Mining of Soil
Mining is a process we generally think of as applying to the extraction of nonrenewable resources. What happens when people begin to mine the soil upon which agriculture depends? The answer is obvious; they convert agriculture from a renewable to a nonrenewable resource.
Unfortunately, the mining of soil has been going on in recent years in the United States and elsewhere in the world, according to Lester R. Brown, an acknowledged American expert in world food production. In an article in the November 27, 1981 issue of Science Brown notes that soil forms by natural processes at a rate of about two to five tons per acre per year. If agricultural practices cause erosion of more soil than is being formed, then the soil is being 'mined'.
Typical topsoil may be about eight inches thick and weigh about 160 tons per inch of thickness per acre. Hence, a typical acre would contain about 1,280 tons of fertile topsoil. Measurements made in Missouri indicate that agriculture involving a three-year crop rotation of corn, wheat and clover causes a loss of about 2.7 tons of soil per acre. This loss does not exceed the rate of new soil formation, so such agriculture can continue indefinitely. However, when the practice is to repeat the corn crop each year, the Missouri results show a loss of 19.7 tons per acre per year, and that means the soil is being mined.
The erosion story is the same elsewhere: Tennessee, Mississippi and Iowa are currently losing topsoil at rates ranging from 10 to 15 tons per year through water erosion caused by heavy cropping practices. Wind erosion in Colorado annually claims an average of 8.9 tons, and in Texas it blows away 14.9 tons per acre. The loss of topsoil through erosion in the Soviet Union appears to be even greater than in the United States, according to Brown. Some Third World countries, for example Ethiopia, are in deep trouble because of soil erosion.
Increasing world demand for food was met prior to 1950 by expanding the land area in production. Between 1950 and 1971 the world's farmers doubled grain production--not by increasing planting acreage, but rather by more intensive farming practices, the practices that contribute to increased soil erosion. The farmers were able to more than keep up with demand for food up to 1972. Since then, they have only been able to barely keep even with the needs of a growing world population.
These trends both bode well for northern agriculture and spell out a warning message. The increasing demand for food should improve the economic situation for northern agriculture, making it easier for northern farmers to compete with those elsewhere. However, as more northern land is put into agricultural production, there must be care not to use practices which cause soil to be lost faster than it is formed.
Preliminary work done on the new Delta barley project in interior Alaska indicates a slow soil formation rate there, and that annual soil loss rates should not be allowed to exceed two tons per acre. Yet in one isolated instance up to approximately 800 tons per acre was lost in one year's wind erosion. Parts of the project area evidently experience little wind, but other parts receive much. Clearly caution is in order. Without proper care, Alaska's barley can be like Alaska's gold, a nonrenewable resource.
