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Posted September 13, 2007: It can take as
little as three years to effectively burn your way through
most of the 50 to 100 tonnes of humified organic matter in
a typical acre of Ontario's corn producing soil. Once you
burn through that organic matter, however, it may realistically
take three lifetimes to build it back up.
That imbalance has Canadian soil specialists shaking their
heads in disbelief at some of the bio-energy concepts being
touted as representing the brave new world of renewable energy.
"If it burns up your organic matter, there's nothing
renewable about it," snaps a worried Keith Reid, soil
and fertility specialist for the Ontario Ministry of Agriculture,
Food and Rural Affairs (OMAFRA).
Those concepts, based on removing whole-plant top growth
from the field and not putting any organic residues back,
have the potential to zap the productivity out of today's
soils almost as quickly as turning off a light switch. But
they aren't the only plans that have soil scientists on the
alert. Even ethanol and biodiesel proposals that rely on corn
and soybeans will prove damaging to Ontario's long-term agricultural
productivity if high prices lure more acres into monoculture
and away from sound rotations, the scientists warn.
"There's no free lunch," says Ed Gregorich, soil
scientist for Agriculture and Agri-Food Canada at Ottawa.
"Organic matter is the key to soil productivity. If we
allow it to be depleted, there might be a short-term financial
gain but we'll be faced with compaction, poor soil structure
and a whole suite of other long-term soil quality issues."
In fact, it turns out that in order to maintain any hope
of sustainability, most soils have very little cushion. Now,
a team of OMAFRA extension specialists including Kevin McKague,
Adam Hayes and Christine Brown, has taken a first provisional
stab at calculating how much cushion exists.
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| editor's
NOTE: |
| U.S. readers
note that one metric tonne equals 1.1 U.S. tons,
and one hectare equals about 2.5 U.S. acres. This
means the carbon recharge rate cited here that is
necessary to maintain Ontario soil productivity
of 3 tonnes per hectare is about 2.2 tons per acre. |
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The OMAFRA team based their calculations on existing research
showing it takes 3 tonnes of carbon per year to simply maintain
the organic matter content of a hectare of moldboard-plowed
corn soil. (Carbon is the building block of organic matter).
Less carbon is needed in no-till soils, in part because of
lower erosion rates, but also because the mere turning over
of plowed soils exposes more organic matter to atmospheric
oxygen, where it undergoes chemical processes similar to combustion.
Even so, a no-till field still needs a carbon injection of
about 2.1 tonnes per hectare per year.
The OMAFRA team calculates that Ontario could only afford
to divert 2.7 percent of its corn stover to off-farm processing,
assuming that the spent stover isn't returned to the field
after processing. Even in years with growthy crops, such as
2005, the province could only export 9.5 percent of its stover.
With no-till, the stover available for harvest is higher,
but if growers hope to be sustainable in the long-term, they'd
be limited to selling a quarter of their corn residue, the
team says.
For other crops, the outlook is even more restricted. Not
surprisingly, there's essentially no room to export soybean
top growth, since soybeans produce so little organic material.
More surprising, though, is the team's conclusion that Ontario
also cannot afford to export wheat straw off-farm for energy
processing. That's because 450,000 tonnes are taken off for
straw, and that's already stretching the limits.
"We need to look at the soil as a finite resource,"
McKague says. "We haven't got a lot of organic matter
to spare."
Indeed, soil specialists generally applaud Ontario's grain
farmers just for being able to hold onto current organic matter
levels, following rapid declines in the '70s and '80s when
many farms gave up their livestock and therefore had no manure
source, and when they also aggressively moldboard plowed.
Progress has stalled, however. McKague points out that while
about half of Ontario's cash-crop soils are managed with conservation
tillage, less than 20 percent of cornfields are no-tilled,
and that number hasn't been growing.
"We won't be doing any favors for anyone, least of all
ourselves, if we damage that equilibrium just to grow energy
crops," McKague says. "None of us are against using
farms to grow energy. That's not what we're saying. But we
do need to get it right, using minimum tillage as much as
possible and not taking off more bio-materials than the soil
can sustain."
Like McKague, Reid thinks farmers need to draw the line for
themselves. "We're already seeing signs that some of
these promoters are either underestimating, or they're completely
ignoring the impact their plans are going to have on organic
matter," Reid says. "Fortunately, the farmers are
asking tough questions, and they're going to have to keep
on asking those questions."
Indeed, Gregorich says the best outcome for everyone—farmers
and consumers alike—may be to actually increase the
amount of organic matter in our soils. That would have the
double advantage, Gregorich explains, of boosting soil productivity
and lowering the level of climate-warming carbon dioxide in
the atmosphere.
Fortunately, Gregorich adds, scientists in the past decade
have vastly improved their ability to provide advice about
soil organic matter. Detailed studies are unraveling its complex
nature, delving into the roles of each of its myriad components
instead of treating organic matter, as in the past, as a single
uniform substance.
"Organic matter is going to be a critical issue, one
of the critical issues," McKague says. "Society
is saying it needs us to help diversify our energy future,
but we also need to look after the future of our soils."
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