When the Dakota Access Pipeline route crossed an ag research area at Iowa State in 2016, it provided a unique opportunity to study the effects of pipeline construction, especially soil compaction caused by heavy machinery, on crop yields.
The Iowa State team found yields in the 150-foot pipeline right-of-way were reduced by an average of 25% for soybeans and 15% for corn in the first two crop seasons after construction, compared to undisturbed fields.
“Recovering crop yields is a slow process,” said Mehari Tekeste, an assistant professor in the Iowa State Department of Agricultural and Biosystems Engineering.
In addition to compaction, mixing of the topsoil and subsoil also had negative effects.
Working with Tekeste were Mark Hanna, retired Iowa State Extension agricultural engineer; Robert Horton, an agronomy professor; and Elnaz Ebrahimi, research scientist in agricultural and biosystems engineering.
The Iowa Utility Code requires pipeline projects to remove topsoil and apply deep tillage to exposed subsoil before replacing the topsoil. Photo by Whitney Baxter / Iowa State University
The findings are off particular interest now as two major pipeline projects are in the works in Iowa. The Summit Carbon Solutions Midwest Carbon Express would head northwest out of Iowa to western North Dakota, connecting 31 ethanol plants in five states. Navigator CO2’s Heartland Greenway Pipeline would go east into Illinois. Both would be taking carbon dioxide from ethanol plants for underground storage.
The route of the Midwest Carbon Express
In the case of Dakota Access, it was built to take oil from western North Dakota to Illinois.
One of the main differences that Tekeste sees between the Dakota Access and the Summit project is the size of the pipeline.
The Dakota Access pipe was 30 inches in diameter. Jimmy Powell, chief operations officer for Summit Carbon Solutions, said it plans no bigger than a 16 inch diameter pipe. In Minnesota, off the main branch of the pipeline, the pipe will be 8 inches in diameter, Powell said.
“The magnitude of trenching would probably not be the same,” Tekeste said of the smaller pipe.
The other main take away for Tekeste: “You cannot do reclamation without deep tillage.”
But he said there was a not a significant difference in yield recovery between areas where the deep tillage was 12 inches deep versus where it was 18 inches deep.
But below 20 inches deep, he said there was “root limiting” compaction from pipeline construction.
Powell said with the smaller pipe, the weight of the heavy machinery should be less, creating less compaction.
Powell said the Iowa State findings would be included in its Agricultural Impact Mitigation Plan, a requirement that the Iowa Utilities Board has added since the Dakota Access construction.
Summit also will be required to take soil samples every 500 feet to more accurately detect where the topsoil ends and subsoil begins and “not just relying on color,” Powell said.
Also included in the plan would be to do deep tillage in the subsoil after it is returned to the pipeline trench and before the topsoil is returned.
Powell said it is hoped that the deep tillage will help reduce the yield loss found in the Iowa State study.
Nevertheless, Summit is offering to pay farmers for 100% yield loss in the first year after the pipeline is built. Construction is expected to be in 2023 if all goes as planned. Summit would compensate farmers for 80% yield lost in the second and 60% in the third year after construction.
“We think the offer is more than fair,” Powell said.
The Iowa study showed that there was slightly more rapid yield recovery in areas where no-till farming was used.
Tekeste said he would like to continue the research and look at other practices may speed yield recovery, such as the use of cover crops.
