Agricultural tile helps manage watershed

By Curt Zingula

By now we've all heard that Iowa's increasing annual rainfall puts development in the flood plain at greater risk of flooding. What's left to be heard is agriculture's role in watershed management.

Crop vegetation has changed dramatically in Iowa over the last 60 years. The biggest change was decreasing hay and pasture land by 8.8 million acres and adding 7.3 million acres of soybeans.

This 640 percent increase in soybean acres is an important factor for soil moisture. While perennials begin consuming considerable amounts of soil moisture in May and June, soybeans don't use very much soil moisture until July. May and June are two of the rainiest months of the year.

Despite this change, pulling the plug on planting soybeans would not be a good solution. This high-protein crop is easily stored, then shipped in large quantities to hungry nations.

The question then becomes: Will subsurface drainage tile (tubes) help or hinder the flooding associated with more rainfall and less vegetative water consumption?

Shedding light on that question is the Iowa Department of Natural Resources' flood committee member, Chuck Correll, who said, “We don't know if drainage tile increases flooding. On the one hand, we know that it adds to floodwater, but on the other hand we know that it allows the soil to absorb more water.” Correll sums up the situation nicely, but is anyone listening?

Farmers are incredulous that drainage tile critics already have handed down a kangaroo court conviction against tile without listening to our defense. That defense includes the fact that tile removes soil saturation and allows the soil to better absorb precipitation events.

This past winter, we were warned that deep snow cover and saturated soils were a recipe for severe spring flooding. However, when spring flooding was much less than anticipated, not a word was mentioned about tile working all winter long to remove saturation on the 40 percent of farmland it serves. Apparently people don't think of tile until they see an opportunity to find fault.

Farmers defend tile because they know that wet soils are susceptible to compaction by machinery and compaction reduces the soil's ability to absorb rainfall.

Farmers can tell you that tile prevents cold, wet soils and that allows us to perform less tillage to facilitate early growth of seedlings. Less tillage means burning less fossil fuel, releasing less carbon from the soil into the atmosphere, and of course, less erosion. In the case of no-till farming, soil organic matter is increased and that allows soil to retain more water.

Farmers also know that soils saturated for more than 36 hours experience denitrification, which involves anaerobic bacteria converting nitrogen fertilizer to nitrous oxide. Nitrous oxide dissipates into the atmosphere whereas a greenhouse

gas is 296 times more persistent than carbon dioxide.

Another testimony comes from the Iowa Department of Agriculture and Land Stewardship's Water Quality Director Dean Lemke, who asserts that, “Iowa needs more tile. ” Lemke, who is also a member of the Gulf Hypoxia Task Force, realizes that surplus water leaving a tile outlet is clear while surplus water running over the top of farm fields is brown with eroded sediment. Couple that thought with the knowledge that almost

75 percent of the DNR's 2008 list of Iowa's impaired water bodies were because of sediment pollution and we soon see the benefit of tile.

Once all the evidence is heard, the verdict will be that agricultural drainage tile benefits watershed management and the environment. Hopefully, protecting development in the flood plain will not lead to changes in agriculture that do more harm than good.

Curt Zingula of Marion is a fifth-generation farmer who serves as the Environmental Resource Chair and President of Linn County Farm Bureau. Comments:

czingula@aol.com