Dr. Robert Horton

People

About

Distinguished Professor

Robert Horton is a Distinguished Professor in the Agronomy Department at Iowa State University. His program addresses soil physical processes and soil physical properties, with a focus on coupled heat and mass transfer in soil. His fundamental work on coupled heat and mass transfer in soil has greatly enhanced understanding of the role of soils in the following topic areas: climatology (the importance of surface energy partitioning); water quality (the impacts of soil water and chemical movement); agricultural production (the impact of the soil environment on seed and root functions); ecosystem products and services (the impact of the soil environment on microbial function and gas exchange); and environmental investigations (thermal and mass flow methods for remediation of soil pollution). His singular contributions include a comprehensive theory of coupled heat, water and chemical transfer in soil, quantifying in situ unsaturated soil hydraulic conductivity and dynamic subsurface water evaporation, and devising and validating a method to control fertilizer nitrogen leaching. To reach these goals his program includes laboratory and field measurements, sensor development, theory development, and numerical modeling.

Awards
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 Head's 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)

Contact

rhorton@iastate.edu

Soil Physics

(515) 294-7843

2543 Agronomy 716 Farm House Ln

Ames

50011-1051

Education:

B.S., Agronomy, Texas A&M University, 1975

M.S., Soil Science, Texas A&M University, 1977

Ph.D., Soil Physics, New Mexico State University, 1981

Teaching:

Agron 477 & 577: Soil physics

Agron 578: Soil physics laboratory

Agron 677: Advanced soil physics

CV:

horton_cv_2019.pdf

Tags:

soil physics

Soil Water

Soil Heat Transfer

Projects

Determining soil water evaporation and subsurface evaporation zones

Evaporation from the soil largely determines water availability in terrestrial ecosystems and the partitioning of solar radiation between sensible and latent heat. It is key to hydrology and climate. The evaporation process is complex, involving movement and phase change of water, varying with depth and time. Following water inputs, evaporation occurs at the soil surface, controlled by atmospheric demand. As surface soil water is depleted, evaporation becomes soillimited and shifts below the surface; nonetheless it is generally viewed as a strictly surface process. As a result, measurement methods and understanding of these near-surface phenomena have lagged behind demand for accurate data. Much current research emphasizes large-scale areal estimates of soil moisture and temperature, but poor understanding of the soil water evaporation process causes low accuracy in water and energy balances. This poor understanding is largely due to our current inability to make the needed measurements. The purpose of the proposed research is to develop and test a new approach to measure evaporation within the soil. Recently developed sensors and concepts enable us to quantify sensible heat transferred into and out of mm-scale near-surface soil layers, as well as the change in sensible heat stored within each layer. Combined with conservation of energy, these measurements can locally quantify subsurface evaporation, showing the temporal patterns of in situ evaporation. Laboratory experiments will measure soil thermal properties, water content, and water flux under a combination of 2 energy regimes, 3 surface conditions, and 3 soils. Calculated evaporative loss via heat balance will be compared to evaporation measured by mass balance. In the field experiments, independent measurements of evaporation and transpiration will allow rigorous testing of heat balance estimates of transpiration and soil water evaporation.

Funding Organization:

National Science Foundation

Principal Investigator(s):

Tags:

Colloid-Mediated Transport of Hormones with Land-Applied Manure

Endocrine-disrupting hormones may enter the environment via land application of livestock manure. With respect to both livestock production and soils, Iowa is the prototype for agriculture in the Midwest. Our hypothesis is that the risk of hormone transport can be better understood by knowledge of the mechanisms of sorption, desorption, and transport of colloid-hormone complexes. Objectives are to (1) determine the rate, intensity, and capacity for adsorption and desorption of estrogens by colloidal components of cattle manure and three Iowa soils, (2) quantify the impact of physical and chemical variables that regulate colloid-mediated transport of estrogens in soils, and (3) quantify colloid-mediated pathways in the profile-scale dissipation of manure-associated estrogens. The research plan focuses on: (1) adsorption-desorption processes that determine how much of a land-applied hormone is transferred from manure to the aqueous phase or to the soil, (2) leaching of colloid-associated estrogens through aggregated, structured soils, and (3) transport of colloid-associated estrogens with runoff. This scale-integrated research will strengthen the development of transport models that are indispensable for assessing the environmental risk of hormones in land-applied livestock waste. The work proposed and will address issues where current knowledge is critically incomplete. At the project’s conclusion, we will have identified key mechanisms by which estrogens interact with colloidal organics in cattle manure and in soil. We will also have identified how those mechanisms can be incorporated into predictive models of hormone transport in or over soils.

Principal Investigator(s):

Dr. Robert Horton

Dr. Michael L Thompson

Tags:

Comparison of Biofuel Systems (COBS)

This project seeks to identify and develop cropping systems that produce large quantities of biofuel feedstocks while protecting soil and water resources and increasing biodiversity on the Iowa landscape. Treatments in the COBS experiment include a conventional corn-soybean cash grain system; continuous corn grown for grain and stover, with and without a winter cover crop; a mixture of perennial prairie plants fertilized for high biomass production; and a highly diverse, unfertilized mixture of prairie plants, which serves as a benchmark for understanding the functional characteristics of a native plant community. Our central premise is that cropping systems designed to produce large amounts of biomass, with high net energy return, can simultaneously create significant environmental benefits. Our working hypotheses are that (1) cover crops can reduce nutrient losses from corn production systems, (2) diverse mixtures of perennial plants can produce nearly as much biomass as conventionally managed corn, but with greater economic and energetic efficiency; and (3) diverse plant mixtures used for feedstock production can emit fewer pollutants to drainage water, sequester more carbon, and reduce greenhouse gas emissions relative to corn- and soybean-based cropping systems. We will compare systems by measuring plant productivity, resource use efficiency, nutrient dynamics, soil organic matter maintenance and production, carbon sequestration, CO2 emissions, and drainage water quantity and quality. Direct comparisons within a spectrum of cropping systems will lead to informed analyses of the advantages and disadvantages of each system.

Principal Investigator(s):

Dr. Robert Horton

Dr. Matt Liebman

Dr. Michael L Thompson

Tags:

People

Supervisor(s):

Dr. Kendall R Lamkey

Publications

Dr. Horton on Google Scholar

Selected publications

1) Woche, S. K., M.-O. Goebel, M. B. Kirkham, R. Horton, R. R. van der Ploeg, and J. Bachmann. 2005. Contact angle of soils as affected by depth, texture, and land management. European J. Soil Sci. 56: 239-251.

2) Ochsner, T. E., R. Horton, G. J. Kluitenberg, and Q. Wang. 2005. Evaluation of the heat pulse ratio technique for measuring soil water flux. Soil Sci. Soc. Am. J. 69: 757-765.

3) Helmke, M.F., W.W. Simpkins, and R. Horton. 2005. Fracture-controlled transport of nitrate and atrazine in four Iowa till units. J. Environ. Qual. 34: 227-236.

4) Ren, T., Z. Ju, Y. Gong, and R. Horton. 2005. Comparing heat-pulse and TDR soil water contents from thermo-TDR probes. Vadose Zone J. 4: 1080-1086.

5) Gaur, A., R. Horton, and D. B. Jaynes. 2006. Measured and predicted solute transport in a tile drained field. Soil Sci. Soc. Am. J. 70: 872-881.

6) Ochsner, T. E., T. J. Sauer, and R. Horton. 2006. Field tests of the soil heat flux plate method and some alternatives. Agron. J. 98:1005-1014.

7) Al-Jabri, S.A., J. Lee, A. Gaur, R. Horton and D.B. Jaynes. 2006. A dripper-TDR method for in situ determination of hydraulic conductivity and chemical transport properties of surface soils. Adv. Water Resour. 29: 239-249.

8) Zhou, J., J. L. Heitman, R. Horton, T. Ren, T. E. Ochsner, L. Prunty, R. P. Ewing and T. J. Sauer. 2006. Method for maintaining one-dimensional temperature gradients in unsaturated, closed soil cells. Soil Sci. Soc. Am. J. 70:1303-1309.

9) Bachmann, J., G. Arye, M. Deuer, S. K. Woche, R. Horton, K. H. Hartge, and Y. Chen. 2006. Universality of a surface tension – contact angle relation for hydrophobic soils of different texture. J. Plant Nutr. Soil Sci. 169: 745-753.

10) Ilsemann, J., R.R. van der Ploeg, R. Horton, and D. Hermsmeyer. 2006. A semi-analytical model for solute transport in layered dual-porosity media. J. Plant Nutr. Soil Sci. 169: 754-761.

11) Ochsner, T. E., T. J. Sauer, and R. Horton. 2007. Soil heat storage measurements in energy balance studies. Agron. J. 99:311-319.

12) Sauer, T. J., T. E. Ochsner, and R. Horton. 2007. Soil heat flux plates: heat flow distortion and thermal contact resistance. Agron. J. 99:304-310.

13) Lu, S., T. Ren, Y. Gong, and R. Horton. 2007. An improved model for predicting room temperature soil thermal conductivity versus water content. Soil Sci. Soc. Am. J. 71:8- 14.

14) Kluitenberg, G. J., T. E. Ochsner, and R. Horton. 2007. Improved analysis of heat pulse signals for soil water flux determination. Soil Sci. Soc. Am. J. 71:53-55.

15) Heitman, J.L., A. Gaur, R. Horton, D.B. Jaynes, and T.C. Kaspar. 2007. Field measurement of soil surface chemical transport properties for comparison of management zones. Soil Sci. Soc. Am. J. 71:529-536.

16) Gaur, A., D. B. Jaynes, R. Horton, and T. E. Ochsner. 2007. Surface and subsurface solute transport properties at row and inter-row positions. Soil Sci. 172:419-431.

17) Heitman, J.L., R. Horton, T. Ren, and T.E. Ochsner. 2007. An improved approach for measurement of coupled heat and water transfer in soil cells. Soil Sci. Soc. Am. J. 71:872-880.

18) Wang, Q. and R. Horton. 2007. Boundary layer theory description of solute transport in soil. Soil Sci. 172:835–841.

19) Ewing, R.P. and R. Horton. 2007. Thermal conductivity of a cubic lattice of spheres with capillary bridges. J. Phys. D: Applied Physics 40: 4959–4965.

20) Liu, G., B. Li, T. Ren, and R. Horton. 2007. Analytical solution of heat pulse method in a parallelepiped sample space. Soil Sci. Soc. Am. J. 71: 1607-1619.

21) Heitman, J.L., R. Horton, T. Ren, I.N. Nassar, and D. Davis. 2008. A test of coupled soil heat and water transfer prediction under transient boundary conditions. Soil Sci. Soc. Am. J. 72: 1197–1207.

22) Gieselman, H., J.L. Heitman, and R. Horton. 2008. Effect of a hydrophobic layer on the upward movement of water under freezing conditions. Soil Sci. 173:297-305.

23) Liu, X., T. Ren, and R. Horton. 2008. Determination of soil bulk density with thermo-TDR sensors. Soil Sci. Soc. Am. J. 72: 1000-1005.

24) Heitman, J.L., R. Horton, T.J. Sauer, and T.M. DeSutter. 2008. Sensible heat observations reveal soil-water evaporation dynamics. J. Hydromet. 9:165-171.

25) Liu, G., B. Li, T. Ren, R. Horton, and B. C. Si. 2008. Analytical solution of heat pulse method in a parallelepiped sample space with inclined needles. Soil Sci Soc Am J. 72: 1208–1216.

26) Gao, Z., R. Horton, L. Wang, H. Liu, and J. Wen. 2008. An improved force-restore method for soil temperature prediction. European J. Soil Sci. 59: 972–981.

27) Sauer, T.J., O.D. Akinyemi, P. Thery, J.L. Heitman, T.M. DeSutter, and R. Horton. 2008. Evaluation of a new, perforated heat flux plate design. International Com. Heat Mass Transfer 35:800–804.

28) Lu, S., T. Ren, and Y. Gong, and R. Horton. 2008. Evaluation of models for describing soil water retention curve from saturation to oven dryness. Soil Sci. Soc. Am. J. 72:1542–1546.

29) Heitman, J. L., X. Xiao, R. Horton, and T. J. Sauer. 2008. Sensible heat measurements indicating depth and magnitude of subsurface soil water evaporation. Water Resour. Res., 44, W00D05, DOI 10.1029/2008WR006961.

30) Gao, Z., D. H. Lenschow, R. Horton, M. Zhou, L. Wang, and J. Wen. 2008. Comparison of two soil temperature algorithms for a bare ground site on the Loess Plateau in China. J. Geophys. Res., 113, D18105, DOI 10.1029/2008JD010285.

31) Ju, Z., T. Ren, and R. Horton. 2008. Influences of dichlorodimethylsilane treatment on soil hydrophobicity, thermal conductivity, and electrical conductivity. Soil Sci. 173: 425– 432.

32) Huo, Z., M.A.Shao, and R. Horton. 2008. Impact of gully on soil moisture of shrubland in wind-water erosion crisscross region of the Loess Plateau. Pedosphere 18: 674–680.

33) Wei, X., M. Shao, R. Horton, and X. Han. 2009. Humic acid transport in water-saturated porous media. Environ. Model. Assess. DOI 10.1007/s10666-008-9186-y.

34) Hu, W., M. Shao, Q. Wang, J. Fan, and R. Horton. 2009. Temporal changes of soil hydraulic properties under different land uses. Geoderma 149:355-366.

35) Lu, S., Z. Ju, T. Ren, and R. Horton. 2009. A general approach to estimate soil water content from thermal inertia. Agric. Forest Meteorol., DOI 10.1016/j.agrformet.2009.05.011.

36) Fu, X., M. Shao, X. Wei, and R. Horton. 2009. Effects of two perennials, fallow and millet on distribution of phosphorous in soil and biomass on sloping loess land, China. Catena 77:200–206.

37) Wei, X., M. Shao, X. Fu, R. Horton, Y. Li, and X. Zhang. 2009. Distribution of soil organic C, N and P in three adjacent land use patterns in the northern Loess Plateau, China. Biogeochemistry DOI 10.1007/s10533-009-9350-8.

38) Davis, D.D., R. Horton, J.L. Heitman, and T. Ren. 2009. Wettability and hysteresis effects on water sorption in relatively dry soil. Soil Sci. Soc. Am. J. 73:1947–1951.

39) Wang, Q., R. Horton, and J. Fan. 2009. An analytical solution for one-dimensional water infiltration and redistribution in unsaturated soil. Pedosphere 19:104–110.

40) Li , Y., R. Horton, T. Ren and C. Chen. 2009. Investigating time scale effects on reference evapotranspiration from Epan data in north China. J. Appl. Meteor. Climatol., DOI: 10.1175/2009JAMC2130.1.

41) Andersen, D.S., R.T. Burns, L.B. Moody, M.J. Helmers, and R. Horton. 2009. Comparison of the Iowa State University – effluent limitation guidelines model with the soil-plantair-water model for evaluating containment basin performance. Transactions ASAE. (in press).

42) Fu, X., M. Shao, X. Wei, and R. Horton. 2009. Soil organic carbon and total nitrogen as affected by vegetation types in Northern Loess Plateau of China. Geoderma (in press).

43) Wei, X., M. Shao, X. Fu, and R. Horton. 2009. Changes in soil organic carbon and total nitrogen after 28 years grassland afforestation: Effects of tree species, slope position and soil order. Plant and Soil (in press).

44) Wang, L., R. Horton, and Z. Gao. 2009. Comparison of six algorithms to determine the soil apparent thermal diffusivity at a site in the Loess Plateau of China. Soil Sci. (in press).

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