EFFECTS OF VARIETIES AND NITROGEN FERTILISER RATE ON COLOUR AND CONDUCTIVITY LEVELS IN SUGARCANE

COLOUR and ash in raw sugar are two sugar quality attributes of high importance. Increased ash and colour levels increase refining costs and therefore lower market value of raw sugar. High ash levels also increase the loss of sugar to molasses. Some field related factors may affect ash and colour levels. Varieties and N fertiliser management are two factors that may be readily managed at a farm level, but possible tradeoffs with productivity need to be taken account of to maximise whole-of-industry profitability. This paper reports on experiments to quantify effects of varieties and N fertiliser, and their interactions on colour and ash (as measured via conductivity) in raw sugar. Varieties differed widely in colour/impurity levels and to a lesser extent in conductivity/impurity levels. Characterisation of varieties in final stage selection trials for colour and conductivity/impurity levels is recommended to better predict impact on industry profitability prior to possible industry release. Increased N fertiliser rates on average reduced colour levels in juice but increased amino N levels, which would have a net effect of increasing colour in raw sugar. However, it is recommended that N fertiliser management remain focused on optimising productivity because gains from reducing colour are small with potential losses in productivity from suboptimal fertiliser applications.