Can chickens reverse climate change
I
summed up highlights from Meat
by Simon Fairlie over on my homesteading blog last week, but I wanted
to share one tidbit over here. The book explores when and how
meat-eating can be benign or actively good for the environment compared
to when our carnivorous ways are hurting the planet, and the author
commits a full chapter to considering rotational
grazing. The
idea is that carefully planned grazing schemes can sequester carbon in
the soil just like a woodland might, resulting in less carbon dioxide
in the atmosphere to fuel global warming.
Fairlie does a bit of
math and concludes that if we increased organic matter levels by 1.6%
in the top foot of soil in all arable and grazing land worldwide, we’d
pull enough carbon dioxide out of the atmosphere to drop air levels
back down to 300 ppm. And, at first, that seems very feasible
since large-scale gardeners and small-scale farmers often increase the
organic matter content of their soil by several percentage
points. For example, just
one year of grazing with chickens seems to have raised the organic
matter levels of one of my pastures from 4% to 5%.
Unfortunately, when
Fairlie delves into the scientific literature,
carbon sequestation in agricultural soil starts to look a bit
dicey. Although anecdotal evidence of soils turned black by
rotational grazing abound, scientists can’t seem to replicate the
results. Perhaps that’s because their studies rely on math to
determine when to rotate animals, and every grazier knows you have to
watch the grass and move your flock or herd based on biology. In
other words, hypothesis A is that the scientists are just doing it
wrong.
However, the lack of
scientific evidence could also be due to the fact that most rotational
grazing operations are only what Fairlie calls “half a farm.”
Nearly all of us are buying in feed, and it’s that input of energy,
organic matter, and nitrogen from elsewhere that adds to the organic
matter of our own farms. In essence, we’re just moving carbon
around, and may actually be causing a net release of carbon dioxide
into the air if we buy our chicken feeds from industrial farms that
lose more organic matter from the soil every year than we add back to
our farms with our own flocks.
So could we sequester carbon
with rotational grazing? Probably, if we played our cards
right. New data suggests that a protein called glomalin that’s
exuded by mycorrhizae may account for a quarter of all carbon
sequestered in agricultural soils, which points us toward boosting
fungal levels in the soil. Other studies suggest that roots are
more likely to turn into stable humus than top growth of plants, so we
can work on maximizing root production. (On the other hand,
another study puts into doubt the oft-repeated assumption by rotational
grazers that many grazing episodes result in plants producing and
shedding more root hairs — in one study, plants grazed once a year
produced more biomass and more soil carbon than those grazed five times
a year.) If you’re grazing cows instead of chickens, trampling is likely to drastically
increase your carbon sequestration, and we can all focus more on buying
in less feed from poorly-run operations.
Whether or not we can
reverse climate change with livestock, we can definitely integrate them
into our homesteads better so we cause fewer environmental catastrophes
elsewhere. I highly recommend reading Meat for much more information on
the science behind integrating animals into permaculture systems.