Indicator : Erosion of cropland

Rationale: Preventing or minimizing erosion is critical to the long-term productivity of the state's soil.

Year 1982 14.4% 1987 11.8% 1992 10.1% 1997 8.7%

Data source: U.S. Department of Agriculture

Year 1982 37.9% 1987 42.8% 1992 41.1% 1997 38.9%

Data source: U.S. Department of Agriculture

About this indicator: Water erosion improved steadily while wind erosion rose and then fell between 1982 and 1997. Soils have what is called a tolerance level, which is the average tons per acre per year that cropland can lose and still maintain high levels of productivity indefinitely.

The percentage of cropland estimated to be eroding above tolerance levels due to water declined from 14 percent to 9 percent between 1982 and 1997. By contrast, estimated erosion due to wind rose from 38 percent in 1982 to 43 percent in 1987, then dropped back to 39 percent in 1997. Erosion not only wastes fertile topsoil but also causes water pollution. Eroded soil carries nutrients and pesticides into lakes and streams, clouding and polluting the water. Other types of soil loss not counted in this indicator include stream bank and gully erosion and urban erosion.

For comparison: In 1997, an estimated 17 percent of U.S. cropland had water erosion above tolerance levels compared to 9 percent in Minnesota. For the nation, 13 percent of cropland was estimated to have unacceptable wind erosion, compared to 39 percent in Minnesota. Neighboring states, such as Wisconsin and Iowa, had higher water erosion estimates than Minnesota's 17 percent in 1997 (Wisconsin with 22 percent and Iowa with 27 percent). However, both Iowa and Wisconsin had vastly lower wind erosion estimates, at 2.1 percent and 1.6 percent respectively, compared to Minnesota's 39 percent. The higher water erosion estimates in Wisconsin and Iowa reflect heavier summer rainfall and heavier reliance on row crops such as corn and soybeans. Minnesota's higher wind erosion estimates reflect large expanses of flat fields in the Red River Valley. National and state goals are to have no cropland with soil erosion above tolerance levels.

Things to think about: Losing topsoil is like spending an inheritance. Soils take a long time to form. The weathering of minerals and the accumulation of stable humus (organic matter) that make up fertile topsoil can take 3 to 15 years for an inch of young soil, to hundreds or thousands of years for more mature soils. Even tolerance levels of erosion can cause significant water pollution and net loss of soil.

Erosion potential is most affected by changes in crops and tillage practices. In 1997, as in 1982, cultivated cropland was responsible for at least 96 percent of the total soil loss while making up less than 75 percent of the acres on which the loss was estimated. Sustainable agricultural practices, including crop rotation and low- or no-till preparation of land for planting, are often advocated as a means of reducing erosion, preserving productivity and protecting water quality.

Technical notes: The data for this indicator covers both cultivated and non-cultivated cropland. The latter is often grass-covered and less prone to erosion. Erosion estimates are based on soil type, crops grown, tillage practices and typical climate conditions.

Sources:

• Minnesota Natural Resources Conservation Service, USDA, www.mn.nrcs.usda.gov
• Northwest Area Foundation, A Better Row to Hoe: The Economic, Environmental, and Social Impact of Sustainable Agriculture, December 1994, www.nwaf.org

Related indicators:

• Growth in gross state product
• Timber harvest
• Toxic chemicals
• Water quality in lakes and rivers
• Nitrate in ground water
• Wildlife habitat
• Changes in land use
• Parkland and open space