Manure Matters on the Great Plains Frontier

American farmers followed a long-term sequence of clearing land, farming it for several decades, and then abandoning it in favor of new land elsewhere. For 300 years, farmers moved across the continent until they reached the Great Plains, and the end of the frontier, in the 1870s. Fertility and crop yields declined for fifty years by the 1930s, an agricultural crisis was looming. Only the adoption of synthetic fertilizer after World War II allowed farmers to continue annual cropping.