A simple model of unstressed sugarcane canopy development.

Abstract

Growth and water use of sugarcane are largely determined by the amount of radiation intercepted by the crop canopy. An accurate model of canopy development is therefore a prerequisite for useful predictions of growth and water use. Canopy development of three varieties grown in different seasons and localities were measured by the way they intercepted photosynthetically active radiation. An existing empirical model based on the Canegro simulation model was tested against data measured in an experiment at Pongola. This model calculates canopy cover as a function of thermal time and does not account for variety differences, row spacing or ratoon stage. An improved model was calibrated on the Pongola data set. Model parameters include base temperature, half canopy thermal time (both variety specific), a row spacing factor and a universal shape constant. Values for the base temperature were determined for the three varieties using an iterative process. The model was then validated against independent sets of data from La Mercy. Results show that the base temperature for all varieties was higher than previously documented values and that it varied between some varieties. NCo376 and N25 had a value of 16 o C, while N26 had a value of 17 o C. The new model predicted canopy cover for widely varying temperature regimes with a mean absolute error (MAE) of approximately 10 % compared to a MAE of 24 % for the existing model. Besides being used to support research in sugarcane, the model will assist management and planning of irrigation and weed control.