Cost effectiveness of conservation practices in controlling water erosion in Iowa

Iowa has severe water-induced soil erosion and associated water quality concerns because of intense agricultural activities. The objective of this study was to determine the effectiveness and economic benefits of selected conservation practices in sediment reduction by water erosion in major soil areas of Iowa. One farm was selected to represent the typical soil and slope gradient in each of the eight Major Land Resource Areas (MLRAs) in Iowa. Three tillage systems [no-tillage (NT), strip-tillage (ST), and chisel-plow tillage (CP)] and three conservation structures [grassed waterways (GS), grass filter strips (FS), and terrace systems (TS)] were investigated under a corn-soybean rotation using the Water Erosion Prediction Project (WEPP) model. Corn yields of some areas were statistically lower under NT than under CP while soybeans showed little response to tillage operations. Estimated annual sediment yield with the chisel plow system ranged between 0.7 and 56.9Tha⁻¹. The WEPP simulations showed that NT and ST systems were very effective in reducing soil erosion and sediment yield by approximately 90% in highly erodible lands compared to the CP system. The combination of conservation tillage with soil erosion control structures further mitigated soil loss and was more effective in areas with high water erosion potential than in the flat areas. The costs and benefits analysis indicated that the simulated conservation practices could increase the net benefit by up to $300ha⁻¹ compared to the CP system after the cost of eroded soil was taken into account. The findings suggest that NT and conservation structures have greater environmental and economic benefits in areas with high water erosion potential. The use of no-till in flat areas such as central Iowa may not be economically favorable because of the limited benefit in reducing soil water erosion. Overall, the study findings suggest that structural conservation practices coupled with tillage systems effectiveness were area-specific based on the soil and landscape in each area.