Soil

The earth beneath our feet is not something we often give much thought to, yet we cannot easily live without it. Good soil is the basis of agriculture, and therefore of most of the food that we eat. Healthy soil is not just dirt, but a complex community of microorganisms, fungi, plant roots, and animals of many sorts from soil mites to earthworms. It provides many ecosystem services including storing carbon, recycling nutrients, retaining and purifying water, and maintaining the balance of many biogeochemical processes. Soil is continuously being created through the decomposition of the underlying rock at a rate of about one ton per hectare per year, but also lost through erosion at the surface from wind, rain and moving water. Forested areas and others covered by natural vegetation tend to build soil slowly by holding it in place and adding organic matter. When vegetation is cleared and the soil is bared, erosion can be many times faster than soil formation, and the good topsoil diminishes and can ultimately be lost. As long as some topsoil remains, the loss may not be apparent, until suddenly productivity collapses when the last topsoil is gone.

Great civilizations have always been built on productive agriculture, and have collapsed if they did not take care to maintain the soil on which that agriculture was based (Montgomery, 2007). The Mediterranean basin was the granary of the Roman Empire, but the denuded hillsides and barren plains around the Mediterranean today help to explain why the empire collapsed.

Today our growing human population and intensive mechanized agriculture are putting unprecedented demands on all the soil resources of the world. In Indiana, USA, for every ton of grain harvested, a ton of soil is lost. Soil conservation efforts have slowed the loss in some places but not reversed it. The same thing is happening on a global scale. Since 1945, moderate to extreme soil erosion has degraded 1.2 billion hectares of agricultural land, equivalent to the size of China and India together. The amount of agricultural land abandoned in the last 50 years is equivalent to that farmed today. Every year, 75 billion metric tons of soil are lost from farms, and 12 million hectares of arable land (1% of the total) can no longer be farmed, resulting in the degradation of 38 percent of global cropland since World War II. Average global soil loss is ten to a hundred times faster than soil formation (Montgomery, 2007, p. 174).

Where soils were originally thick, as they were in many grain-producing areas, farmers do not see the effects of soil loss immediately, and artificial fertilizers have been able to maintain or even increase productivity. Soil conservation efforts may lower farm income, so the economic incentives are wrong. From a short-term economic perspective, there is nothing to worry about. But soil loss represents the consumption of irreplaceable natural capital, and the future ability of the planet to support a human population. It is a critical and under-appreciated dimension of our present unsustainability.

The longer-term solution lies in alternative forms of agriculture that combine food production with soil maintenance or enrichment, including no-tillage farming, some types of organic agriculture, mixed cropping and agroforestry. These are generally more labour intensive and cannot easily compete with our present fossil-fuel-subsidized intensive agriculture. The challenge is to produce sufficient food through such methods to maintain our human population at a reasonable standard of nutrition. More research is needed on such new forms of agriculture. Changes in consumption patterns, lifestyles and communities will be required to build a civilization that maintains and even increases its soil capital and lives only off the interest.

Montgomery, David R. 2007. Dirt: The Erosion of Civilizations. Berkeley, University of California Press. 286 p.