Robert Horton
Office: 2543 AGRON
Phone: (515) 294-7843

B.S. (Agronomy), 1975, Texas A&M University
M.S. (Soil Science), 1977, Texas A&M University
Ph.D. (Soil Physics), 1981, New Mexico State University

Dr. Robert Horton is recognized nationally and internationally for his study of coupled heat and mass transfer in soil. His fundamental work on coupled heat and mass transfer in soil has greatly enhanced understanding of the following: climatology (the importance of surface energy partitioning); water quality (the impacts of soil water and chemical movement); agricultural production (the impact of the near surface environment on seed and root functions); ecosystem products and services (the impact of the near surface soil environment on microbial functions and gas exchange); and environmental investigations (thermal and mass flow methods for remediation of soil pollution). Dr. Horton leads a distinguished soil physics research and teaching program.


Dr. Hortonís groupís most significant contribution to science is the development and validation of theory describing coupled heat, water, and chemical transport processes in soil. They provide for the first time a general theory that describes the complex interaction of non-isothermal transfer processes in soil. The theory represents a major improvement over earlier coupled heat and water theory because chemical transport and its interaction with both heat and water are included. The validation experiments clearly show that water redistribution in response to thermal gradients is greatly affected by soil solution concentration. They have demonstrated that the theory can be used to accurately predict observed water and chemical redistribution in the presence of thermal gradients. Thermal gradients always exist in soil surface horizons. Therefore, this new theory is particularly useful for understanding surface and near surface processes such as evaporation, transport and fate of surface applied pesticide and shallow fertilizer bands. Thermal gradients also result from decomposition of buried organic wastes or by decay of buried radioactive waste. The theory provides a means of interpreting non-isothermal data, and it provides a means to predict soil temperature, soil water content, and soil solution concentration. Dr. Hortonís leading contributions in this area of soil research are reflected in the numerous national and international invitations he has received to lecture and teach on this topic. He has presented more than 100 invited talks including 70 international talks. He has been invited keynote speaker at two NSF-sponsored workshops on global heating effects on soil temperature. He was selected to present the prestigious Frontier Lecture at the American Geophysical Union national conference. He has received the Soil Science Research Award from the Soil Science Society of America for his research on coupled heat and water transfer in soil. The award is the highest research award offered by the society and recognizes the most outstanding fundamental soil science research over a sustained period.

Current Research Projects (2009)
Instrument Development

Dr. Hortonís group has not only made major advances in the science of coupled heat and mass flow, they have led development of sophisticated instruments that allow fellow scientists to measure these coupled phenomena. Dr. Horton and colleagues have developed and patented an instrument for determining hydraulic and chemical transport properties of field soil. The automated tension infiltrometer has been designed, constructed, tested, and is now available commercially. The tension infiltrometer is the only practical device available to soil scientists for field determination of hydraulic and chemical transport properties of surface soil. Dr. Horton and colleagues have used the infiltrometer to obtain spatial and temporal distributions of field hydraulic and chemical transport properties. Because it is now possible to measure these field properties, it is possible to apply stochastic preferential flow transport models in the field. The automated tension infiltrometer is currently used widely nationally and internationally.

Dr. Hortonís group has developed techniques for determining soil thermal properties in situ. Dr. Horton and colleagues have provided theoretical support and experimental validation of the dual probe heat pulse technique and the thermo-TDR probe for determining soil thermal properties and soil water content. Theory required to interpret the heat pulse data has been fully developed. The heat pulse method has been validated by showing that it provides accurate determination of thermal properties and water content for a set of standard materials. These instruments provide the only existing means of monitoring temperature, thermal properties, and water content of near surface soil, non-destructively and in situ. The thermo-TDR probe sends both electrical and heat pulses into soil. Dr. Horton and colleagues have shown that the device can be used to measure soil water fluxes, soil temperature, soil water content, soil solution concentration as inferred from electrical conductivity, and changes in soil bulk density. This instrument is being used nationally and internationally to measure heat and mass transfer within dynamic surface soil conditions.

Dr. Horton and colleagues have developed and tested a nitrogen fertilizer applicator that manages the soil around the fertilizer band in such a way as to minimize nitrate leaching from the band. The fertilizer applicator causes localized soil doming and compaction in order to redirect infiltrating water around the fertilizer band rather than through the fertilizer band. The soil management leads to reduction in leaching of nitrogen fertilizer and improved water quality. The applicator method and device are both patented.

Dr. Horton has consistently received competitive research and teaching grants throughout his career. As Principal Investigator his grant funds exceed $5 million. He has received federal grants from US Department of Agriculture, US Environmental Protection Agency, US Department of Energy,US Geological Survey, and US National Science Foundation.

Teaching and Advising

Dr. Horton has taught soil physics courses at Iowa State University since 1982. He has taught soil physics to more than 600 graduate students. He has co-authored a soil physics textbook published by Wiley. The book is a leading text for advanced soil physics courses nationally and internationally. Dr. Horton's outstanding record as a graduate teacher is clearly evidenced by the student course evaluations, which consistently rank his performance as Ďbeing among the top instructorsí at Iowa State University. Dr. Horton has served as a faculty advisor for 3 undergraduate research students, as major or co-major Professor for 15 Ph.D. students, and as major professor for 7 M.S. students. He has directed the research efforts of 14 Postdoctoral researchers. Four of his graduate students have received university awards for thesis research, another was awarded "best paper presented" at a Regional ASA Conference, and another the superior paper award from the American Society of Agricultural Engineers. Several of Dr. Hortonís former Ph.D. students and Post Docs are now faculty members performing excellent research and teaching students of their own at other institutions.

Dr. Horton served as a faculty member on the College of Agriculture Honors Program for 3 years. He was a member of the committee that completely revised curricula of all Agronomy Department undergraduate degree programs. He has taught short courses on coupled heat and mass transfer in soil nationally and abroad. Dr. Hortonhas presented educational seminars nationally and internationally on soil physics and water resources topics. He has made numerous presentations on soil water flow to gifted high school students as part of Iowa State University's recruitment effort. †In addition to giving lectures, he spends time with the undergraduate and graduate students to discuss current science and academic issues and future opportunities. †He works closely with students and encourages their personal development as well as their scientific development. He encourages students to become excellent scientists with balanced and wholesome lives. †He cares deeply for people and strives to serve them.

Dr. Horton also served as Chair of the Water Resources Graduate Major at Iowa State University for 7 years. He was active in recruiting and advising graduate students within the program. The program averaged 35 graduate students each semester during the 7 year time period. Under his leadership the water resources faculty and students voted to expand the Water Resources Program into an Environmental Sciences Program. †The new Environmental Science Program is now in place at Iowa State University.

Current Teaching Responsibilities
Agronomy 477/577, Soil Physics
Agronomy 578, Soil Physics Laboratory
Agronomy 677, Advanced Soil Physics

International Research and Teaching

Dr. Horton has traveled widely nationally and internationally. He has delivered more than 100 invited talks, including 70 international presentations. He has given presentations in Australia, Austria, Belgium, Canada, China, Egypt, Germany, Hungary, Israel, Japan, Lithuania, the Netherlands, Oman, Philippines, Russia, Slovakia, Spain, Switzerland, and throughout the USA.†He serves as a member of the Academic Advisory Committee for the Chinese Academy of Sciences National Laboratory of Soil Erosion and Dryland Farming at the Institute of Soil and Water Conservation. Through invitation Dr. Horton has worked with the worldís leading coupled soil and heat transfer scientists (Prof. Globus in Russia, Prof. Nassar in Egypt, Prof. Bachmann in Germany, Prof. Bristow in Australia, Prof. Noborio in Japan, and Profs. Shao, Ren, and Wang in China).


Dr. Horton combines premier research and teaching programs with a strong university ethic promoting publication recognition of students under his guidance. Dr. Horton has authored or co-authored 185 journal articles, 23 book chapters, 15 symposium papers and reports, and 1 book. He is named on three patents.

Recent Publications (2005-2009)
Professional Service

Dr. Horton reviews manuscripts, research proposals and programs related to soil science and water resources for many different public and private groups. He has served on editorial boards for Agronomy Journal, Soil Science, and Soil Science Society of America Journal. He served as a panel reviewer for CSREES water quality proposals. He served as a review team member for a CSREES review of the Soil Science Department at North Dakota State University, and on the review team for the ARS-National Soil Tilth Laboratory. He served on a team of experts who evaluated the research quality of the entire USDA-ARS Soils Program. He currently serves on the Technical Advisory Committee of BARD. Dr. Horton has provided extensive time as a reviewer domestic and foreign journal publications. Dr. Horton has served as reviewer for BARD, DOE, DOD, EPA, NSF, and USGS project proposals and reports. †Dr. Horton has served the Soil Science Society of America in many capacities, including being elected Chair of Division S-1 (Soil Physics).

Professional Recognition

Dr. Horton has repeatedly been recognized by his peers for his outstanding scientific contributions. He received the Soil Science Research Award from SSSA, the highest research award given by this organization. He received the Don and Betty Kirkham Soil Physics Award from SSSA, targeted at the most outstanding soil physics research accomplishments in the society. He is a Fellow of the American Society of Agronomy and of the Soil Science Society of America. ††He is a Distinguished Professor at Iowa State University, and an honorary professor at China Agricultural University.

Graduated Magna cum laude, Texas A&M University (1975)
Outstanding technical reviewer for the Soil and Water Division of the American Society of Agricultural Engineers (1989)
Raymond and Mary Baker Agronomic Excellence Award (1989)
Iowa State University Foundation Award for Mid-Career Achievement in Research (1990)
Elected Chairman of Soil Physics Division of the Soil Science Society of America (1993)
Fellow of the American Society of Agronomy (1993)
Fellow of the Soil Science Society of America (1994)
Appointed Chairman of the Soil Science Faculty Committee at ISU (1995-2002)
Appointed to Agronomy Department Headís Advisory Council (1995-2002)
Superior Paper Award of the American Society of Agricultural Engineers (1997)
Soil Science Research Award of the Soil Science Society of America (2001)
Don and Betty Kirkham Soil Physics Award of the Soil Science Society of America (2002)
CampbellLecturer, Washington State University (2004)
Frontiers of Hydrologic Sciences Lecturer, American Geophysics Union (2005)
Selected as Distinguished Professor, Iowa State University (2006)
Honorary Professor at China Agricultural University (2007)
Rossmann-Manatt Faculty Development Award, ISU (2009)