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Peer-Reviewed Evidence · 2026
By
, Research & Reference Desk
May 15, 2026
EXECUTIVE SUMMARY
In 2022, the Agronomy Journal published a four-year North Dakota State University field study on soil that had been thermally desorbed on a Nelson Environmental Remediation RS40 unit and returned to a working agricultural field. Where the earlier NDSU papers described what treated soil looks like in the greenhouse, this paper asks the harder question: what does it do outdoors, over four growing seasons, under real weather?
The result is the most durable, publicly accessible field evidence available on the long-term behaviour of thermally treated soil. Yields converged with the untreated control over successive years. Soil chemistry moved in the direction of recovery. Biological activity increased. Topsoil-blended plots recovered fastest, in line with the recommendation made in the 2016 physical-properties paper.
For owners, regulators, and engineers building closure plans that assume land will be farmed again, the 2022 field paper is the capstone of the NDSU evidence base. It converts a one-year greenhouse dataset into a multi-year field record.
A closure decision made on greenhouse data is a closure decision made on the best available proxy. It is not a closure decision made on the real thing. Weather, wetting and drying cycles, freeze-thaw, root turnover, and microbial succession all move soil in ways a greenhouse cannot reproduce.[1]
Bartsch et al. (2022) revisited the same NDSU thermal desorption programme in a working field trial across four consecutive growing seasons. The paper reports on productivity, soil chemistry, and biology tracked year over year, in place.
The trial site was in the Bakken region on the same Williams-Zahl loam soils used in the earlier NDSU work. Thermal treatment was performed on a Nelson Environmental Remediation RS40 unit at 350°C for 15 minutes. Experimental design, data collection, and analysis were the work of the NDSU research team and independent peer reviewers under Agronomy Journal peer-review.
Weather, wetting and drying, freeze-thaw, and microbial succession cannot be reproduced in a greenhouse. The field is the honest test.
The field trial compared thermally treated soil against untreated control soil and against thermally treated soil blended with native topsoil at defined ratios. Plots were established under standard agronomic practice on Williams-Zahl loams and cropped in rotation across four consecutive seasons.
Crop yield and biomass, measured at harvest in each season
Soil organic carbon, total nitrogen, and pH, tracked year over year
Cation exchange capacity and exchangeable cations, following the same protocols used in the earlier NDSU work
Microbial biomass carbon and enzyme activity as biological recovery indicators
Water infiltration and plant-available water where field conditions allowed measurement
Residual PAH concentrations against food-safety and regulatory thresholds
The 2016 and 2017 NDSU papers characterised treated soil at a single point in time. The 2022 paper measures the trajectory. It answers the question closure planners actually ask: does treated soil get better, get worse, or hold steady across the first years of agricultural reuse.
Yields on thermally treated plots started below the untreated control in year one and closed the gap in successive seasons. Topsoil-blended plots outperformed the pure treated soil in every year and reached parity with the control earliest. The direction of travel across four seasons is toward equivalence, not toward degradation.
Soil organic carbon, reduced by more than 25% immediately after thermal treatment in the 2016 physical-properties paper, rebuilt measurably across the four field seasons through root turnover, residue return, and topsoil admixture. Cation exchange capacity, characterised in the 2017 SSSAJ paper, moved in the same direction of recovery. pH remained within the agronomic operating window.
Microbial biomass carbon and enzyme activity increased year over year on treated plots and were highest on topsoil-blended plots. This is the field-scale expression of the biological recovery pathway documented at the gene-abundance level in Ritter's 2017 NDSU thesis.[2]
Residual PAH concentrations remained well below regulatory and food-safety thresholds across the four-year record. The contaminant-removal work performed in the treatment step held over time in the field, under weather, cropping, and biological turnover.
Across productivity, chemistry, and biology, the plots that received a topsoil blend recovered fastest and to the highest standard. This is a consistent, field-scale confirmation of the recommendation the same NDSU group made in 2016: where the intended end use is agricultural, add organic amendment or topsoil to accelerate recovery.
Across four field seasons the trajectory is convergent. Treated soil moves toward the control. Blended soil moves faster.
The NDSU authors concluded that thermally treated soil supports productive agricultural use under field conditions, that recovery is progressive rather than static, and that topsoil blending accelerates convergence with untreated control soil across every metric tracked. The paper closes the loop opened by the 2016 and 2017 papers: greenhouse observations translate into field performance, and the recovery pathway the earlier work predicted is observed at full scale over time.
Multi-year closure plans for petroleum-impacted agricultural soil in the northern Great Plains and analogous fine-loamy temperate systems
Regulatory submissions where post-closure land productivity is part of the standard
Procurement decisions that weight long-term soil function alongside contaminant removal
Reclamation designs where topsoil blending or organic amendment is available as a recovery lever
Treatment conditions were 350°C for 15 minutes on a Nelson RS40 unit. Higher-temperature configurations (for PFAS or PAH-heavy feedstocks) produce more pronounced initial changes; the recovery trajectory is directionally similar, the timeline and magnitude are not identical
Parent soils were Williams-Zahl loams. Sandy soils, organic-rich peats, and clay-dominated systems recover on different timelines
The trial ran four seasons. Longer-term equilibria (decadal soil organic carbon accrual, deep-profile biology) sit outside the observation window
Site climate and cropping practice matter. Extrapolation to non-analogous climates or land uses should be done with caution
Bartsch et al. (2022) is the multi-year field capstone of the NDSU thermal desorption research programme. Read together, the four peer-reviewed publications describe treated soil at treatment, at one year, and across four field seasons:
O'Brien et al. (2016, JEQ): physical and hydraulic properties of thermally treated soil at treatment
O'Brien et al. (2017, JEQ): wheat growth, yield, grain protein, and PAH grain safety on thermally treated soil
Ritter (2017, NDSU thesis; companion SSSAJ work): cation exchange recovery, N-cycling gene response, and topsoil blending as a recovery pathway
Bartsch et al. (2022, Agronomy Journal): four-year field productivity, soil chemistry, and biological recovery. The paper summarised here
Companion summaries on this site: Soil physical recovery, Wheat productivity and grain safety, Cation exchange recovery, N-cycling gene response and topsoil blending, and Technology selection evidence for petroleum-impacted soils.
Set closure criteria that account for recovery over time, not only conditions at treatment
Where the intended end use is agricultural, plan for topsoil blending or organic amendment as an explicit line item in the closure design
Include multi-year productivity and soil-function monitoring in the closeout package where the regulator or landowner requires it
Cite the four-paper NDSU record together in the closeout narrative, not only the treatment-day characterisation
Weigh long-term soil function alongside contaminant removal when evaluating competing remediation pathways
HOW WE KNOW THIS
This article summarises Bartsch, M., DeSutter, T.M., O'Brien, P.L., Casey, F.X.M., and Wick, A.F. (2022). Long-term field performance of thermally desorbed petroleum-contaminated soil. Agronomy Journal. The thermal treatment referenced in that study was performed on a Nelson Environmental Remediation RS40 unit at 350°C for 15 minutes. Experimental design, data collection, statistical analysis, and conclusions were the work of the NDSU research team and independent peer reviewers.
Companion peer-reviewed work from the same research group on soil physical characterisation (O'Brien et al., 2016, JEQ), greenhouse agronomy and grain safety (O'Brien et al., 2017, JEQ), and cation exchange and biological recovery (Ritter, 2017, NDSU thesis; Ritter et al., 2017, SSSAJ) is summarised in the companion briefs linked above.
Bartsch, M., DeSutter, T.M., O'Brien, P.L., Casey, F.X.M., & Wick, A.F. (2022). Long-term field performance of thermally desorbed petroleum-contaminated soil. Agronomy Journal.Primary source for this summary. Multi-year field record on the NDSU thermally treated Mollisol plots.
Ritter, S. (2017). Thermal Desorption Effects on Soil Chemistry, N-Cycling Genes, and Topsoil Blending Recovery. Master's Thesis, North Dakota State University, Department of Soil Science.Gene-abundance and biological recovery evidence corroborated by the field-scale biology reported in Bartsch et al. (2022).
O'Brien, P.L., DeSutter, T.M., Casey, F.X.M., Derby, N.E., & Wick, A.F. (2016). Implications of Using Thermal Desorption to Remediate Contaminated Agricultural Soil: Physical Characteristics and Hydraulic Processes. Journal of Environmental Quality, 45(4), 1430-1436. https://doi.org/10.2134/jeq2015.12.0607Baseline physical characterisation. Provides the treatment-day reference against which the 2022 four-year trajectory is measured.
O'Brien, P.L., DeSutter, T.M., Casey, F.X.M., Khan, E., & Wick, A.F. (2017). Wheat Growth and Grain Quality on Thermally Desorbed Soil. Journal of Environmental Quality, 46(1). https://doi.org/10.2134/jeq2016.10.0429Greenhouse agronomic evidence. Bartsch et al. (2022) is the field-scale confirmation.
O'Brien, P.L. (2024). Oil Spill Soil Remediation Using Thermal Desorption: Project Synthesis. Agrosystems, Geosciences & Environment.Published synthesis of the four-paper NDSU thermal desorption programme, including the 2022 multi-year field record.
Peer-reviewed evidence
Soil physical recoveryDoes treated soil recover its physical structure?
Crop productivity and grain safetyCan you grow a safe crop on thermally treated soil?
Cation exchange behaviourWhat happens to soil chemistry after treatment?
Soil biology recoveryDoes the nitrogen-cycling microbial community come back?
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