Environmental factors that influence the location of crop agriculture in the conterminous United States

This report presents and describes high-resolution geospatial data identifying the range of environmental conditions that influence the location of cropped agricultural lands in the conterminous United States. Also presented are estimates of the extent of land where environmental constraints limit agricultural production (marginal land) and the extents of land where modifications overcome environmental constraints. The report is the result of the compilation and manipulation of datasets from numerous sources; it consists of an explanatory text and a series of appendixes and associated tables that document the data sources and data-manipulation methods in detail.

Environmental factors that influence the extent of crop agriculture are terrain, climate, soil properties, and soil water. It is the combination of these four factors that allow specific crops to be grown in certain areas. Today, in order to maximize production, most of the cultivated croplands and grasslands for commercial agriculture are in areas where crops and livestock are well suited to local conditions. In the United States, cropland (row crops, closely sown crops (except hay), fruits, nuts, vegetables) occupies about 13 percent of the total land area. Grassland and rangeland occupy another 41 percent of the land area.

Most crops are grown on land with shallow slope where the temperature, precipitation, and soils are favorable. In areas that are too steep, wet, or dry, landscapes have been modified to allow cultivation. Some of the limitations of the environmental factors that determine the location of agriculture can be overcome through modifications, but others cannot. On a larger-than-field scale, agricultural modifications commonly influence water availability through irrigation and (or) drainage and soil fertility and (or) organic-matter content through amendments such as manure, commercial fertilizer and lime. In general, it is not feasible to modify the other environmental factors, soil texture, soil depth, soil mineralogy, temperature, and terrain at large scales.