Dirt: The Erosion of Civilizations - Kootenay Local Agricultural Society

years. Present rates of erosion, however, ranged from about an inch every
decade to half an inch a year. Based on the discrepancy between rates of
soil formation and modern erosion rates, they estimated that it would take
between two and ten centuries to strip Kenya’s gentle slopes to bare rock.
Soil erosion can destroy the vitality of the land—but land can be healed
too. Some subsistence farmers in Nigeria made a few simple changes and
transformed their fields—at no cost. Tethering their sheep and feeding
them crop stubble instead of letting them wander freely allowed collecting
manure to fertilize the next crop. Planting cowpeas as part of a crop rotation
also helped enhance soil fertility. Low earth-and-stone walls built
around the fields kept soil from leaving in heavy rainfall. Crop yields doubled
or even tripled without chemical fertilizer. What was required was
labor—exactly what subsistence farmers can afford to give. Labor-intensive
techniques that restore soil fertility turned the liability of a dense population
into an asset.
Ethiopia provides another example of how human societies more often
bring soil erosion with them. Medieval deforestation of the northern portion
of the kingdom triggered such extensive erosion in Tigre and Eritrea
that the hillsides could no longer support grazing animals. By about ad 1000
the economic impact of soil degradation forced the kingdom to relocate its
capital to better land in the south. There the process was repeated, as extensive
soil erosion followed widespread deforestation. The region remains
impoverished, unable to feed itself when the weather doesn’t cooperate.
Drought-triggered crop failure brought starvation to almost ten million
people in Ethiopia in the mid-1980s. Hundreds of thousands died despite
the largest global famine relief effort in history. Long before the twentieth
century, farming had expanded from the best agricultural lands onto
erosion-prone slopes. Since the 1930s, deforestation left Ethiopia with just
3 percent of its original forest cover and increased the silt concentration in
the Blue Nile fivefold. The average rate of cropland soil loss in the western
highlands would erode the native topsoil in little more than a century. In
addition to direct losses to erosion, soil fertility has been projected to fall
by as much as 1 percent annually owing to persistently intensive cultivation
by desperate farmers.
Ethiopia’s environmental refugee crisis shows how, over the long run,
soil security is national security. Recognition of Wangari Maathai with the
2004 Nobel Peace Prize for her work on environmental restoration in
Ethiopia’s countryside shows that environmental refugees, who now out-
dust blow 169