Pipeline study shows effects of soil compaction and crop yield at construction driveway


AMES, Iowa – An Iowa State University study examining the effects of soil disturbance and early remediation practices from the construction of the Dakota Access Pipeline shows significant soil compaction and gradual recovery in crop yields over five years.

The research, funded by the Dakota Access Pipeline (DAPL), aimed to investigate the structural effects of the underground pipeline on arable land. The pipeline transports crude oil over 1,172 miles from North Dakota to Patoka, Illinois, through South Dakota and approximately 347 miles in Iowa. The main objective of the study was to assess the extent of soil and crop disturbance in the approximately 150 foot driveway caused by clearing, topsoil removal and soil mixing, pipeline trenches and backfilling during the construction process.

Researchers also wanted to evaluate the effectiveness of government-mandated remediation requirements and a DAPL agricultural curb plan designed to minimize the impact on farmland. The Iowa Utility Code requires that pipeline projects remove the topsoil and work the exposed subsoil deeply before replacing the topsoil. Researchers continue to investigate the benefits of these practices, which can be costly.

Such field-based research to quantify soil properties and recovery in the years following pipeline installation on farmland is limited in the corn-soybean regions of the United States.

“Our results show that extensive soil disturbances from construction activities had a negative impact on the physical properties of the soil, which result from the mixing of topsoil and subsoil as well as soil compaction by heavy machinery,” said Mehari Tekeste, Assistant Professor for Agricultural and Biosystems Technology, Director of Ground machine dynamics laboratory in the state of Iowa and head of the project.

Tekeste worked with a team that included: Mark Hanna, retired agricultural engineer from Iowa State Extension; Robert Horton, Charles F. Curtiss Distinguished Professorship in Agricultural and Life Sciences in Agronomy; and Elnaz Ebrahimi, researcher in the field of agricultural and biosystems technology.

After the construction of the local pipeline was completed in 2016, researchers began studying the effects of construction and reclamation on a short section of the pipeline crossing an Iowa state research farm near Ames, Iowa. They monitored soil properties such as bulk density and chemical properties at different depths in three zones within the driveway and adjacent undisturbed fields. In 2017 and 2018, they analyzed yield data from corn and soybean plots that were grown on the newly reclaimed areas in the pipeline path under two tillage systems (direct and conventional tillage), and compared the yields with the harvests in the undisturbed fields similar soils. A peer-reviewed article in the magazine “Land use and management“Summarizes her first results.

“Overall, we found in the first two years that the construction was causing severe subsoil compaction and compromised physical soil structure that can inhibit root growth and reduce water ingress into the driveway,” said Horton, the project’s senior soil physicist . They also found changes in the available soil water and nutrients.

Although the compaction caused by heavy equipment was still visible two years after construction, deep tillage showed some benefit in relieving compaction.

The team found that the right of way crop yields were reduced by an average of 25% for soybeans and 15% for corn during the first and second harvest seasons compared to undisturbed fields.

“However, we are already seeing a gradual recovery in yields from the restored soybean corn rotation,” said Ebrahimi. “In addition, the results of our tillage comparisons indicate that the use of no-tillage improved maize production in the priority zones, especially under the unfavorable weather conditions of 2020.”

The researchers complete analyzes from the following years of the project. What you can say at this point is the compaction and the yields are starting to recover very slowly. Ebrahimi has increased the impact of soil compaction on crop yields over time Agricultural Production Systems Simulator (APSIM). A publication on their results is in progress.

“We want to continue this research – and especially more years of data on corn – and use it to recommend best management practices that can more effectively mitigate the impact of future pipeline installations on crop yields,” said Tekeste.

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