ABSTRACT
The systematic effects of historical agriculture on the physical landscape We must begin this chapter by reminding ourselves of the buffer or “cushion” that the virgin soils provided. While they were not “inexhaustible” as some thought, they were resilient and their depth, structure, infiltration capacity, and resistance to erosion gave the farmers an initial reprieve from serious erosion. How long was this reprieve? While we have no experimental studies to guide us on this, one to four decades seems reasonable based on the historical record. It would depend on the soil, slope, land use, and land management. Moreover, all of these variables varied widely and differed from place to place even on the same farm. In any case, 50 plus years of cultivation had to have had a deleterious effect on the excellent soil characteristics described in Chapter 1. With time, organic material, pedofaunal activity, and soil structure declined. Knox (2001) showed that organic carbon in a prairie soil had declined from about 5% to 6% in the virgin state to about 1.5% in a long-cultivated soil. The result of the foregoing changes was decreased structural integrity, decreased ability to resist erosion, increased bulk density, decreased infiltration capacity, and more overland flow; all the foregoing increased erosion. And with erosion of the topsoil, the process was accelerating. As discussed in the Introduction, the process involved the hydrologic transformation from the Hewlett Model to the Horton Model.
