- Soil structure and soil structure dynamics: Soil structure and soil functions; Interactions between soil biota and soil structure; Soil structure dynamics shaped by climatic forces, biological activity, and disturbance in the form of soil tillage and compaction by field traffic
- Soil compaction: Stress transmission in soil and tyre/track-soil contact properties (stress distribution, contact area); Soil mechanical behaviour; Impact of soil compaction on soil functions; Recovery of compacted soil; 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 tillage on physical functions and carbon and nutrient distribution and storage.
Current research activities include
Biophysical processes controlling recovery of compacted soil structure. Soil compaction due to agricultural operations is a serious threat to soil productivity and soil ecological functions in modern agriculture. Our knowledge regarding soil compaction recovery rates and recovery times is limited. A more definitive understanding of compacted soil recovery rates and times is not only needed for estimation of the real costs of compaction, but a more quantitative description of natural compaction recovery mechanisms and recovery pathways could also be used to develop site-specific soil management methods (or strategies) that accelerate compaction recovery. Together with colleagues from Agroscope (Switzerland) and the Swiss Federal Institute of Technology ETH (Switzerland) we launched a long-term field experiment for monitoring post-compaction evolution of soil structure, referred to as a soil structure observatory (SSO). The general aim of the SSO is to provide long-term observation data on soil structure evolution after disturbance in the form of compaction. This will allow quantification of compaction recovery rates and times, and therefore quantification of compaction costs. http://www.sso.ethz.ch/soil-structure-observatory-3.html
A web-based decision support tool for assessment of the risk of soil compaction due to agricultural field traffic: Soil compaction negatively affects key soil biophysical functions resulting in environmental (e.g. erosion, flooding, nutrient and pesticide leaching to groundwater) and agronomic problems (decreased root growth and plant development, with an associated reduction in crop yield). Together with colleagues from Aarhus University (Denmark) and the Bern University of Applied Sciences (Switzerland), we have developed a web-based decision support tool for assessment of the risk of soil compaction due to agricultural field traffic, called Terranimo®. This tool may help farmers and advisors in planning and making decisions about specific traffic situations in the field. Terranimo® incorporates recent developments in soil compaction modelling. We are currently refining the model (e.g., incorporating rubber-tracked vehicles) and preparing a Swedish version. www.terranimo.se
Stress-strain behaviour and stress transmission in structured arable soil: Our knowledge of how stress is transmitted in soil is limited. Together with colleagues from Aarhus University (Denmark) and INRA Montpellier (France) we combine approaches from classical soil mechanics and granular matter physics to better understand how forces are propagated in soil and how soil properties affect the way stresses are transmitted and soil is deformed. The research includes laboratory experiments, field measurements and modelling exercises.
Evaluation of soil improving cropping systems: Intensive agriculture jeopardizes soil quality. Soil improving cropping systems aim at maintaining or improving soil functions and at the same time ensuring high productivity. Such soil management systems are adapted to site and soil specific conditions, and may include reduced tillage, well-balanced crop rotation, cover crops, organic fertilizers, and good timing of field operations. Together with colleagues from Agroscope, the Swiss Federal Institute of Technology ETH and the Research Institute of Organic Agriculture (FiBL) we measure soil and crop properties and functions on farm fields under different soil managements (conventional farming, no-till, organic farming) and evaluate the suitability of soil management systems.
Tillage effects on soil organic carbon and phosphorus stratification and storage: The tillage system (e.g. conventional mouldboard ploughing, reduced tillage, or no-tillage) has strong impacts on soil properties and the depth-distribution of soil properties and functions. We use long-term field experiments and investigate the impacts of tillage or the absence of tillage (such as in no-till systems) on physical soil functions (e.g. gas transport functions) and carbon and nutrient distribution and storage in the soil profile.
- 2017 Professor of Soil Mechanics and Soil Management, Swedish University of Agricultural Sciences SLU Uppsala (Sweden)
- 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)
Ten selected recent publications:
Keller T., Colombi T., Ruiz S., Manalili M.P., Rek J., Stadelmann V., Wunderli H., Breitenstein D., Reiser R., Oberholzer H.-R., Schymanski S., Romero-Ruiz A., Linde N., Weisskopf P., Walter A. & Or D. 2017. Long-term soil structure observatory for monitoring post-compaction evolution of soil structure. Vadose Zone Journal, In press, doi: 10.2136/vzj2016.11.0118.
Guimarães R.M.L., Lamandé M., Munkholm L.J., Ball B.C. & Keller T. 2017. Opportunities and future directions for visual soil evaluation methods in soil structure research. Soil & Tillage Research, In press, http://dx.doi.org/10.1016/j.still.2017.01.016.
Colombi T., Braun S., Keller T. & Walter A. 2017. Artificial macropores attract crop roots and enhance plant productivity on compacted soils. Science of the Total Environment, 574, 1283-1293.
Martínez I., Chervet A., Weisskopf P., Sturny W.G., Rek J. & Keller T. 2016. Two decades of no-till in the Oberacker long-term field experiment: Part II. Soil porosity and gas transport parameters. Soil & Tillage Research, 163, 130-140.
Martínez I., Chervet A., Weisskopf P., Sturny W.G., Etana A., Stettler M., Forkman J. & Keller T. 2016. Two decades of no-till in the Oberacker long-term field experiment: Part I. Crop yield, soil organic carbon and nutrient distribution in the soil profile. Soil & Tillage Research, 163, 141-151.
Naderi-Boldaji M. & Keller T. 2016. The degree of soil compactness is highly correlated with the S-index. Soil & Tillage Research, 159, 41-46.
Keller T. & Arvidsson J. 2016. A model for prediction of vertical stress distribution near the soil surface below rubber-tracked undercarriage systems fitted on agricultural vehicles. Soil & Tillage Research, 155, 116-123.
Schjønning P., van den Akker J.J.H., Keller T., Greve M.H., Lamandé M., Simojoki A., Stettler M., Arvidsson J. & Breuning-Madsen H. 2015. Driver-Pressure-State-Impact-Response (DPSIR) analysis and risk assessment for soil compaction – a European perspective. Advances in Agronomy, 133, 183-237.
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., 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.