Report suggests topsoil loss is being understated

A recent report from a conservation group suggests that Iowa loses more topsoil than previously thought. The Environmental Working Group (EWG) released the report, ?Losing Ground,? earlier this week.

In 2007, the United States Department of Agriculture released a study which found that the state lost an average of 5.2 tons of topsoil per acre per year, just above what it termed the ?tolerable loss? rate of 5 tons per acre. The EWG?s report argues that the USDA?s estimates are too low because it doesn?t consider the effect of extreme rainfall that causes most erosion.

Topsoil is the layer of soil closest to the surface, which contains most of the plant life on land. Mahdi Al-Kaisi is a soil management specialist in Iowa State University?s Agronomy Department. He said topsoil can range in depth from a few inches to several feet.

Topsoil is necessary for growing crops because it contains the organic matter plants live on. Unfortunately, the all-important topsoil can wash away. This occurs when water flows across the top of the soil and takes the minerals with it downstream.

Tilling the soil makes it vulnerable to being washed away in a hard rain. Al-Kaisi said that is one reason farmers practice ?no-till? which means leaving the soil nearly undisturbed.

There are other ways to reduce topsoil erosion in addition to ?no-till.? One is to channel the flow of water in the field along shallow, grass waterways. The bed of the waterway is seeded with grass or legumes, which slow the water and trap the nutrients in the soil, rather than allowing them to flow with the current.

Al-Kaisi said the grass slows the minerals and gives them more time to infiltrate into the soil. He said the waterways are an essential part of land management and need to be reseeded regularly.

Grass waterways also serve to trap chemicals used in fertilizers, pesticides and herbicides. The failure to prevent the flow of these chemicals to the Mississippi River has produced the ?Dead Zone? in the Gulf of Mexico, an area the size of New Jersey where very little aquatic life can live.

?We have to spend significant resources to clean up these waters,? said Al-Kaisi. ?This has both an economic and a health impact.?

Another way to prevent soil erosion and fertilizer runoff is to plant bushes and trees along a stream. This vegetation is known as a riparian buffer strip. Al-Kaisi recommends installing a riparian buffer strip, especially if the farmer has livestock.

?It?s good to designate a crossing area for the livestock so they don?t cross different areas and increase the damage to the whole bank system,? said Al-Kaisi.

The federal government has programs that will pay for some of these soil conservation practices. The Conservation Reserve Program (CRP) pays farmers to convert highly erodible cropland to grasslands, shade trees, and other kinds of buffer strips.