Willard Lindsay and Understanding Fe and Zn Uptake by Plants.

Willard Lindsay was a colleague, friend and mentor to me and most of us who worked on soil chemistry and soil-plant relationships of nutrients and trace elements. His early work to move soil chemistry into physical chemical relationships of soil minerals was a very significant advance in soil chemistry. His early work with Hodgson and their students using computers to calculate equilibria helped many move in the direction of using computers in soil chemistry equilibrium calculations. Lindsay’s work helped establish the concept of soil mineral phases as the boundry condition for soil element solubility and phytoavailability. His book helped us all learn to think in terms of soil physical chemical equilibria.

I first met Willard at Beltsville when he stopped by to talk with John Brown and others about our research on his way to the ASA meeting in New York City in 1971. Lindsay and Halvorson were presenting two significant papers using chelating agents to estimate the activity of Zn²⁺ and Fe³⁺ requirement of plants. Our team at Beltsville had just used bathophenanthroline disulfonate to show that dicots had to reduce Fe³⁺ to Fe²⁺ before absorption of the Fe²⁺, while Willard was presenting a Fe³⁺ only model for corn. Their studies were important advances in understanding of chelators and microelement uptake by plants. And all this was before the discovery of phytosiderophores. Because they grew corn, they could not see what we had seen. And because Willard had a soil chemistry focus, he did not have a student volunteer to test these questions further for many years. I subsequently learned that he had graduate students write class papers showing why we had to be wrong about reduction of Fe³⁺ in uptake of Fe from Fe³⁺-chelates. In about 1980 I had the opportunity to visit Colorado State and present a seminar on the fullness of the "obligatory reduction" research. Our data from study of dicots were hard to ignore, but always subject to testing. So Willard asked Paul Schwab to investigate the redox aspects of Fe³⁺-chelates in the rhizosphere as his Ph.D. thesis, applying all of the principles of equilibrium chemistry that Lindsay had built up over the years. Yes, Schwab confirmed our findings, and helped confirm that grasses used a very different Fe³⁺only system for Fe uptake. All of our work now makes sense with current understandings of microelement uptake and chelation.

Dr. Lindsay was a great leader in the development of modern soil chemistry thinking, laying the foundation for consideration of equlibria with soil minerals, and how adsorption and chelation could buffer metal ion activity lower than that of solid phase minerals; and that kinetics could make equilibrium hard to find. Later discovery of new minerals formed in contaminated soils (such as the layered double hydroxides) depended on characterizing the change from baseline minerals and then application of new techniques. Willard Lindsay was a colleague, and mentor, who shared his ideas freely with many engaged in fundamental understandings of soil chemistry to all our benefit.