Farm News reviews a lecture at the Iowa Academy of Sciences annual meeting in Ft. Dodge on farming techniques and their impacts on soil, runoff and water quality.
With more tile lines installed, more land opened for row crops and a 130 percent increase in rainfall over the past 130 years, Schilling said, Iowa’s soils no longer act as the sponge they once did before the steel plow arrived.
Iowa soils’ water-holding ability has been broken down so far, he said, the best Iowa can improve is getting back to its 1940s capability.
“With a 4-inch rain,” Schilling said, “you can expect 3 inches to run off” without any type of conservation practices.
And if corn demand continues to grow, he said, and more acres are converted to meet the demand, there will be even more discharges into the Mississippi River Basin.
Conservation practices are holding more soil in place, said Mary Skopec, a senior researcher with IDNR, but most erosion is occurring in streambeds, and nitrate leaching occurring through tile lines.
Skopec said Iowa needs more grasses planted to hold water back.
“That’s important,” she said, “because water carries the pollutants.”
From 1995 to 2008, Skopec said, nitrate flows in Iowa’s surface waters have multiplied six times. This is from more tile lines, but also more than a million acres returned to row cropping after coming out of conservation reserve.
“Only 10 percent of Iowa’s streams would test for safe levels of nitrates today,” Skopec said.
Schilling said urban areas also carry blame for the increased water contents in streams and erosion that occurs.
With more concrete and impervious surfaces from urban developments shedding rain and snow melt into streams, the water flows faster through the watersheds, although the flows don’t last as long, Schilling said.