Philip A. Helmke
Professor

Soil chemistry

• Contact Information
• Program Affiliations
• Education
• Teaching and Research
• Selected Publications
• Awards and Honors

Contact Information

Phone: 608-263-4947
Fax: 608-265-2595
Email: pahelmke@wisc.edu
Office: 172A Soil Science

Program Affiliations

Education

• B.S. Chemistry and Physics, 1964, University of Wisconsin-Stevens Point
• Ph.D. Analytical Chemistry, 1971, University of Wisconsin-Madison

Teaching and Research

Our research group studies the concentrations and behavior of the chemical elements in the various phases and components of the soil-water-plant system. Our objective is to understand the reaction pathways of the elements in this important biogeochemical system. We apply this knowledge to problems affecting the bioavailability and uptake of elements by plants and to the behavior of elements added to soils from recycled wastes and contaminants. Trace metals and phosphorus are emphasized.

Our group uses several analytical techniques to unravel the chemical complexity of the soil-water-plant system. These include neutron activation analysis, x-ray fluorescence analysis, inductively coupled plasma-mass spectroscopy, inductively coupled plasma-emission spectroscopy, and atomic absorption spectrophotometry for precise determination of element concentrations; high performance liquid chromatography for identification of soluble compounds; and radioactive and stable isotope tracer techniques to measure lability of elements and to trace their reaction pathways. Researchers in our group become expert analysts of environmental samples by using this wide variety of analytical techniques.

Central to the understanding of trace metal behavior in soil systems is experimental information on the chemical forms of the elements in solution. We have developed and applied an analytical technique utilizing ion exchange membranes and the principles of Donnan equilibrium to measure the concentrations of the free, hydrated cationic forms of the elements in solution under indigenous equilibrium conditions. This information is coupled with data on the concentrations of organic acids and other complexing agents from chromatographic techniques to study the bioavailability of trace elements to plants.

Current projects include studies of the ion exchange and solubility phenomena that control the concentrations of trace metals in soil solutions. In addition to laboratory studies of natural soil-water systems, we synthesize soil minerals that contain trace metals as impurities and determine their solubility and other properties. Laboratory and greenhouse experiments are used to study the chemical mechanisms that plants use to modify the rhizosphere to enhance the bioavailability and uptake of elements. Of special interest is the effect of root exudates from the proteoid roots of lupines and their effects on enzymes and soil humic substances that increase the uptake of soil phosphorus and other elements.

Publications

• Brown, D.J., K. McSweeney, and P.A. Helmke. 2004. Statistical, geochemical, and morphological analyses of stone line formation in Uganda. Geomorph. 62(3-4):217-237.
• Brown, D.J., P.A. Helmke, and M.K. Clayton. 2003. Robust geochemical indices for redox and weathering on a granite laterite landscape in central Uganda. Geochim. Cosmochim. Acta 67:2711-2723.
• Yoon, S.H., P.A. Helmke, J.E. Amonette, and W.F. Bleam. 2002. X-ray adsorption and magnetic studies of Ln 3+ sorbed on pristine and phosphate-modified boehmite surfaces. Langmuir 18:10128-10136.
• Szulczewski, M.D., P.A. Helmke, P.A., and W.F. Bleam. 2001. XANES spectroscopy studies of Cr(VI) reduction by thiols in organosulfur compounds and humic substances. Environ. Sci. Tech. 35:1134-1141.
• Helmke, P.A. 2000. The chemical composition of soils. p. B3-B24. In M.E. Sumner (ed.). Handbook of Soil Science. CRC Press, Boca Raton, FL.
• Xia, K., U.L. Skyllberg, W.F. Bleam, P.R. Bloom, E.A. Nater, and P.A. Helmke. 1999. X-ray absorption spectroscopic evidence for the complexation of Hg(II) by reduced sulfur in soil humic substances. Environ. Sci. Technol. 33:257-261.
• Helmke, P.A., 1999. Chemistry of cadmium in soil solution. p. 39-64. In M.J. McLaughlin and B.R. Singh (eds.) Cadmium in Soils and Plants. Kluwer Academic Publishers, Dordrecht, Netherlands.
• Xia, K., R.W. Taylor, W.F. Bleam, and P.A. Helmke. 1998. The distribution of Cu(II) on boehmite and silica surfaces: correlating EPR signal loss with the effective Bohr magneton number of sorbed ions. J. Colloid Interface Sci. 199:77-82.
• Salam, A.K., and P.A. Helmke. 1998. The pH dependence of free ionic activities and total dissolved concentrations of copper and cadmium in soil solution. Geoderma. 83:281-291.
• Xia, K., F. Weesner, W.F. Bleam, P.R. Bloom, U.L. Skyllberg, and P.A. Helmke. 1998. XANES studies of oxidation states of sulfur in aquatic and soil humic substances. Soil Sci. Soc. Am. J. 62:1240-1246.
• Helmke, P.A., A.K. Salam, and Y. Li. 1997. Measurement and behavior of indigenous levels of the free hydrated cations of Cu, Zn, and Cd in the soil-water system. Proc. of Third International Conf. on Biogeochemistry of Trace Elements. May 1995. Paris, France.
• Szulczewski, M.D., P.A. Helmke, and W.F. Bleam. 1997. Comparison of XANES analyses and extractions to determine chromium speciation in contaminated soils. Environ. Sci. Technol. 31:2954-2959.
• Bland, W.L., P.A. Helmke, and J.M. Baker. 1997. High-resolution snow-water equivalent measurement by gamma-ray spectroscopy. Agric. Forest. Meteorol. 83:27-35.
• Xia, K., W.F. Bleam, and P.A. Helmke. 1997. Studies of the nature of the binding sites of first row transition elements bound to aquatic and soil humic substances using X-ray absorption spectroscopy. Geochim. Cosmochim. Acta. 61:2223-2235.
• Xia, K., W.F. Bleam, and P.A. Helmke. 1997. Studies of the nature of Cu 2+ and Pb 2+ binding sites in soil humic substances using X-ray absorption spectroscopy. Geochim. Cosmochim. Acta. 61:2211-2221.
• Helmke, P.A., and R. Naidu. 1996. Fate of contaminants in the soil environment: Metal contaminants. p. 69-93. In R. Naidu et al. (ed.) Contaminants in the soil environment in the Australasia-Pacific Region. 18-23 February 1996. Adelaide, Australia. Kluwer Academic Publishers. Dordrecht, The Netherlands.
• Braum, S.M., and P.A. Helmke. 1995. White lupine utilizes soil phosphorus that is unavailable to soybean. Plant Soil 176:95-100.
• Fitch, A., and P.A. Helmke. 1989. Donnan equilibrium/graphite furnace atomic absorption estimates of soil extract complexation capacities. Anal. Chem. 61:1295-1298.
• Helmke, P.A., and R.B. Corey. 1989. Physical and chemical considerations for the development of Lunar derived soils. p. 193-212. In D.W. Ming and D.L. Henninger (eds.) Lunar derived soils for the growth of plants. ASA, Madison, WI.

Awards and Honors