitrogen, albeit in rather purple prose:
"This is the chemistry we should learn like a liturgy: life is spoken in the language of nitrogen. You’ve probably heard that amino acids are the building blocks of protein. Well, nitrogen is the building block of amino acids, the alphabet of DNA." (p.104)
Keith then briefly mentions the crucial fact that particular bacteria, in symbiosis with leguminous plants, "fix" atmospheric nitrogen into a form accessible to plants, and thence to animals. She states that "this is where essentially all the fixed nitrogen on the earth started" (p.105). She isn't quite right there. For example, cyanobacteria (blue-green algae) "inhabit nearly all illuminated environments on Earth and play key roles in the carbon and nitrogen cycle of the biosphere". Cyanobacteria operate independently of leguminous plants.

Keith explains that, to grow food, soil needs adequate nitrogen. This is absolutely true. However, she then leaps into la-la land by stating, repeatedly, that adequate nitrogen can come only from animal products, such as livestock manures and "what’s left of the dinosaurs". This is bizarrely, blatantly, totally incorrect.

Keith obviously hasn't pondered where the nitrogen in animal manure comes from in the first place. It's elementary: the nitrogen in cow poo comes from the nitrogen in the plants that the cow ate. You can obtain even more nitrogen by cutting the cow out of the equation completely (because the cow, of course, uses a significant amount of nitrogen to create the protein that you find in a steak):

Below I'll respond in detail to Keith's following statement about nitrogen and protein:
"Nitrogen, phosphorus, potassium - NPK - is the Triple Goddess of gardeners, the Troika of elements that rule plant growth. [...] Nitrogen was the big one. There are plants that fix nitrogen. Wasn’t that enough for my garden? Couldn’t it be? I begged. But I was begging a million living creatures who had organized themselves into mutual dependence millions of years ago. They had no use for my ethical anguish. No nitrogen-fixing plant could make up for all the nutrients I was taking out. The soil wanted manure. Worse, it wanted the inconceivable: blood and bones." (p.19)
There are at least two important questions to ask in response to Keith's emotional paean to animal-based fertilizers:

1) How much nitrogen does Keith's garden really need? And,

2) Where does the nitrogen in Keith's animal-based fertilizers actually come from - and where does it end up?


1) How much nitrogen does Keith's garden really need?

The answer to this question depends on several variables that are unknown to me, such as what plants Keith is trying to grow; how much water she has access to; and whether her garden is limited in nutrients other than nitrogen.

However, below are some ball-park figures for nitrogen requirements (in kilograms of nitrogen per hectare, or kg N/ha) for tomatoes, corn, wheat, and soybeans:

Tomato plants use ~100-150 kg N/ha, yielding 35-60 metric tonnes of fruit per hectare (reference).

Corn (maize) uses up to 200 kg N/ha, yielding 20 tonnes of corn, fresh weight (reference).

However, one 2005 study found that the overall economically optimum nitrogen rate for corn was 125 kg/ha.

Wheat uses ~95 kg N/ha, yielding 2.7 tonnes of grain (reference).

Soy uses 312 kg N/ha, yielding 3.4 tonnes of soybeans - however, typically ~50% of this nitrogen is fixed by the soy plants in symbiosis with bacteria such as Bradyrhizobium japonicum (reference).

Hence, it seems fair to say that high-yielding food plants generally require roughly 100-200 kg N/ha.

Lierre Keith claims that "no nitrogen-fixing plant could make up for all the nutrients I was taking out" - but she provides no data to support her claim. So I went and consulted Google, again.

According to a paper published by the University of Florida, symbiotic nitrogen fixation rates of "75 to 300 kilograms of N per hectare per year are common in various combinations."

And one study found that a leguminous green manure crop, "in general, supported corn yields equivalent to those achieved with 90 to 125 kg/ha of fertilizer N".

So, contrary to Keith's claim, normal symbiotic (legume-bacteria) nitrogen fixation rates are more than enough to make up for the requirements of common food crops - even notoriously nitrogen-hungry ones like corn; and even assuming that none of the corn crop (i.e. the stem and leaves) is returned to the soil as green manure or compost.

However, it's important to note that, to maintain adequate soil nitrogen levels, a leguminous green manure crop would have to be planted in lieu of a food crop about once every two to four years, depending on which food crops were being grown. This means that a truly sustainable farm could probably produce only 50-75% as much food as a typical, modern, unsustainable farm that relies on synthetic nitrogen fertilisers made from fossil fuels.  


2) Where does the nitrogen in Keith's animal-based fertilizers really come from, and where does it end up?

Keith writes emotively about how her soil "wanted manure. Worse, it wanted the inconceivable: blood and bones."

Keith is playing games here by anthropomorphizing her soil. In reality, it's Lierre Keith who "wants" these animal products for her soil. So, my question for Lierre Keith is: where does the nitrogen in her manure, blood, and bone come from in the first place?

Nitrogen is a chemical element. Cows can't make nitrogen, nor can they metabolise the molecular nitrogen (N2) which is in the air all around us. Rather, cows must eat nitrogen in a form that is bio-available to them. Grass is rich in bio-available nitrogen, which it gets from the soil. The soil gets nitrogen from nitrogen-fixing bacteria, which in turn get nitrogen from the air.

If you remove animal manure from the pasture where that manure was produced, you deplete that pasture of nitrogen. If you deplete the pasture of enough nitrogen, it will no longer be able to grow enough grass to feed a cow, meaning that you will no longer get manure for your garden, meaning that you'll probably starve to death if you don't wake up and realise that you can't eternally rob Peter to pay Paul without eventually sending Peter broke.

As for the question: where does the nitrogen in Lierre Keith's animal-based fertilizers end up? The answer is that a significant portion of it ends up in her excreta, which she (presumably) flushes down her toilet and thence into her local municipal sewage works. (Incidentally, according to her book, Lierre Keith lives in both western Massachusetts and Arcata, northern California - an odd cross-continental living arrangement for someone who preaches about sustainability and localisation).

Anyway, as it happens, Arcata's sewage processing facility is the well-known Arcata Marsh and Wildlife Sanctuary (AMWS).

So, what exactly happens to the nitrogen in the sewage that ends up at the AMWS? Basically, it gets turned back in dinitrogen gas (that is, the atmospheric form of nitrogen that plants and animals can't use). According to EcoTipping Points, two processes are of particular importance for nitrogen cycling at the Arcata marsh:

1) Dentrification: The conversion of nitrates found in wastewater by bacteria into nitrogen gas through removal of oxygen in the anoxic conditions found in the detrital layers of the wetland.

2) Nitrification: The conversion of ammonium to nitrates (which must happen in oxygen rich regions of the soil, usually near the clumps of vegetation) which can then be converted into nitrogen gas through dentrification.

It's possible that Lierre Keith captures the nitrogen in her effluent by using a composting toilet, but she certainly doesn't mention this in her book.

I use a composting toilet, and I think it's wonderful - but that's surely another blog post.

Friday, June 18, 2010

What they didn't teach me at university: Soil is Life.

I've spent a lot of time recently learning about the so-called Fertile Crescent: that once-fertile and super-diverse swathe of land across Iran, Iraq, Syria, and southern Turkey that we (Westerners) are now more likely to think of as lifeless, war-torn desert.

There is so much to learn from, and say about, the Fertile Crescent, that I hardly know where to start. So I thought I'd take Maria von Trapp's advice, and start at the very beginning ...


Agricultural scientists and farmers are often surprisingly slow to figure out what's good for the land that they profess to care so much about. Usually, they start by doing what's good for themselves, at least in the short term. For example, scientists do whatever research they can get funding for (meaning that their research is often driven by the interests of Big Business), while farmers grow species that produce high yields, and/or fetch high prices.

Sometimes a farmer comes up with a genuinely good idea - but the good idea is all too often sparked by a farm's declining productivity, caused by too many years of mining the land for every last drop of vitality. In other words: necessity is the mother of invention. 

Colin Seis's development of pasture cropping is a good example of this. "Pasture cropping" is the zero-till sowing of cereal crops into perennial pastures - a simple and logical farming method that has been hailed as revolutionary by farmers and scientists around the world (just Google the terms "pasture cropping" + revolutionary to see what I mean about the buzz surrounding this "novel" farming technique).

The fact that intelligent humans can get so excited in the 21st century over a technique that nature has been using for countless millennia is, frankly, depressing to me. I think we were kidding ourselves when we called our species Homo sapiens, which literally means wise man.

I have a rather nice piece of paper, given to me by the University of Western Sydney, which declares me to be a Bachelor of Applied Science in Systems Agriculture.

I first developed an interest in agriculture on one of my train trips out to western NSW to visit an aunt and uncle during school holidays. (That was back in the old days, when passenger trains actually ran out to western NSW).

Gazing out through the train window, I was alarmed by the gully erosion I saw in paddock after paddock. I didn't really know anything about soil or agriculture back then, but even as a child I could see that gully erosion was (for want of a better word) wrong. In other words, even a child could see and understand that our agricultural land was damaged and depleted.

What is gully erosion?
"Gully erosion occurs when water is channelled across unprotected land and washes away the soil along the drainage lines. Under natural conditions, run-off is moderated by vegetation which generally holds the soil together, protecting it from excessive run-off and direct rainfall.

Excessive clearing, inappropriate land use and compaction of the soil caused by grazing often means the soil is left exposed and unable to absorb excess water. Surface run-off then increases and concentrates in drainage lines, allowing gully erosion to develop in susceptible areas." 
I wrote recently about Deborah Bain and her agricultural propaganda-fest called Farm Day, whereby impressionable city folk are encouraged to believe that Australian farmers are "committed to enhancing and protecting the environment".

However, according to the NSW Department of Environment, my local catchment area (Central West NSW) has upwards of 12,500 instances of gully erosion. Interestingly, that figure is more than 20 years old, but the Department states that it is "still indicative of what is happening today".

Meanwhile, Dr Christine Jones writes (in an article titled How to build new topsoil, which is well worth reading in its entirety):
"In little over 200 years of European land-use in Australia, more than 70 percent of land has become seriously degraded (Flannery 1994). Despite our efforts to implement 'best practice' in soil conservation, the situation continues to deteriorate.

Annual soil loss figures for perennial pastures in Tablelands and Slopes regions of NSW generally range from 0.5 to 4 t/ha/yr, depending on slope, soil type, vegetative cover and rainfall (Edwards and Zierholz 2000).

These figures probably underestimate the total amount of soil lost. Erosion can occur at much higher rates during intense rainfall events, particularly when groundcover is low. Areas which have been cultivated (whether for pasture establishment or cropping) are more prone to soil structural decline."
In light of these facts, I really wonder how people like Deborah Bain can stand up in public, and, with a straight face, claim that farmers are "enhancing" the Australian environment? As I've acknowledged before, there are exceptional farmers who are passionate about regenerating Australia's soils - but the key word there is "regenerating", meaning that they're attempting to re-build the soil and biodiversity which has been lost over the previous 100 years or more.

It's a rare farmer indeed who runs a commercial farming enterprise on land which is currently in better health than it was prior to European settlement.

And this brings me back to my experience of studying agricultural science at university.

Straight out of high school, I spent two unhappy years studying agricultural science at Sydney University. I sat through seemingly endless lectures on chemistry, physics, economics, and statistical data management. I found almost all of the course material mind-numbingly irrelevant to my interest in the land.

I found the course at Sydney University to be far too reductionist for my personal taste. (I'd probably get a lot more out of it now than I did as a teenager, but the simple truth is, I don't easily relate to soil, plants, and animals on a molecular level). My friends who thrived in that course went on to write academic papers with esoteric titles such as "Modelling soil attribute depth functions with equal-area quadratic smoothing splines".

After two years of fairly hard-core science and mathematics, I transferred over to the "Systems Agriculture" course at the University of Western Sydney (UWS). The course at UWS was as holistic as the course at Sydney Uni had been reductionist. At UWS we studied subjects like "Human Activity Systems", and our lecturers were big on concepts such as "praxis" (the process by which a theory or skill is enacted or practised).

I had a blast at UWS. I loved that course, because it allowed me to go and knock myself out with "praxis" in extraordinary places, as diverse as the Bayswater Colliery in the Hunter Valley; Warrah biodynamic farm on the outskirts of Sydney; and Kanchanjangha Tea Estate in the foothills of the Himalaya in Nepal.

Life at UWS was one amazing and life-changing experience after another. But the UWS course was critically short on science, and students who weren't smart and/or motivated could fairly easily cruise through the course without learning anything much at all.

So, the course at Sydney University taught its students to revere pure science, while the course at Western Sydney taught its students to revere farmers - but no one taught us to revere the land, the soil, the water, that every single one of us depends on for our lives.

No one taught us that soil is life. Indeed, how could they teach us that, when almost every aspect of agriculture concerns itself with controlling (and usually destroying) the soil food web? We were not taught to observe and respect the land; we were taught, instead, to "master" it, by grazing, ploughing, fertilizing, and irrigating it. We were taught to exterminate a staggering array of "pests" (ranging from fungi to kangaroos), with never a thought given to what crucial role those "pests" might play in the ecosystem.

We were taught to manage, to control, and to subdue nature. (Ha!)

We call ourselves Homo sapiens, but I think a more apt title might be Homo arrogans, or perhaps Homo insciens. As a species, we seem utterly incapable (or are we just utterly unwilling?) to learn from nature, and from our mistakes. As a species, we are apparently not as clever or as wise as we think we are.

Sunday, June 13, 2010

How big is a chicken's footprint?

I've been thinking about chickens a lot recently.

I would dearly love to raise my own chickens for eggs and meat. But if I raise chickens, I want to do so not just humanely (which is relatively easy), but also as sustainably as possible (which is a much bigger challenge).

Total sustainability implies a closed, self-supporting system that can operate indefinitely without taking inputs from elsewhere. A closed system would, for example, provide all of the nutrients and dietary supplements (including grit) that a chicken needs in order to be healthy and productive. It would also provide all housing materials.

Modern domestic chickens are the descendents of Red and Grey Junglefowl, which evolved in the tropical forests of Asia. Generally speaking, the further removed a chicken is from its native tropical forest environment, the more dependent it will be on its human keeper for food, shelter, and protection.

The first major problem I have with creating a sustainable chicken-raising operation is that my "system" (my land) is only two acres in size. So, the first question I asked myself, before eagerly rushing out to buy some chooks, was: how much land does one productive chicken need?

I may as well have asked myself: how long is a piece of string? The answer to the chicken question depends on a large number of variables, including: what is the local climate like? (Is the land bountiful? Is it prone to drought? Is it under snow for several months of the year?). And what exactly is a "productive" chicken, anyway? (Is it one that produces an egg every day? Or is it one that simply performs some basic weed control?) The questions go on, but I'm sure you get my drift.

So, I started Googling, and (as my favourite blogger noted at the time) I found a figure that has surprised everyone I've mentioned it to: the general consensus seems to be that a 100% free range chicken requires roughly half an acre of land in order to meet all of its requirements. 

Most of the people I've mentioned this "Chicken Footprint" to have responded with incredulity; even (or perhaps especially) the people who actually raise chickens - although I'm yet to meet a chicken owner who maintains even one healthy chicken without buying supplementary feed or additives of some description.

(As an interesting side note, some local friends mentioned that the monetary value of the chicken feed they buy actually exceeds the monetary value of the eggs they get from the half-dozen aging hens in their backyard).

Lierre Keith, author of The Vegetarian Myth, touches very briefly on the chicken footprint concept in Chapter 1 of her book. She writes:
I’ve heard vegetarian activists claims that an acre of land can only support two chickens. Joel Salatin, one of the High Priests of sustainable farming and someone who actually raises chickens, puts that figure at 250 an acre. Who do you believe?
Keith heavily implies that her readers should unquestioningly believe that one acre of land can sustainably support 250 chickens. Unfortunately, she provides no data or reference to support her belief. However, if she had bothered to read Joel Salatin's own book on the subject of raising pastured poultry, she would realise that her belief is, quite simply, wrong.

As an aside, it's interesting that Lierre Keith refers repeatedly to Joel Salatin as a "high priest". Unfortunately, her belief in Salatin's ability to squeeze truly miraculous levels of productivity out of one acre of land seems faith-based rather than fact-based. Maybe Salatin should capitalize on the religious-style fervour he stirs in people, and start a new cult:

Joel Salatin, the Messiah of Meat Lovers

As it happens, I own a copy of Salatin's book, Pastured Poultry Profits. The book (which is widely regarded as the best source of information about raising chickens on pasture) was first published in 1996, and was most recently updated in 1999.

The crux of the matter is this: "chickens cannot be totally grass-fed, according to several experts. They also need grain." (Ref: Chicken Feed)

Why can chickens not be totally grass fed? Because chickens are omnivores; they are not grazing, grass-eating, specialist herbivores. By contrast, sheep, cattle, and geese are physically adapted to thrive on a diet of 100% grass.

It is no coincidence that it is primarily omnivorous farm animals - pigs and chickens - who have ended up suffering the intensive confinement of factory farming. Why? Because pigs and chickens "destructively" dig up pastures in search of highly nutritious sub-surface critters and other goodies, such as roots.    

As it happens, even Joel Salatin's "pastured" chickens are mostly grain fed. According to Salatin, "the prepared ration represents 80 percent of the [pastured] bird's diet". He goes on to explain that 92% of the prepared ration he feeds his chickens is made up of annual grains, specifically:

Corn - 52%
Soy  - 29%
Oats - 11%

"So what?", you might ask.

The point is that, based on average US yields of corn, soy, and oats, you can't actually grow enough grain on one acre to feed 250 chickens (even assuming the chickens are getting 20% of their feed from pasture). And even if you could grow enough grain on one acre, where would those 250 chickens be living while you grow the grains to feed them (keeping in mind that corn, soy, and chickens all share the same spring and summer growing period)?

Following are the assumptions I used to calculate roughly how much grain it would take to feed Salatin's 250 Cornish Cross chickens for 6 months (which is how long Salatin raises broilers for each year).

The Cornish Cross is a large, fast-growing meat breed of chicken, which, in addition to fresh pasture, eats about 150g of feed per day (reference: Washington State University). Multiplied by 250 birds, that's 37.5kg of grain per day. Multiplied by 182 days (i.e. 6 months), that comes to a total of 6.8 tonnes of grain per year.

Broken down by grain (according to Salatin's feed mix), and using average US yield data, that's:

3.5 tonnes corn @ 4130kg/acre = 0.85 acre
2.0 tonnes soy @ 1188kg/acre = 1.68 acres
0.7 tonnes oats @ 1900kg/acre = 0.37 acres

TOTAL = 2.9 acres - just to grow the necessary grain to feed 250 birds for six months.

Then there's the acre of pasture that these chickens need to actually live on, bringing us up to 3.9 acres thus far, which equates to a substantially reduced figure of 64 birds per acre. If you subtract Salatin's average broiler mortality rate of 7.5%, you're down to 59 birds (Cornish Cross chickens are susceptible to having heart attacks late in the season, so you can't realistically expect to make a proportional saving in feed).

But that's not the end of the story by a long shot.

Salatin's super-productive system relies on the highly-controlled confinement and movement of (to use Salatin's words) "race car chickens". The Cornish Cross is a hybrid chicken which is "constantly being genetically upgraded by the commercial industry to perform at a totally unnatural gain rate" (also Salatin's words, ref: p.32). 

Salatin places his broilers in moveable pens which provide a space, on average, of less than two square feet per chicken. In this respect, it's worth noting that Salatin's broiler operation meets one of just two criteria which define a CAFO (a.k.a Concentrated Animal Feeding Operation, a.k.a a factory farm). Specifically: the animals are confined for at least 45 days in a 12-month period. 

Now consider some of the inputs, other than grain, that Salatin draws on to raise his pastured poultry (the following are all specifically mentioned in Salatin's book):

* live chicks from a commercial hatchery
* wood shavings for chick bedding (Salatin's chicks live on a floor of wood shavings for 12 to 28 days of their 56-day lifespan. Salatin raises multiple batches of chickens each season).
* artificial heat source to keep chicks warm
* drinking water
* feed and water containers
* hay chaff
* moveable pens (made from treated softwood, aluminum sheeting, chicken wire, screws, etc)
* plastic buckets (as Salatin says: "the world revolves around 5 gallon buckets")
* grit (creek sand and aggregate)
* feed grade limestone
* mineral supplements
* fish meal
* kelp meal (from Iceland)
* commercial probiotic
* cattle for keeping the pasture short before and after the chickens pass through
* tractor and fuel for transporting feed, water, and chickens.

Could anyone (besides Lierre Keith) seriously claim that all of these materials can be sourced sustainably from one acre of land? With room to spare for the actual pasture-fed chickens?

Furthermore, key factors that Joel Salatin's broiler system doesn't concern itself with at all are:

* Breeding: Salatin buys his chicks from a commercial hatchery. The poultry hatchery industry is a form of factory farming whose collective harm goes way beyond the scope of this blog post.

* Incubation: Salatin's system is based on artificial incubation, and the controlled confinement of all broilers, at all times.

* Winter care for birds: Salatin only keeps broilers for six months of each year, which is convenient for him, because Polyface Farm gets deep snow over winter. Chickens evolved in tropical jungle, so they don't cope well with snow. They certainly can't be expected to utilize fresh pasture for food during snowy winters. Hence, you would have to double the amount of land, or halve the number of chickens, in order to produce enough feed to keep the birds alive for an entire year. This brings us down to fewer than 30 birds per acre, or less than 12% of the stocking rate suggested by Lierre Keith - and that's still completely ignoring all of the inputs in the list above.

Having thought long and hard about this issue, I suspect that a chicken probably needs more than half an acre, assuming that your environmental accounting is unflinchingly honest (by which I mean that all inputs, including timber, fossil fuels, metal and plastic, as well as feed supplements such as fish meal, grit, and Icelandic kelp etc, are recorded in the ledger).

So. I think I can justify keeping a few chickens, even though creating a closed chicken-raising system on my two acres remains a pastoral fantasy. But, at the very least, I'm quite convinced that a pastured chook would have a happier life than a factory chook; and happiness counts, in my ledger.