Growing Degree Day Calculations

More thoughts from my Cropping Systems: An Integrated Approach coming at ya this Saturday evening. The topic of our class's discussion this week dealt with solving agronomic problems in field, focusing in on using Growing Degree Day (GDD) calculations to figure out when damage could have occurred, or to help stage other events in a crop's life.

Growing Degree Day calculations are important because heat units can give a very reliable prediction on how far along a crop is. For example, it takes about 75 GDDs for wheat to put on another full leaf. (A picture of the different growth stages of wheat can be seen below) 

Wheat growth stage chart from the University of Illinois

So how are GDD's calculated? If the information is available, the formula is: 

This formula changes for different crops. The base minimum temperature for wheat is 37F, and the minimum temperature for corn and soybeans is 50F. There is also a maximum; the final average, to be considered for GDD units, should not be greater than 86F for corn and soybeans and no greater than 77F for wheat.