Thomas Keller

Research interests

• Soil structure and soil structure dynamics: Interactions between soil biota, soil structure and soil functions; Soil structure dynamics shaped by climatic forces, biological activity, and disturbance in the form of soil tillage and compaction by field traffic
• Plant-soil interaction: Influence of soil physical stress on root architecture and anatomy and plant development; Carbon inputs to soil by plants; Mechanisms of soil structure formation driven by plant roots.
• Earthworm burrowing: Influence of soil conditions, land use and climate on burrowing rates and energy costs of burrowing.
• Soil compaction: Stress transmission in soil and tyre/track-soil contact properties; 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 and draught requirement.
• Soil management: Impacts of soil management on soil properties and functions, including questions related to soil health and crop yield stability.

Current research activities and on-going projects of our group include

Soil structure dynamics is a research focus of our group, and most projects relate to how soil structure is shaped by soil management (including unintentional negative impacts such as compaction), plant roots, soil fauna, and climate. Our research interests include soil structure recovery following compaction, aiming at better quantifying mechanisms and rates of soil structure recovery.

Plant-soil interactions.  On-going research aims to better understand how root architecture and anatomical traits are influenced by soil physical stress (high mechanical resistance, lack of oxygen) and whether the plant response is reversible or irreversible. In one project we study carbon inputs, and water and nutrient uptake of mixed cultivar systems and test whether such cropping systems are more drought resistant than single cultivar systems. Projects are funded by Formas, Lantmännen, KSLA, and Novo Nordisk Fonden.

Earthworm burrowing.  We currently have two PhD projects in our group, aiming to quantify earthworm burrowing rates and energy costs of burrowing as a function of soil conditions (soil mechanical resistance, soil moisture, soil temperature), land use and climate. Projects are funded by Formas, KSLA, and the Faculty of Natural Resources and Agricultural Sciences.

Soil compaction.  On-going projects aim at better predicting where (e.g. in Europe, within Sweden or across the fields of a farm) and when (temporal dynamics during the year) we have high compaction risks, how this will change in a future climate, and how we can minimize compaction risks by adapting soil management to site-specific conditions. We update our decision support tool www.terranimo.se as we gain new knowledge. Projects are funded by SLF, Formas, and EU Horizon 2020 through ICT-AGRI-FOOD and EJP SOIL.

Considering soil functions in spatial planning.  Soil is a finite resource, hence avoiding soil degradation and protecting soil functions is of high importance in any land use. We run a couple of projects concerned with minimising negative impacts on soils and their functions in road planning and construction, and measures and mass movement required for slope stability and landslide hazard minimization. Projects are funded by the Conference of European Directors of Roads and the Swedish Geotechnical Institute.

Soil management.  We investigate relationships between soil and crop management (crop rotation, cover crops, soil tillage, fertilization, structure liming), soil properties (or soil health indicators) and soil functions including crop yield stability in on-farm studies and long-term field experiments. Projects are funded by SLF, the Swedish Board of Agriculture and EU Horizon 2020 through EJP SOIL.

Carbon input to soils.  We recently started a project where we investigate how we can increase carbon inputs into soils by plant roots by means of crop rotations, cover crops and mixed cultivar systems, and how enhanced carbon inputs trigger other soil processes with potentially positive (synergies) and negative (trade-offs) effects, focussing on crop productivity, nitrogen cycling, and soil hydraulic and mechanical functions. The project is funded by Formas within the call on carbon sequestration as a climate measure in agricultural lands.

• 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)

Tschanz P., Vogel S., Walter A., Keller T. & Albrecht M. 2022. Nesting of ground-nesting bees in arable fields is not associated with tillage system per se, but with distance to field edge, crop cover, soil and landscape context. Journal of Applied Ecology, doi: 10.1111/1365-2664.14317. 

Arrázola-Vásquez E., Larsbo M., Capowiez Y., Taylor A., Sandin M., Iseskog D. & Keller T. 2022. Earthworm burrowing modes and rates depend on earthworm species and soil mechanical resistance. Applied Soil Ecology, 178, 104568.

Sjulgård H., Colombi T. & Keller T. 2022. Spatiotemporal patterns of crop diversity reveal potential for diversification in Swedish agriculture. Agriculture, Ecosystems & Environment, 336, 108046.

Keller T. & Or D. 2022. Farm vehicles approaching weights of sauropods exceed safe mechanical limits for soil functioning. Proceedings of the National Academy of Sciences of the United States of America, 119 (21), e2117699119, doi: 10.1073/pnas.2117699119.

Parvin N., Coucheney E., Gren I.-M., Andersson H., Elofsson K., Jarvis N.‡ & Keller T.‡ 2022. On the relationships between the size of agricultural machinery, soil quality and net revenues for farmers and society. Soil Security, 6, 100044.

Sjulgård H., Iseskog D., Kirchgessner N., Bengough A.G., Keller T. & Colombi T., 2021. Reversible and irreversible root phenotypic plasticity under fluctuating soil physical conditions. Environmental and Experimental Botany, 188, 104494.

Keller T., Colombi T., Ruiz, S., Schymanski, S., Weisskopf P., Koestel J., Sommer M., Stadelmann V., Breitenstein D., Kirchgessner N., Walter A. & Or D. 2021. Soil structure recovery following compaction – short-term evolution of soil physical properties in a loamy soil. Soil Science Society of America Journal, 85, 1002-1020.

Or D., Keller T. & Schlesinger W.H. 2021. Natural and managed soil structure: on the fragile scaffolding for soil functioning. Soil & Tillage Research, 208, 104912.

Torres C.L., Keller T., Lima R.P., Tormena C.A., Lima H., Giarola N.F.B. 2021. Impacts of soil texture and crop species on permanent wilting of plants. Geoderma, 384, 114798.

Williams H., Colombi T. & Keller T. 2020. The influence of soil management on soil health: an on-farm study in southern Sweden. Geoderma, 360, 114010, doi: 10.1016/j.geoderma.2019.114010.

ten Damme L., Stettler M., Pinet F., Vervaet P., Keller T., Munkholm L.J. & Lamandé M. 2020. Construction of modern wide, low-inflation pressure tyres per se does not affect soil stress. Soil & Tillage Research, 204, 104708.

Keller T., Sandin M., Colombi T., Horn R. & Or D. 2019. Historical increase in agricultural machinery weights enhanced soil stress levels and adversely affected soil functioning. Soil & Tillage Research, 194, 104293, doi: 10.1016/j.still.2019.104293.

Colombi T., Hermann A.M., Vallenback P. & Keller T. 2019. Cortical cell diameter is key to energy costs of root growth in wheat. Plant Physiology, 180, 2049-2060, doi: https://doi.org/10.1104/pp.19.00262.

Colombi T. & Keller T. 2019. Developing strategies to recover crop productivity after soil compaction – A plant eco-physiological perspective. Soil & Tillage Research, 191, 156-161, doi: 10.1016/j.still.2019.04.008.