Prediction of sugarcane sucrose content with high resolution, hyperspectral leaf reflectance measurements

Remote sensing for crop maturity parameters may offer sugarcane producers a method to develop harvest schedules that maximize sucrose production. Several tests were conducted to determine if leaf reflectance measurements could be used to predict theoretically recoverable sugar (TRS) levels (crop maturity) prior to harvest. Leaf samples were collected from multi-variety first-ratoon (FR) sugarcane maturity studies in 2005 at three sample dates and from the plant-cane (PC) and first-ratoon (FR) sugarcane maturity studies throughout the 2006 September through December harvest season. Sugarcane juice was analyzed for its Brix, and sucrose content to predict TRS and leaf reflectance measurements were taken using a dual input, fiber optic spectrometer. Discriminant analysis showed that leaf reflectance was effective at predicting TRS in 56-79% of the cases if cultivars were combined using resubstitution and in 36-54 % of the cases using cross validation. If the cultivars were considered separately then 99-100% of the cases could be correctly classified using resubstitution and 60-100% of the cases using cross validation. Regression analyses between leaf reflectance values and TRS indicated that simple models could be developed that described much of the variability present in stalk sucrose levels. Several regions appeared to be important in describing stalk sucrose levels, including; the ultraviolet (250-330 nm), blue, green and yellow (450-590 nm), orange and red (590-650 nm), and the near-infrared (740-850 nm). These combined results indicate that it may be possible to utilize remote sensing techniques to estimate sugarcane maturity (TRS) prior to harvest.