Economics say all city dwellers must be vegan.

Toby Hemenway hemenway at jeffnet.org
Thu Mar 15 16:06:48 EST 2001


Joseph/Randy et al:

 I wrote the bit about how
>humanure couldn't function as the sole source of fertilizer since the nutrients
>would run out." 

Let me put it more clearly, a simple, idealized point: Growing only human
food plants and fertilizing them only with the residents' humanure and the
field waste from that garden won't work for long. There are constant losses
by the metabolisms of the humans and decomposers, plus soil leaching and
volatilization of nitrogen. You need other sources of nutrients. An analogy
would be trying to get all your water from your own purified urine: you'll
get less and less with  each round. Joseph's example adds cover crops to my
humanure-only scenario, which isn't what I said,  and changes everything.
Joseph makes the same point as I do: You need N-fixing and other cover
crops, or manure, grown at other times or on additional land.  These then
need to be transported and incorporated into the soil by humans, machines,
or-for us lazy, sustainable types--animals.

Some of these posts are confusing the food chain of crop-animal-human (or
crop-human) with the crop-to-soil cycle. Livestock, properly raised,
actually shorten the crop-to-soil cycle and can reduce losses. The
crop-to-soil cycle already contains animals, many layers of them. Bacteria
eating a leaf convert most of that leaf into CO2, then the bacteria get
eaten by (e.g.) amoeba, and the amoeba are eaten by mites, and mites by
beetles, beetles by spiders, spiders by birds, etc., with huge losses of
gases and water-soluble nutrients at each step. Finally a speck of soil
results, along with many times more C02 and other lost elements. If instead
that leaf is eaten by livestock that shits it out, the food chain is much
shorter, as the manure is (partly) directly usable by plants, and far fewer
nutrients are lost to the atmosphere and leaching. Much of the leaf is still
on the land, in the form of manure and  livestock. And I'll bet less is lost
than if it were composted: fewer iterations of the decomposer cycle.  I
think you need both systems to keep soil healthy and to maximize the yield
of the farm.

Composting and meat production are both animal-based processes; humus is
merely the manure and indigestible remains of soil animals (I've seen a
micro-photo of a half-rotted leaf covered with mite poop; looks like
cowpies). Soil building is tremendously inefficient. This is why a finished
compost pile is only about 20% the size of the original pile, a process not
much more efficient than the grain-to animal cycle (if I may confuse them).
You could consider livestock as one link in the decomposer chain, where the
yields go to humans instead of to soil.  If animals weren't an efficient way
to cycle nutrients, believe me, nature would have eliminated them long ago.
But obviously, industrial agriculture trying to support a bloated population
isn't what nature had in mind.

>[we shouldn't] pretend that an acre
>of animals on pasture will produce as much digestible protein as an acre of
>properly spaced, properly timed plants

That's absolutely true. If land is good enough to be cultivated, then grow
human food. But pasture is usually land too poor or distant to grow crops
(or should be!), hence will yield more for people when it has animals on it
as opposed to crops, unless the farmer makes heroic and unsustainable
efforts. 

I appreciate many of the points Joseph has made. If you are going to run
animals in a system (or even let wild ones wander through) they will have to
be managed, just as you manage plants. So decide if that's what you want to
do. A good permaculture designer isn't going to begin by saying "Well, I
want some cows: where will they go?" I would say, design your system to grow
crops directly for humans whenever possible, balance this with sufficient
plantings for habitat, fertility, etc, and fit livestock into this where
they are beneficial and can convert otherwise unused yields into products. A
good permaculture system should need few inputs. With a mature agroforest,
deep rooted trees will harvest nutrients from rocks and minimize leaching
loss. But you can always stack animals into this system to convert more of
its yields for human use, or just for plain diversity's sake.

And I love the screaming, confused, smirking carrot idea.

   

Toby




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