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Dishing dirt on Earth's soils

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It wasn't surprising to see a small crowd at a Winnipeg event talking about dirt. After waiting so long for spring to arrive, those interested in the topic are more likely to be getting their hands dirty than discussing it.

The public screening of the British documentary Humus: the forgotten climate aid was taking place this week just as Manitoba farmers were literally starting to 'kick up the dust' and 'hit the dirt' putting this year's crop in the ground -- an eerie coincidence given the film's central theme.

Essentially, the soil scientists featured in this film suggest modern agriculture is killing our soils, as well as our climate. "Hidden away beneath our feet is the last, last chance for our climate," the narrator says.

This is a relatively new twist on the linkage between agriculture and global warming. The sector is credited with contributing between 17 and 32 per cent of greenhouse gas emissions globally.

But the decline of humus, not to be confused with the Middle Eastern dip made from chickpeas, refers to the generally declining health of the Earth's soils, most notably their ability to absorb and store CO2 by converting it into organic matter.

In other words, soil could be a powerful tool in stabilizing our climate. In its healthy state, it can store twice as much carbon as the atmosphere. But not the way we're going about things.

Definitions vary, but soil humus is related to its stability, texture, water-holding capacity and the amount of living organisms such as earthworms, nematodes, protozoa, fungi, bacteria and various arthropods.

It's only in the last 30 years or so researchers have started to characterize the soil as a living entity instead of a growth medium. People generally understood it was a bad thing if it blew or washed away, and farmers who watch such things have long associated healthy earthworm populations -- one of the soil species big enough to see -- with more productive soils.

But efforts to understand the connections between how we treat the soil, its health and our climate, have intensified along with the frequency of weather-related natural disasters. "Soil research is becoming a matter of survival," the film tells us.

It's hard to imagine counting such things, but it's been said one pinch of healthy soil contains up to one billion living organisms. The general consensus is there is more life on Earth below the surface than there is above.

The premise behind the documentary is the tillage and monoculture associated with modern agriculture destroy the soil's structure. As well, the focus on fertilizing plants with chemical fertilizers rather than feeding the soil kills the micro-organisms responsible for soil's natural fertility.

As one scientist described it, the soil serves as the plant's stomach. "If we overload the soil, it gets diarrhea and the plants have a problem."

The linkages between tillage and soil health are well-known. Prairie farmers are among the world leaders in the adoption of no-till farming, not only because it keeps their soil from eroding, but because they have seen continued improvements in productivity due to better moisture retention and fertility. This has increased the diversity of crops they are able to grow.

Crops grown in soil farmed under no-till methods have been shown to need less fertilizer. Some farmers are also citing a reduced need for pesticide weed control.

But the link between chemical fertilizer and declining soil health is bound to be met with skepticism and no small measure of resistance. Farmers need to replace the nutrients their crops remove from the soil and fertilizers offer a quick solution.

Building stable humus, or overall soil fertility so it can feed the growing plants, takes time and a radical change in land-management and cropping practices. City folks aren't absolved of responsibility either; attitudes toward composting need to shift away from a focus on waste management to soil building, humus advocates say.

Laura Rance is editor of the Manitoba Co-operator. She can be reached at 792-4382 or by email:

Republished from the Winnipeg Free Press print edition May 11, 2013 B10

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