The concept of biological time for computing the switching points of a growth model for winter wheat

This paper deals with the prediction of the time points at which stem elongation and ear emergence of winter wheat are reached. The problem is analogous to that of predicting insect development stages. In entomological applications usually a temperature response function is used to calculate the development rate. Summation or integration of this development rate yields the biological time, which is a measure of the development state of the individuals. In this paper the same concept is applied to plant phenology. the general form of a plant model is discussed. The need to predict the starting time of certain growth stages is stressed. Afterwards, several methods of determining these time points are discussed, especially with respect to the predictive power. A comparison of the chosen non-linear approach with a linear temperature response shows the former to be superior. Based on these results a prediction of two growth stages of winter wheat was made.