W.G. Duncan – Father Of Crop Models

DR. DENNIS B. EGLI

LEXINGTON, KENTUCKY

Did you know that one of the ‘fathers’ of crop simulation modelling was a professor in the old Agronomy Department at the University of Kentucky?  I was reminded of this at a recent  seminar where the speaker used a crop simulation model to investigate the effects of planting date and variety maturity on soybean growth and yield. William G. Duncan, a friend and colleague from many years ago, was one of the first scientists to believe that it was possible to write a computer program that simulated the growth and production of yield by a grain crop. 

Many crop scientists at that time felt that crop growth was so complex and influenced by so many factors that it was impossible to construct a model that would mimic growth of a crop. Bill realized that the complexity of the system made it an ideal candidate for a simulation model. If scientists could describe the system, the computer could handle the complexity. Today that does not sound like such a rash proposition, but 60 some years ago it was an extraordinary idea, and it took an extraordinary person to give birth to such an idea. Bill Duncan was such an individual.

Bill was a native Kentuckian and, after obtaining a B.S. degree in chemical engineering from Purdue University in 1930, he farmed and operated a fertilizer business in Hopkinsville, Ky.  When he was 54 years old, he decided to sell his business and go back to school to study agronomy, receiving his Ph.D. degree from Purdue University in1959. He then joined the Agronomy faculty at the University of Kentucky.                  

Bill’s first model, developed with scientists at the University of California, Davis, (Duncan et al., 1967) was a simple model that calculated daily photosynthesis for a crop community as a function of leaf area, leaf display and solar radiation. This simple model was the precursor to today’s complex models that simulate growth throughout the crop’s life cycle and provide an estimate of yield. Modeling is now a very active research field with models available for all major grain crops.

There are at least three major benefits associated with the development and use of crop simulation models. First, as Bill put it – a model is “one way of putting what we know about the parts of the system back together to see how it functions as a whole” (Duncan, 1967). Crop scientists often study individual pieces of the system (photosynthesis, roots, seeds, nutrient or water availability etc.) without considering how their piece fits into the complete system. Models put the information on pieces back together to evaluate the contribution that each piece makes to the complete system.

Secondly, building a model requires a precise detailed description of the entire system. Developing this description often identifies important processes that haven’t been studied by crop physiologists. Model building stimulates research on these under-studied processes, so the interaction of modelers and experimentalists advances our overall understanding of crop growth. 

Finally, models make it possible to thoroughly study the interaction between the crop and its environment. Crop scientists know very well that they must evaluate varieties and management practices over a period of years and locations to sample a range in environments. It is never practically possible to run experiments long enough or at enough locations to thoroughly sample all possible environmental conditions. A three-year field experiment, for example, may never encounter a dry year, thereby providing a biased estimate of the treatment effect. Models make it possible to easily evaluate 30 years of weather data for many locations, providing a thorough evaluation of the treatment. Models may also make it possible to evaluate treatments that are impossible to test experimentally.

One of Bill’s first papers (Duncan, 1971) ( its publication was a ‘breakthrough’ of sorts because at that time journals were reluctant to publish model papers because they had no real data) illustrates the value of models. At that time, there was a lot of interest in whether vertical leaves would increase corn yield, a proposition that was very difficult to evaluate experimentally. Bill evaluated leaf angle with his model, where he could assign any angle to the leaves, and found that vertical leaves increased photosynthesis if the leaf area of the community was large enough; if it was too small, photosynthesis was reduced because vertical leaves reduced light interception.

Duncan had a tremendous effect on agronomy and crop physiology until he died in 1986. He made fundamental contributions to our understanding of how crop communities develop and produce yield, but his most important contribution was demonstrating that it was possible, with the help of a computer, to develop crop simulation models and thereby greatly enhance our ability to understand crop growth and its interaction with the environment. His contributions are even more impressive when we remember that he began his career at an age when many people are thinking of early retirement and that he received only token pay throughout his career. The legacy of William G. Duncan, the father of crop models, will always be with us. Remember – “Science is built with facts as a house is built with stones – but a collection of facts is no more science than a heap of stones is a house.” Jules Henri Poincare (1854 – 1912 ) French Philosopher of  Science and Mathematics.   ∆