Erosion of farmland in Iowa could be leaving $1 billion worth of crop in the fields.

“As you drive across the countryside in Iowa, and you look at the topsoil … we see a lot of yellow,” said Rick Cruse, an agronomy professor at Iowa State University. “That’s because we’ve eroded the top soil.”

Cruse said the soil that has been exposed does not carry the same nutrient value or water-holding capacity as the black topsoil that dominates Iowa’s farmland, meaning it could produce less crop.

“If you have some of this nice black stuff, you can work marvels,” he said.

He said as the top soil thins, the yield of the land suffers as well. He said he calculated the dollar amount based on how much topsoil yields in terms of bushel of crop, relative to its depth and the price of the crop per bushel — and it’s a conservative estimate.

“We lose production capacity as top soil thins,” Cruse said. He noted that the ability to grow different types of crops changes as the topsoil thins.

Cruse said erosion across the state occurs at a rate of 5.2 tons per acre per year. He said if this same rate has been true for the 150 years Iowa land has been farmed, then top soil has eroded by as much as 7 inches.

One state official said there are several ways to prevent soil erosion.

Jim Gillespie, the division director of the state Bureau of Soil Conservation, said he wouldn’t have any way to know the exact dollar amount of how much is being lost due to erosion.

He said responsible tilling practices and cover cropping could help prevent wind and rain erosion.

“We want to keep it in place now and well into the future,” Gillespie said. “Our soil is very productive; if not, we wouldn’t lead the nation in crop production.”

Tiffin area farmer Steve Swenka said he employs many of these practices on his farm and also uses grassy water ways to catch runoff.

“Every good farmer is naturally concerned with conservation. Farmers today are very proactive to minimize erosion,” Swenka said. “It’s all about staying one step ahead of Mother Nature.”

In addition to those practices, Cruse, Brian Gelder, an associate scientist at Iowa State University, and other researchers are working on the Iowa Daily Erosion Project II, an update to the previous version that will allow officials to identify areas at risk of erosion and measure erosion at a daily rate more accurately than ever statewide.

Cruse said users will be able to measure erosion in one-half kilometer by one-half kilometer squares.

Gelder said the new system will take into account the entire process of tilling, planting, growing, and harvesting crops and will also use precipitation measurements on five-minute increments instead of 15 minutes.

The project will also consider the steepness of a hill and the length of the slopes. He said it will also account for temperature and residue left behind by the last season’s crops.

“The new model is simulating the whole process,” Gelder said.

He said the new system will be ready in the coming months.