Bob Sojka, Ph.D.
Retired January 2008
Background
R.E. Sojka earned a Ph.D. in Soil Science under Dr. L.H. Stolzy at the University of California at Riverside in 1974 investigating the relationship between physiological indicators of plant water stress and drought resistance in wheat. Dr. Sojka, working with Nobel laureate Dr. Norman Borlaug's research team at CIMMYT, was among the first to apply quantitative measurements of soil and plant water potentials to discrimination of drought resistance among wheat genotypes. His techniques have been used and adapted for drought breeding of wheat and other species around the world.
In other work at UC Riverside, Dr. Sojka was the first to observe and quantify a relationship between soil oxygen diffusion rate and leaf water vapor conductance. This provided the first quantitative explanation of plant stomatal response to soil oxygen. This finding eventually provided a dynamic criteria for determination of onset of flooding stress in a number of plants, for modelling leaf gas exchange of hypoxia-affected crops and for discriminating flooding resistance among species and cultivars.
Dr. Sojka was a postdoctoral research associate in the Agronomy Department of the University of Arkansas from 1974 to 1976. He applied plant water stress assessment techniques to improvement of irrigation management of soybean.
In 1976 Dr. Sojka became an assistant professor of soil science at North Dakota State University where he investigated crusting, plant emergence, and reduced tillage systems. At NDSU he published the first journal report of no-till sugarbeet production and taught the beginning course in soil science and a graduate level course on plant response to soil physical conditions.
In 1978 Dr. Sojka was hired by ARS as a soil scientist in Florence, South Carolina to investigate tillage and water stress problems in soybean production systems, including rotational crops and alternative crops. He established the feasibility of alternate double cropping systems with sunflower or canola, and helped identify the importance of subsoiling in conservation cropping systems on soils with subsoil rooting barriers. He and colleagues refuted the previous held notion of soil cooling as a barrier to no-till corn stand establishment for deep southern agriculture. He also showed the rotation-like effect of double cropping other species following corn and the benefit of shallow surface tillage following winter fallow for minimum-till corn. Working with colleagues they established the duration of the subsoiling effect on sandy southeastern soils and the importance of timing of the operation and combination with other conservation practices. He also expanded his original findings on the oxygen relationships of plants.
In 1986 Dr. Sojka moved to ARS's Northwest Irrigation and Soils Research Lab in Kimberly, ID. His current work concentrates on soil physical problems that affect crop responses and impact the environment. His work has focussed on conservation tillage systems, and since 1986 has paid special attention to solving problems associated with irrigation-induced erosion. Dr. Sojka developed several irrigated cropping practices to improve infiltration, reduce erosion and improve yield, market quality and value of several Northwest irrigated crops. Dr. Sojka has led a team effort that developed an improved rapid field technique and monitoring software for intensive characterization of furrow irrigation infiltration and erosion, greatly accelerating and broadening world research capabilities in this field of endeavor. He also led a team effort that resulted in the first field demonstration of the effect of furrow irrigation water quality on soil erodibility, and the essentiality of accounting for water quality in modelling furrow erosion dynamics.
Dr. Sojka has led a team effort to develop use of food grade polymers for the halting of irrigation-induced erosion. Polyacrylamide (PAM) dissolved in irrigation water has been shown to decrease furrow erosion 84-99% (avg. 94%) and increase infiltration 15% on silt loam soils, and more on finer textured soils. The reduction of sediment loss from fields also greatly reduces phosphorus, nitrogen, BOD, microorganism, weed seed, and pesticide pollution from irrigation return flows, while enhancing furrow irrigation management options. New workwith PAM has shown potential for numerous new and unforeseen soil and water management improvements. Dr. Sojka and colleagues are continuing research to expand the technology for use with sprinkler and drip irrigation.
Dr. Sojka is the author or coauthor of over 200 scientific papers. He is a Fellow of the American Society of Agronomy and Soil Science Society of America and a former Technical Editor of the soil and water conservation section of the Soil Science Society of America Journal. He is currently co-editing revision of the ASA monograph "Irrigation of Agricultural Crops". He is also a former Associate editor of Agronomy Journal and SSSAJ and has held office and served on numerous committees of several scientific societies, including ASA, SSSA, and Sigma Xi. He has been the recipient of numerous awards for his careerlong accomplishments.