FIGURE 3-1 Comparison of fertilizer (top) and pesticide (bottom) application rates for corn, soybean, and low-input high-diversity (LIHD; “biomass” in the figure) mixtures of native grassland perennials. Fertilizer and pesticide application rates are U.S. averages.

SOURCE: Tilman et al. (2006). Reprinted, with permission, from American Association for the Advancement of Science. © 2006 by the American Association for the Advancement in Science.

corn. The native grasses compare highly favorably to corn and soy for both fertilizers and pesticides, with order-of-magnitude lower application rates.

The impacts of these differences in inputs can be visualized nationally by comparing N inputs (such as fertilizer and manure) and the concentrations of nitrate in stream water (Figure 3-2, top). There are similar patterns for stream concentrations of atrazine, a major herbicide used in corn cultivation (Figure 3-2, bottom), although the environmental effects of pesticides in current use are difficult to decipher. Both of these maps show that regionally the highest stream concentrations occur where the rates of application are highest, and that these rates are highest in the U.S. “Corn Belt.” These stream flows of nitrate mainly represent application to corn, which is already the major source of total N loading to the Mississippi River.