I recently read an article in the NIR News magazine about the use of NIR to analyze some sugar mill by products. One of the products is the boiler ash. Boiler ash is generated after burning the bagasse, which is one of the sugar mill byproducts. This boiler ash is rich in potassium and silicon.
See this nice video from India about the use of bagasse to generate electricity:
Boiler ash is used in combination with mill mud (another sugar mill by product) to fertilize the sugar cane fields. Mill mud is rich in Calcium and Phosphorous.
In this video you can see in the minute 5:11 aprox the phase when the mill mud is generated.
NIR can measure inorganic constituents because there are organic molecules which interact with minerals, also by indirect correlations or by the way their influence in the hydrogen bonding within the sample matrix.
NIR News Vol3 No1 January/February 2012