- Stress transmission in soil and tyre/track-soil contact properties (stress distribution, contact area); Soil mechanical behaviour; Soil compaction modelling and : Combining the above mentioned aspects into simulation models; Development of decision support tools for risk assessment of soil compaction.
- Soil tillage: Impacts of soil conditions and tillage implement properties on soil breakup during tillage (soil structure produced by tillage) and draught requirement.
- Soil management: Impacts of soil management and soil compaction on soil pore architecture and soil functions, water and gas transport processes, and crop growth.
Current research activities include
Biophysical processes controlling restoration of compacted soil structure. Togehter with colleagues from Agroscope (CH) and the Swiss Federal Institute of Technoligy ETH (CH) we launched a long-term soil structure observatory (SSO) to quantify post-compaction structural restoration at time scales of years to a decade. The SSO was designed to monitor key biophysical mechanisms that affect structure restoration of compacted soil, including effects of root and earthworm bioturbation, and abiotic wetting-drying, shrink-swell and freeze-thaw cycles. SSO field observations will be supplemented by quantitative modelling and laboratory studies of key soil structure processes.
Impact of long-term subsoil compaction on soil functions: This is investigated in the inter-nordic project POSEIDON which focuses on effects of subsoil compaction on soil pore functioning, water flow, and solute and gas transport processes.
Development of a web-based decision support tool for assessment of the risk of soil compaction due to agricultural field traffic: The tool is developed in collaboration with researchers from Aarhus University (DK) and the Bern University of Applied Sciences (CH), and incorporates recent developments in soil compaction modelling.
Tillage effects on soil organic carbon and phosphorus stratification and storage in Swedish soils (together with Ararso Etana).
Stress-strain behaviour and stress transmission in structured arable soil. This is investigated together with researchers from Aarhus University (DK) and INRA Montpellier (F).
Boards, committees, etc.
Chairman, Working Group on Subsoil Compaction of the International Soil Tillage Research Organization (ISTRO )
Convenor and host, International Exploratory Workshop on Soil Compaction Modelling, Zürich (CH), 2010
Co-organizer, NJF Seminar on Soil Compaction, Helsinki (FIN), 2012; ISTRO Visual Soil Examination and Evaluation (VSEE) and Subsoil Compaction joint meeting “Soil structural quality of tropical soils”, Maringá, PR (BRA), 2014
2011 Associate Professor (Swedish: Docent) in Soil Management, Swedish University of Agricultural Sciences SLU Uppsala (Sweden)
2005 Ph.D. in Soil Science (Soil Mechanics), SLU Uppsala (Sweden)
2000 Rural Engineer (Dipl. Kultur-Ing. ETH), Swiss Federal Institute of Technology ETH Zürich (Switzerland)
Selected publications (45 papers in peer-reviewed journals; h-index: 14; citations >500)
Keller T., Lamandé M., Arvidsson J., Berli M., Ruiz S., Schjønning P. & Selvadurai A.P.S. 2014. Transmission of vertical soil stress under agricultural tyres: Comparing measurements with simulations. Soil & Tillage Research, 140, 106-117.
Keller T., Carizzoni M., Berisso F.E., Stettler M. & Lamandé M. 2013. Measuring the dynamic soil response during repeated wheeling using seismic methods. Vadose Zone Journal, 12(3), doi:10.2136/vzj2013.01.0033.
Berisso F.E., Schjønning P., Lamandé M., Weisskopf P., Stettler M. & Keller T. 2013. Effects of the stress field induced by a running tyre on the soil pore system. Soil & Tillage Research, 131, 36-46.
Keller T., Lamandé M., Peth S., Berli M., Delenne J.-Y., Baumgarten W., Rabbel W., Radjaï F., Rajchenbach J., Selvadurai A.P.S. & Or D. 2013. An interdisciplinary approach towards improved understanding of soil deformation during compaction. Soil & Tillage Research, 128, 61-80.
Naderi-Boldaji M., Alimardani R., Sharifi A., Hemmat A., Keyhani A., Loonstra E., Weisskopf P., Stettler M. & Keller T. 2013. Use of a triple-sensor fusion system for on-the-go measurement of soil compaction. Soil & Tillage Research, 128, 44-53.
Etana A., Larsbo M., Keller T., Arvidsson J., Schjønning P., Forkman J. & Jarvis N. 2013. Persistent subsoil compaction and its effects on preferential flow patterns in a loamy till soil. Geoderma, 192, 430-436.
Keller T., Arvidsson J., Schjønning P., Lamandé M., Stettler M. & Weisskopf P. 2012. In situ subsoil stress-strain behavior in relation to soil precompression stress. Soil Science, 177(8), 490-497.
Keller T., Sutter J.A., Nissen K. & Rydberg T. 2012. Using field measurement of saturated soil hydraulic conductivity to detect low yielding zones in three Swedish fields. Soil & Tillage Research, 124, 68-77.
Keller T., Lamandé M., Schjønning P. & Dexter A.R. 2011. Analysis of soil compression curves from uniaxial confined compression tests. Geoderma, 163, 13-23.
Keller T. & Lamandé M. 2010. Challenges in the development of analytical soil compaction models. Soil & Tillage Research 111(1), 54-64.
Keller T. & Håkansson I. 2010. Estimation of reference bulk density from soil particle size distribution and soil organic matter content. Geoderma 154(3-4), 398-406.
Keller T., Défossez P., Weisskopf P., Arvidsson J. & Richard G. 2007. SoilFlex: A model for prediction of soil stresses and soil compaction due to agricultural field traffic including a synthesis of analytical approaches. Soil & Tillage Research 93(2), 391-411.
Keller T., Arvidsson J. & Dexter A.R. 2007. Soil structures produced by tillage as affected by soil water content and the physical quality of soil. Soil & Tillage Research 92(1-2), 45-52.
Keller T. 2005. A model for prediction of the contact area and the distribution of vertical stress below agricultural tyres from readily-available tyre parameters. Biosystems Engineering 92(1), 85-96.