Ecological Crises of Modern Agriculture

POLLUTION, DEPLETION, DEGRADATION, erosion, contamination, poisoning—these are terms usually associated with heavy industry and cities, not with our green countryside of fields and scattered farmsteads. But these are all terms that are applicable to the environmental problems caused by conventional U.S. agriculture today. Agriculture has become very like traditional manufacturing industries, with many of the same environmental risks and waste-disposal problems among its side effects. This analogy has a dangerous flaw: because of agriculture's extensiveness and its use of toxins that are broadcast into the environment, its impacts are more wide-ranging than those of most other industries. In fact, they are so widespread that they are generally overlooked. This chapter explores the major ecological problems of agriculture: soil erosion, loss of genetic and biotic diversity, depletion of energy and water resources, chemical contamination of water, workers, and food, and creation of new and more serious pest problems. The breadth and seriousness of these problems present strong evidence that current agricultural practices are ecologically unsustainable.

DAMAGE AND DEPLETION

Despite major awareness stirred up by the Dust Bowl of the 1930s, and more than fifty years of research and government-sponsored soil conservation programs, modern agriculture has failed to produce a system that sustains its own capital—the living soil. Each year more topsoil slips away, down the earth's rivers to the sea. With each harvest, more soil is used up than is rebuilt, as, in effect, the soil is mined from farm fields. Likewise, the other pieces of our agricultural resource base—genetic diversity, fossil energy supplies, and water sources—have been damaged or depleted. In North America this exploitative approach produced the bounty that permitted the rapid colonization and development of an affluent society. Now that humankind has colonized the whole earth, however, people can no longer abandon spent fields and just wander off looking for new soil. As a society we must face the price of our wastefulness and the limits of the planet's ecological foundations.

EROSION

On the hopeful side, soil can be improved, even restored, given enough time. Soil-building processes can be enhanced, and remaining soil can be protected from further erosion. It is not a hopeless problem. But for anything to improve, society must first recognize the seriousness and magnitude of the problem.

On the Farm. Soil erosion increased at an alarming rate in the 1970s. Encouraged by booming export markets and federal farm programs, farmers removed shelterbelts, grassed waterways, and terraces so that they could plant fencerow to fencerow. As millions of acres of erosion-prone land were brought into production, erosion rates rose dramatically. In 1977, the Soil Conservation Service (SCS) initiated the National Resources Inventory (NRI) to document just how much soil was washing and blowing away. They found that, on average, the country was losing 1.8 tons of soil per acre (4 metric tons per hectare) in excess of the "officially tolerable" average annual replacement rate ("T") of 5 tons per acre (11 metric tons per hectare).

In 1982, SCS repeated the NRI, using more comprehensive methods, and came up with even gloomier figures. More highly erodible land had been brought into production during the five years between surveys, and the average loss per acre from croplands was now 8 tons per acre (18 metric tons per hectare), or 3 tons (2.7 metric tons) above T. That meant that 3.4 billion tons (3.1 billion metric tons) of soil were being washed or blown away each year. And that occurred in spite of the fact that acreage farmed with conservation tillage, which reduces erosion, nearly tripled during this period.

Although a small proportion of the cropland accounts for most of the erosion, the majority of the cropland is affected at some level. Twenty percent of U.S. cropland is subject to serious erosion, but fully one third (118 million out of 350 to 400 million acres, 48 million out of 142 to 162 million hectares) is classified as "highly erodible land" (HEL) under the conservation provisions of the 1985 farm bill. The HEL designation means that the land is highly vulnerable to erosion when cropped. While the Conservation Reserve Program (CRP) is removing some HEL cropland from production (25.5 million acres, or 10.3 million hectares, of the pool of 118 million acres, or 48 million hectares, as of February 1988), it is not yet clear how effective this has been at reducing erosion. Regions with the largest acreage of HEL cropland had low enrollment in CRP as of February 1988. For example, only 3.6 million acres out of a pool of 19 million acres (1.5 million hectares out of 7.7 million hectares) HEL in the Corn Belt were enrolled.

Tolerated Losses. What do these sobering figures mean in terms of the depth of soil lost, the productivity sacrificed, and, more importantly, the land's sustainability? The first step is to translate soil loss from tons into inches. It is generally recognized that deeper soils can sustain productivity longer than shallower soils. They can withstand more erosion before they will show much loss in productivity. In Iowa, where soils were deep to start with, it took a loss of 10 inches (25 centimeters) of soil to reduce corn yields by 50 percent. On shallow soils in Nigeria, a loss of only 2 inches (5 centimeters) cut corn yields in half. It takes from 300 to 1000 years for an inch (2.5 centimeters) of soil to be formed naturally. When agriculture causes soil loss to proceed much more rapidly than soil building, the system is literally losing ground; it is an unsustainable system.

If you removed the top inch of soil from an acre of land, it would weigh about 160 tons (145 metric tons). That means that at the national average rate of loss of 8 tons per acre (18 metric tons per hectare) each year, an inch of soil from the average acre of cropland is lost every twenty years (or 1 centimeter every 8 years). That may not sound like a particularly dramatic rate of loss, but when compared to the soil formation rate (300 to 1000 years per inch, or 120 to 400 years per centimeter) it becomes obvious that erosion rates are well beyond sustainable loss. Furthermore, erosion is much higher than average in some regions. At the rate of 100 tons per acre (224 metric tons per hectare) that is lost on some slopes (in some years) in the wheat-growing region of the Palouse in Washington State, it would take only 1.6 years to lose an inch of soil. The average acre in this region loses an inch of soil about every twelve years (14 tons per year, or 12.6...