FIGURE 6.1 Shift in farming practice in Iowa to row crops from earlier focus on sod crops around 1938 as a result of the Agricultural Adjustment Act. Source: Adapted from Jackson (2002).
For more than 60 years (1870 to the 1930s) Iowa farmers had maintained about 50 percent sod crop, but with passage of the Agricultural Adjustment Act of 1938 row crops began to dominate, with dramatic implications for flood resilience (Jackson, 2002). The traditional sod crops had dense root masses that absorbed rainfall without runoff and released it back to the atmosphere via transpiration and through underground flow into both shallow and deep aquifers (Jackson and Keeney, 2010). Because the crops were perennial, after harvest the root mass remained and was not tilled up, thus retaining and improving top soil. Knox (2006) describes the agricultural conversion of prairie and forest in the upper Mississippi Basin as the most important environmental change that influenced fluvial (river and stream) activity in this region in the past 10,000 years.
Even without impacts of climate change, farm practice (responding in part to policy) has significantly increased the flood potential in the Midwest. The overall effect of facilitating the drainage of millions of acres of farm fields through underground drains, combined with the shift from sod crops to row crops and the encroachment of many communities into the floodplain, was to reduce the resilience of cities and towns along Midwestern rivers by increasing the likelihood and intensity of flooding. To address this problem, Jackson and Keeney (2010) summarize a variety of proposed novel mitigation strategies including crop rotation, strip-cropping practice, crop mixing, as well as setting