Developing, validating and applying near infrared (NIR) spectroscopic methods for the nutrient compositional analysis of sugar mill byproducts

THE IMPLEMENTATION OF the Reef Protection Act 2009 has seen the Australian sugar industry adopt measurement driven systems for nutrient application. Recent attention on the application of sugar mill by-products to the cane field has encouraged the development of rapid and cost-effective methods for the determination of nutrient composition of mill mud and mill ash products. Near infrared (NIR) spectroscopic methods for these analyses surpass several facets of traditional wet chemistry methods, dramatically reducing costs, required expertise and chemical exposure, while increasing throughput and access to data. Further, this technology can be applied in various modes including laboratory, at-line and on-line installations, allowing measurements to be taken at different sampling points. Application of NIR methods for the nutrient analysis of mill byproducts has been previously conducted on a small scale, but this paper presents an extended investigation including data covering multiple milling regions across several crushing seasons. Mill mud samples were obtained from four mills over the 2009-12 crushing seasons. Each sample was analysed using traditional wet chemistry methods for the nutrient elements carbon, nitrogen, phosphorus, potassium, calcium, magnesium, and sulphur, and scanned by an NIR instrument. Partial least squares (PLS) regression models were used to build calibrations for each constituent, targeting a combination of high R2 values and low standard errors of calibration and validation. These calibrations were subsequently validated with data collected on a millbased NIR system in the 2012 crushing season. This work has demonstrated the success of NIR technology for the use of rapid, cost effective nutrient analysis in the milling environment.