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No more mud pies?

October 3, 2008

Dirt. You probably haven’t given it much thought since your days as a mud pie connoisseur, but it’s time to start thinking about it again (although we don’t necessarily recommend adding it back into your diet). And why, pray tell, is dirt worth contemplating? Because we need it and yet we seem to be losing it faster than it can be replaced. Clearly, this is a problem.

Soil creation is a painfully slow process. On average, soil experts (grownups with degrees in this stuff, not toddlers with a penchant for pie) figure that it takes anywhere from 300 to 1000 years for every inch of soil to develop. Unfortunately, that inch can get washed away overnight in a hard rain.

So what’s the big deal about losing a little dirt? Well, soil is essentially the living skin of our planet, stretched over a skeleton of bedrock. It ranges from a few inches to a few feet deep, depending on where you are. And topsoil–the top layer of soil where roots grow–is where the magic happens. Without topsoil we wouldn’t have plants. And without plants, we couldn’t survive. So dirt’s kinda important, doncha think? 

Soil formation follows a pretty simple recipe: a dash of physically and chemically eroded rock, a pinch of accumulated windblown organic matter and a hint of chemical processes, all set to bake for 100,000 years or so. Nature’s not-so-secret ingredients, however, are the critters like bacteria, fungi, protozoa, nematodes, mites, bugs, and earthworms that make their home in the topsoil. These guys convert loose collections of dust, sand and rock into rich, productive soil that can support plant life. Take away all of those critters and you are pretty much left with boring old sand, rock dust and minerals.

The take home message? Without topsoil, plants can’t grow. But without critters, topsoil loses its mojo.

And mojo-less topsoil is what covers 7.5 million square miles of previously farmable land–that’s an area the size of Canada and the US put together. How did that happen? Predictably, we did it. Shortly after the Stone Age, humans began clearing land and overworking the soil all over the world. In some places (like cacao plantations in Central and South America) the soil has been over farmed to the point where it can no longer support life. Without the critters (or plants) to hold it together, soil is more susceptible to being blown away in the wind and washed away in the rain. And once gone it is very difficult to get back–remember the 100,000 year recipe? 

Soil is great when it’s on the ground, doing its job. But when wind or water move it around it can cause all sorts of problems. Airborne dust can lower air quality thousands of miles away from affected fields. And sediment from runoff and air-blown soils smothers coral reefs and other underwater habitats. In other words, farmers are doubly screwed. They’re losing their land, and now they can’t even fish for food.

To minimize this screwage, farmers in many parts of the world have begun using more sustainable practices. They’ve stopped tilling the soil between plantings and leave stubble from previous harvests in place–and they add compost. According to recent research, compost just might help soil keep its mojo. Researchers determined that early farmers in the Amazon basin enriched the quality of their soil using a mix of charcoal, food refuse and other wastes. The results of this hard-core composting are still apparent today: Some spots have soil that is more than six feet deep where a few inches is more the norm.

Composting can help enrich existing soils, but it can’t replace what’s been lost completely. Scientists estimate that as a planet, we experience a net loss of around 1% of our useful soil per year. One percent may not sound like much, but it is. By 2030, the world’s population will increase by an estimated 1.5 billion. According to the FAO (Food and Agriculture Organization of the United Nations), we’ll need an extra billion tons of cereal grains to meet growing demand–that’s 34% more than we produce right now. That’ll be pretty hard to do without any dirt.

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3 Comments leave one →
  1. Kerri permalink
    October 7, 2008 7:53 pm

    I really, really want to see one of your articles as the reading comprehension article on a standardized test, where they ask the student to explain what minimizes screwage.

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