Evaluation of deep tillage remediation in a construction easement on soil compaction and crop yield

Pipeline installations have been reported to cause soil compaction. Recently, an energy transfer pipeline was installed across the upper Midwest of the United State that affected agricultural land throughout the state of Iowa. Long-term research is needed to determine the best management practices to remediate subsoil compaction, and restore topsoil productivity to allow for maximum crop yield recovery. A five-year research study has been undergoing to evaluate the response of crop productivity and soil physical properties to subsoiling treatments in the construction Right-of-Way [ROW] on a farm field at Iowa State University. The specific objectives for this study are to: (i) investigate the effects of subsoiling depths as remediation practices of soil bulk density and crop yield, and (ii) determine if the crop yield is affected by soil disturbance from pipeline installation. The experiment was set up in a Randomized Complete Block Design to investigate the subsoiling depths in three ROW zones designated by construction activities, and two adjacent unaffected zones. Soil bulk density samples were taken to quantify the soil compaction that occurred after heavy trafficking and pipeline installation, and proceeding subsoiling treatment. Crop yields (corn and soybean) were monitored in the subsequent years. Observed soil bulk density and crop yield values were statistically analyzed (P-value 0.05) with SAS statistical software to evaluate the effects of subsoiling treatments. The soil bulk densities were found to be the highest in the ROW, indicating subsoil compaction from construction activities. The highest soil bulk density value (1.74 g/cm3) was found in the most heavily trafficked zone post-pipeline installation. Soil bulk density in the lightly trafficked zone had the highest soil bulk density value (1.74 g/cm3) after subsoil treatments were applied, suggesting subsoil compaction was persistent regardless. Subsoiling treatment depth did not show statistical differences in the ROW for soil bulk density. Overall, the average soil bulk density observed within the ROW was significantly larger than those in adjacent unaffected areas. Soybean yield in the year following pipeline installation had significant deficits in the ROW in comparison to the unaffected areas. The lowest observed crop yield was the heavily trafficked ROW zone (2.77 MT/ha), therefore showed the greatest deficit of -35.5%. However, soybean yields were not found statistically different between the two subsoiling depths. The corn yield in the following year also had significant deficits in the ROW verses the adjacent unaffected areas. The lowest observation of corn yield was again in the ROW heavy traffic zone (11.45 MT/ha). However, the maximum deficit for corn yield was only -23.3%, giving the impression that the crop yield is recovering from the soil disturbance. Again, no statistical difference was found in the subsoiling treatments for corn yield. The first three years of this study showed significant differences in soil compaction and crop yield between the ROW and unaffected areas. Both soil compaction measurements and crop yield showed no signs of differences between subsoiling depths within the ROW. Differences in both years of crop yield indicated that the topsoil disturbance from pipeline installation did have a significant impact on the yield when compared to undisturbed areas. However, the different construction activities within the ROW did not prove to be distinct from one another when comparing crop yield. This however needs to be further investigated to determine the long-term effects of crop yield response to soil disturbance—including other soil biological, chemical and physical factors that affect yield