Manure Matters on the Great Plains Frontier

Historians avoid horse manure. Why, for example, should anyone care that for four days in May 1886 Kansas homesteader Elam Bartholomew shoveled out his barn, loaded manure into an old farm wagon, and hauled it to his corn field? Bartholomew himself did not consider the project an important event, noting tersely in his journal, "hauled out manure." But upon reflection, he might have admitted that it was, and not only for the sake of general hygiene on his farmstead. Farmers make their living by slightly altering nature to achieve human ends. They begin with natural components—soil, sunlight, rain, and plants—and convert them into usable products. They convert solar energy into food energy, in the form of wheat and beef; they shift water from rain to soil to plants; and, crucial to this story, they convert soil nutrients into food that builds and sustains human bodies. In short, the farmers' metier has everything to do with flows of energy through ecosystems, fluxes of hydrology, and the invisible transference of nitrogen from air to soil and back again. Bartholomew would not have spoken in these terms—he lived when the science of ecology was in its infancy—but he could have explained how much manure matters.¹

Manure was one of the few vectors by which farmers could increase the fertility of their land. Farmers manage the nitrogen exchanged between natural systems and human necessity. Despite the wide variety of plant life on earth, the same sixteen elements comprise the basic building blocks of most plants, whether buffalo grass, big bluestem, or barley. Plants exist as an intermediary between two storehouses of nutrients—soil and atmosphere. Plants pull nutrients out of the air and direct them to living pathways and into the soil. Alternatively, they pull them from the soil, direct them toward life processes, and return them to the atmosphere. Allofthis shuttling of nutrients from ground to sky and back is powered by solar energy through photosynthesis. All animals, including human beings, rely on these temporary diversions of nutrients from the earth and air. Farmers' manipulation of these nutrient flows is one of the most important stories of the past 10,000 years.²

Managing the Nitrogen System

In practice nitrogen (n) is the element most likely to limit plant growth. It is essential to plants, yet not readily available to them in soil. Air contains 78 percent nitrogen. Nitrogen surrounds wild plants and crops; tons of it float in the air directly over fields and forests. But plants cannot assimilate atmospheric nitrogen directly. They rely on the beneficent transformation of molecular nitrogen into forms that they can absorb and process. That job falls to microorganisms that transform molecular nitrogen in the atmosphere into ammonia and nitrate for which wild plants compete. Farmers work to divert available nitrogen toward crops that they grow for human purposes.³

The settlers who filled the U.S. Great Plains between 1870 and 1920 faced a challenge common to all farmers at all times, fertility maintenance. But stirring the soil, whether with hoes, horse-drawn moldboard plows, or mechanical cultivators pulled by diesel tractors, always diminishes the nutrients necessary for plant growth. Through 10,000 years of farming on five continents by hundreds of diverse human cultures, only a handful of solutions to soil fertility maintenance have emerged.⁴

One of the earliest solutions was to farm only where nature routinely deposits new nutrients. In the Nile delta, for example, the river's annual floods brought fresh soil from upstream and deposited it in the floodplain. Every year farmers there received an input of nitrogen, organic carbon, and other nutrients from outside the system. Other examples of this fertility solution come from the valleys of the Tigris and Euphrates rivers in Mesopotamia and, later, from the Yangtze and Hwang-ho rivers in China. A drawback to this method of nutrient maintenance was the restriction of cropland to a relatively narrow...