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Ryan Stewart

Associate Professor
Ryan Stewart
185 Ag Quad Lane
241 Smyth Hall
Blacksburg, Virginia


I am an Associate Professor in the School of Plant and Environmental Sciences. My research focuses on identifying and quantifying interactions between water, soil, and plant communities. This effort includes a combination of field work, laboratory analysis, and modeling. I foster active collaboration across disciplines, working on topics which span soil science, ecology, engineering, agriculture, and urban systems.


  • Soil Hydrology
  • Water Resources Management


  • Ph.D. Water Resources Engineering (Soil Science Minor), Oregon State University, 2013
  • M.S.  Water Resources Engineering, Oregon State University, 2010
  • B. S. Mechanical Engineering, Cal Poly – San Luis Obispo, 2002

Research Interests

  • Assessing soil health based on physical, chemical and biological properties
  • Evaluating effects of agricultural practices on soil characteristics and biogeochemical cycling 
  • Developing novel instrumentation to monitor environmental processes
  • Quantifying hydrological processes in structured and macroporous soils
  • Measuring and interpreting soil physical and hydraulic properties 
  • Creating soil hydrologic models using analytical and numerical solutions
  • Assessing and modeling hydrological processes within vegetated filter strips
  • Understanding soil controls on exchange of water vapor and greenhouse gases
  • Measuring solute transport (e.g., pesticides and nutrients) through variably-saturated soils
  • Understanding wildfire effects on soil properties and watershed hydrology in humid forests

Undergraduate Courses

Soil physical and mechanical properties and the physical processes controlling soil water retention and flow in agronomic and natural settings. Grain size distribution, weight-volume relationships, specific surface, electrical charge density, consistency, stress, compaction, rainfall runoff, water retention, steady/non-steady water flow in saturated/unsaturated soil, infiltration, bare soil evaporation, and soil water balance. Pre: (3114, 3124) or (GEOS 3614, GEOS 3624). (3H,3C)

Physical processes that control the fate of pollutants in our land, air, and water resources. Types and sources of pollutants, physical processes in the soil-water-atmosphere continuum controlling the dispersion and deposition of pollutants, the movement of pollutants, including radionuclides, by surface and subsurface water flow in soils, and physics of disturbed soils. I Pre: 3114, PHYS 2206, MATH 2016. (3H,3C)

Graduate Course

Physical concepts of hydrological processes that affect age, origin, and flowpaths of water from hillslope to watershed scales.  Analysis of current and historical research methods.  Hydrological science as an interdisciplinary topic. Pre: Graduate standing (3H, 3C)

Associate Professor | August 2020 – present
School of Plant and Environmental Sciences
Virginia Tech

Assistant Professor | December 2013 – August 2020
School of Plant and Environmental Sciences
Virginia Tech

  • 2016 Editors’ Citation for Excellence in Refereeing - Reviews of Geophysics, December 2016     
  • Virginia Tech Scholar of the Week - Awarded by the Virginia Tech Office of the Vice President for Research, March 2016
  • Wade Rain Irrigation Scholarship - Oregon State University Department of Biological & Ecological Engineering, May 2013
  • Ralph M. Lunde Memorial Award - Oregon State University Department of Biological & Ecological Engineering, May 2011
  • Myron G. Cropsey Award - Oregon State University Department of Biological & Ecological Engineer, May 2010


  1. Di Prima, S., M. Castellini, M. R. Abou Najm, R. D. Stewart, R. Angulo-Jaramillo, t. Winiarski, L. Lassabatere. Experimental Assessment of a New Comprehensive Model for Single Ring Infiltration Data. Journal of Hydrology.
  2. *Radolinski, J., *J. Wu, K. Xia, W. C. Hession, and R. D. Stewart. 2019. Plants mediate precipitation-driven transport of a neonicotinoid pesticide. Chemosphere.
  3. Stewart, R. D. 2019. A generalized analytical solution for preferential infiltration and wetting. Vadose Zone Journal
  4. *Shulte, M. L., D. L. McLaughlin, F. C. Wurster, J. M. Varner, R. D. Stewart, W. M. Aust, C. N. Jones and *B. Gile. 2019. Short- And Long-Term Hydrologic Controls on Smoldering Fire in Wetland Soils. International Journal of Wildland Fire.
  5. *Gyawali, A. J., and R. D. Stewart. 2019. An Improved Method for Quantifying Soil Aggregate Stability. Soil Science Society of America Journal
  6. Stewart, R. D., J. Jian, *A. J. Gyawali, W. E. Thomason, B. D. Badgley, M. S. Reiter, et al. 2018. What We Talk about When We Talk about Soil Health. Agricultural & Environmental Letters, 3(1).
  7. Stewart, R. D. and M. R. Abou Najm. 2018. A comprehensive model for single ring infiltration 2: Estimating field-saturated hydraulic conductivity. Soil Science Society of America Journal, 82(3), 558-567.
  8. *McCourty, M., *A. J. Gyawali, and R. D. Stewart. 2018. Of macropores and tillage: influence of biomass incorporation on cover crop decomposition and soil respiration. Soil Use and Management, 34, 101-110.
  9. *Radolinski, J., *J. Wu, K. Xia, and R. D. Stewart. 2018. Transport of a neonicotinoid pesticide, thiamethoxam, from artificial seed coatings. Science of the Total Environment, 618, 561-568.
  10. Stewart, R. D., Z. Liu, D. E. Rupp, C. W. Higgins and J. S. Selker. 2015. A new instrument to measure plot-scale runoff. Geoscientific Instrumentation, Methods and Data Systems, 4(1), 57-64. 
  11. Stewart, R. D., M. R. Abou Najm, D. E. Rupp, J. W. Lane, H. C. Uribe, J. L. Arumí, and J. S. Selker. 2014. Hillslope runoff thresholds in shrink-swell clay soils. Hydrological Processes, 29(4): 557-571.