ESTIMATING SUGARCANE COMPOSITION USING TERNARY GROWTH RELATIONSHIPS

SUGARCANE stalk total sugar and moisture levels are strongly related. Sugarcane biomass ternary relationships observed over the course of the BSES Limited’s NIR program of work in the early 2000s allowed development of a method to estimate the levels of moisture, brix, pol, fibre and CCS present in cane. The method assumes that the composition of all healthy sugarcane is constrained to follow the same ternary growth curve and that the determination of a sample’s position on the growth curve can be used to estimate the levels of all ternary parameters (brix, fibre and moisture) and non-ternary parameters such as pol in juice and CCS. The method is equally effective in estimating sugarcane composition when applied to in-field whole stalk analysis or mill payment laboratory results. Both data sets show strong coefficients of determination (0.85–0.99) and standard errors of prediction of less than 6% over a wide range of sugarcane varieties, ratoon classes, geographic locations, farming practices and seasonal growing conditions. It is likely that the method will over-estimate sugar concentrations when applied to sugarcane that has deteriorated due to factors such as disease, pest damage, extreme water stress or delays after harvest; however this situation could be identified by a simple juice pH check. Further investigation is required into the effect of seasonal variation in the composition and concentration of the impurities in cane on the accuracy of the method. The generalised ternary growth method of estimating sugarcane composition has significant potential in providing reliable, cheap and rapid results for qualitative applications such as discrimination, ranking, maturity testing and product monitoring. This paper describes the development of the generalised ternary growth models for sugarcane and validation of the models using whole stalk and mill-delivered analysis results over several seasons.