Modelling Sugarcane Growth in Response to Age, Insolation and Temperature.

Modelling sugarcane growth in response to age of cane, insolation and air temperature using first-order multiple regression analysis and a non-linear approach is investigated. Data are restricted to one variety from irrigated fields to eliminate the impact of varietal response and rainfall. Ten first-order models are investigated. The predictant is cane yield from 600 field tests. The predictors are cumulative values of insolation, maximum temperature and minimum temperature for 3, 6, 12, 18 months, or for each crop period derived from weather observations near the test plots. The low R-square values indicate that the selected predictor variables could not account for a substantial proportion of the variations of cane yield and the models have limited predictive values. The non-linear model is based on known functional relationships between growth and age, growth and insolation, and growth and maximum temperature. A mathematical expression that integrates the effect of age, insolation and maximum temperature is developed. The constant terms and coefficients of the equation are determined from the requirement that the model must produce results that are reasonable when compared with observed monthly elongation data. The non-linear model is validated and tested using another set of data. Following the successful validation of the model, simulated growth curves in response to age, insolation and maximum temperature are generated by computer. The three-dimensional presentation of the simulation curves provides a simple means for the analysis of the individual factors and their interactions on sugarcane growth. The proposed non-linear model may be useful in estimating potential growth and assessing growth performance. When combined with stalk population data, the model may be used to predict yields. The non-linear model shows that growth is not controlled by one factor alone, nor by a set of factors present in relative minima. Each factor has some definite influence on growth rate, depending upon the intensities of the other factors. However, only one limiting factor is required to cause the growth rate to be greatly reduced. Thus, when investigating sugarcane growth, the simultaneous effect of age, insolation and maximum temperature must be taken into consideration.