The Sun's Work in a Cornfield.

After extensive field experiments, we developed SPAM, a comprehensive mathematical model that simulates energy and material exchange in the plantair layer at the earth's interface. The model is based upon the conservation of energy, where the sun is the driving force. Our understanding and deficiencies were gauged initially by testing model predictions against actual experience with a relatively simple system-a cornfield. Climatic predictions are physically and biologically good enough for many applications, but they reveal inadequacies in our understanding of the fluid dynamics of airflow within the plant stand. Our present inability to measure or predict the degree of wetness of the soil surface hampers correct prediction of evaporation. Probably the most difficult problem to resolve is that of predicting how stomates open and close under drought stress, thus affecting both evaporation and photosynthesis in leaves. Along with resolution of these problems, the basic framework of the model can be adapted to more complex systems in nature, where variability is much greater than in an agricultural crop. The model in its present form can be used, with caution, as a powerful tool to help man order his priorities of plant community traits for whatever outcome he desires, be it food production, nature and water conservation, climate modification, or esthetic enjoyment.