The dirt on soil loss
By Andrea Baird

Dirt gets no respect. We buy “dirt-cheap” used furniture at garage sales and punish our kids for ogling “dirty” magazines. But while we are buying, ogling, and punishing, dirt is keeping us alive. “[Soil] is the source of the energy and materials that made us,” says Ward Chesworth, an adjunct professor in the Land Resource Science department at Ontario’s University of Guelph. “We are a crop of the soil just as much as wheat or barley.” More than 99 percent of human food grows on the land, all of it rooted in the soil. But through erosion and degradation, we loose more and more soil everyday. As the soil recedes, a crisis looms.

Twenty-one percent of the world’s cultivated land is now so severely degraded that it is no longer fertile. It’s not a new problem; soil loss has plagued us since humans cultivated their first crops 10,000 years ago. Some of history’s earliest farmers, growing crops in southern Turkey, built flat terraces for planting so that rain wouldn’t wash the soil down the hillsides of their mountainous terrain. Today’s farmers have six billion mouths to feed, and increasing population has made soil loss a problem on a global scale.

Fertile soil can be lost in several ways. Most commonly, it is dragged off the land by erosion. When farmers loosen their fields by plowing or leaving bare land unplanted, wind and water are free to wear away the dirt. The farmer is left with nutrient-depleted soil, and less of it. “When you have soil erosion, you lose topsoil which tends to be the most fertile,” says Chi-Hua Huang, a soil scientist at the U.S. Department of Agriculture’s National Soil Erosion Research Lab.

Soil is also spoiled when salt concentrates in the upper layers of routinely flooded or over-irrigated land. When soil is saturated, salts that naturally occur deep in the land diffuse upward. Grains and corn – our primary food staples – can’t grow in salty soil. Once soil is ruined by salinization or removed by erosion, it can’t easily be replaced.

Soil erosion and degradation cause a host of problems that grow along with exploding populations in the world’s poorer nations. “In developing countries the loss of soil can cause significant amounts of productivity decrease,” says Huang. Poverty exacerbates soil loss by forcing people to strip away every scrap of plant material their land can produce. Farmers in sub-Saharan Africa...