Inland Northwest dust bowl: Half the topsoil of the Palouse is gone
The dramatic story of the Dust Bowl may be better known, but there’s a disturbing version of the same story in Eastern Washington. Roughly half the topsoil has disappeared from the Palouse since the arrival of the plow. Like the wide-open plains of the Midwest, the rolling hills of the Eastern Washington presented an ideal place for tractors that allowed farmers to work far more land than trailing behind an ox or horse. The economic and social trends that drove mechanization made it easier to plow more intensively and frequently, leaving bare ground vulnerable to wind and rain for much of the year. And as farms mechanized, soil conservation practices such as terracing, contour plowing, hedgerows, and trees planted for windbreaks became obstacles to maneuvering large machinery that could not follow tight turns on sloping land. So even in the aftermath of the agricultural debacle of the Dust Bowl, public and governmental awareness slowed but did not curtail soil loss in the Palouse. The pace of soil erosion was slow enough not to make headlines, yet fast enough to carry off a third to half of its rich topsoil in under a century. Soil erosion became an obvious problem soon after the Palouse was first plowed in the late 19th century. In the early 1900s, William Spillman of Washington State Agricultural College (later to be Washington State University) toured the region lecturing on the threat of soil erosion from the common practice of leaving plowed fields bare each summer. Few heeded the young professor’s warning that each year’s annoying rills would eventually add up to a major headache. Half a century later, a U.S. Department of Agriculture survey reported that all of the original topsoil was missing from 10 percent of Palouse farmland. Between one quarter and three quarters of the topsoil was missing from an additional 80 percent of the land. Just a tenth of the region retained more than three-quarters of its original soil. Annual surveys of soil loss from 1939 to 1960 showed an average loss of half an inch a decade, and four times that on steep slopes. Plowing the region’s fragile loess soils increased erosion ten to a hundred fold, with most of the loss from runoff across newly plowed ground. A cistern installed in 1911 on a farm near Thornton strikingly illustrates the effect of plowing sloping fields. Originally projecting about a foot and a half above the adjacent hilltop, by 1942 it stuck out nearly four feet above the surrounding field. By 1959, the same cistern stood six feet above the field. Four and a half feet of soil had been plowed off the slope in less than 50 years – about an inch a year. In 1979, the Soil Conservation Service reported that three decades of plowing had lowered fields in the Palouse as much as three feet below unplowed grassland. Berms of soil four to 10 feet high piled up at the downhill end of plowed fields. Experiments conducted with a typical 16-inch moldboard plow pulled along contours showed that plowing typically pushed soil more than a foot downhill. In addition, plowing exposes bare, disrupted soil to dramatic erosion when wind and rain storms ravage ground not shielded by vegetation. In this way, till-based agriculture can slowly strip soil off the land, as it did in Classical Greece, the Middle East, and other ancient civilizations. With modern technology, however, we can do it a lot faster. Soil loss does not have to happen. Simple soil conservation measures can effectively reduce erosion without reducing farm income, but doing so requires changes in farming practices. Over the past several decades, in the Palouse and other regions across the country, no-till farming has moved from wacky idea status to become an increasingly common farming practice – due in part to the rising cost of fuel for farm machinery. Similarly, organic farming practices also have been growing in popularity as experience shows they can be both as profitable and better for the land than conventional farming. In the mid-1980s, researchers led by WSU’s John Reganold compared the state of the soil, erosion rates, and wheat yields from two farms near Spokane. One farm had been managed without the use of commercial fertilizers since it was first plowed in 1909. The adjoining farm was first plowed in 1908 and commercial fertilizer was regularly applied after 1948. Surprisingly, there was little difference in the net harvest between the farms. Wheat yields from the organic farm were about the average for two neighboring conventional farms. Net output from the organic farm was less than that of the conventional farm only because the organic farmer left his field fallow every third year to grow a crop of green manure (usually alfalfa). Lower expenses for fertilizer and pesticides compensated him for the lower net yield. More importantly, the productivity of his farm did not decline over time. Reganold’s team found that the topsoil on the organic farm was about six inches thicker than the soil of the conventional farm. The organic farm’s soil had greater moisture holding capacity, more biologically available nitrogen and potassium, and more than half again as much organic matter as topsoil on the conventional farm. The organic fields also eroded slower than the soil replacement rates estimated by the Soil Conservation Service. The organic farm was building soil. In contrast, the conventionally farmed field shed more than six inches of topsoil between 1948 and 1985. The bottom line was simple. The organic farm retained its fertility, whereas soil on the conventional farm – and by implication most neighboring farms – gradually lost productive capacity as the soil thinned. Just 50 more years of conventional farming would be enough to lose the rest of the region’s original topsoil. The Palouse is not unique. Worldwide, over 2 billion acres of virgin land have been plowed and brought into agricultural use since 1860. Until the last decades of the 20th century, clearing new land compensated for loss of agricultural land. In the 1980s, however, the total amount of land under cultivation began declining for the first time since farming reached the land between the Tigres and Euphrates. In the developed world, the rate at which new (and generally marginal) land was brought under cultivation fell below the rate at which land was being exhausted. Although we use a little more than 10 percent of Earth’s land surface to grow crops, and another quarter of the world’s surface for grazing, there is little unused land suitable for either. About the only places left that could be used for agriculture are the tropical forests where thin, highly erodible soils at most could support just a few generations of farmers. That we are already farming about as much, if not more, of the planet as can be done sustainably makes the need to conserve our agricultural soils all the more pressing, both in the Palouse and around the world.