use the radioactive tracers to which he had been introduced while in the military. To our knowledge Barber conducted the first field studies with radioactive tracers as part of his M.S. studies. After completing the M.S. in 1947, Barber applied for a two-year research fellowship and, upon its receipt, elected to study with C. E. Marshall of the University of Missouri. Professor Marshall, known as a rigorous mentor, was one of the best known and most accomplished soil chemists in the United States. By coming to the United States, Barber followed in the footsteps of many Canadians—such as Philip Low—who chose to study agriculture in the USA, thus enriching the lives of his colleagues in the United States. He completed studies for his Ph.D. and was immediately (in 1949) hired by Prof. J. B. Peterson, also a well-known soil physicist and chemist, who had left Iowa State University to become department head at Purdue. From the most humble of beginnings Barber rose to become one of the best known and respected soil scientists in the world.

At Purdue, Barber was given wide latitude in the choice of specialty to follow. With his strong background in physics and chemistry he elected to study the uptake of nutrients by plants. Until this time, plant nutrition had been studied in nutrient solutions and through field trials that were analyzed statistically. The introduction of statistics by Fisher and others provided agricultural science with a powerful tool, but a tool that had its limitations. In studying plant nutrition by combining knowledge of plant physiology, chemistry, physics, and mathematics, Barber pursued a line of research that was to go far beyond statistical techniques. With the aid of some 55 graduate students and 30 visiting scientists he pushed the empirical understandings further and further aside and replaced them with an increasingly theoretical understanding of the mechanisms of nutrient uptake by plants. Barber created an elegant and