In the latter part of the 1800s during the homesteading of the Great Plains, farmers were for the most part successful because the weather was generally favourable. Severe drought conditions in the 1890s, however, shattered the illusion that life on the plains was necessarily good and drove out many settlers. This pattern of boom-and-bust farming recurred several times: good weather and high-production years were followed by periods of drought, economic ruin, and serious soil erosion. The worst drought and resultant soil degradation occurred during the 1930s in the area of the Dust Bowl. Average wheat and corn yields fell by as much as 75 percent. Worse, millions of tons of valuable topsoil were lost.
As a result of this climate-induced disaster, the federal government established the U.S. Soil Conservation Service to help farmers protect the soil. Decades later new crop strains better adapted to regional climates were developed, and irrigation and chemical fertilizers were made available to take advantage of the new genetic strains and to promote production. These advances, together with the development of such technological aids as tractors, mechanical harvesters, irrigation pumps, and agrochemicals (e.g., pesticides and herbicides), have increased the productivity (average yield of grain per harvested area) of the Great Plains by 200 to 300 percent since the 1930s. Total production (productivity multiplied by total harvested area) also has risen. In addition, the amount of year-to-year variability in yield, relative to the average yield, for most grains has decreased over time. Yet, while the relative variability (year-to-year variability as a percentage of long-term average yield) has generally declined for crops in recent years, the absolute variability (year-to-year variability in yield by itself) has increased on the whole in spite of all the technological advances.
This has led to an ongoing debate about the relative role of climate versus the role of technological advances in influencing both average-yield and yield-variability trends during the 1960s and '70s. While agrotechnology appears to have been the prime factor behind the general increase in annual grain yield, there is some doubt as to its actual contribution to the favourable decrease of variability in relative yield. Some investigators, most notably the American geographer Richard Warrick, have argued that this decrease cannot be entirely attributed to modern farming practices. Only if the weather anomalies of the 1960s and '70s had been as bad as those from roughly 1930 to the late 1950s could agrotechnology be credited with the reduced impact of climatic stress on crop yields. Warrick and his associates compiled an index of the severity of summer droughts in the Great Plains in the period 1931-77 (Figure 58), which indicates quite clearly that since the late 1950s weather conditions have not been bad enough to test the hypothesis that technological advances have truly reduced the annual variations of grain yield. Given this situation, it is risky to assume that modern technology in the "breadbasket" of North America can stably maintain yearly productivity.