Prospects for a monitoring technique to improve N fertiliser decision-making are
explored. The technique is based on the nitrogen content of sugarcane juice at the mill.
This information would be used in decision making on N fertilisation rates on a specific
block basis in the subsequent season. Results from analysis of the N composition of
cane stalks produced under a diverse range of experimental conditions indicate
approximately 60--70% of the N in a cane stalk is contained in the juice. Conditions that
lead to high N supply (fertile soils, high N fertilisation rates, plant crops) result in high
amino-N levels in the juice. Under N deficiency, amino-N levels drop to very low
values. Water limitation interacts with N supply, and would need to be considered in
interpretation of results. Results from monitoring at Macknade Mill during the 1996
crushing season indicate that considerable variation exists in the amino-N composition
of cane supplied to the mill. Factors likely to be responsible for this variation are
discussed. Preliminary assessments indicate that up to half the cane supply contains
'excessive' levels of amino-N, suggesting considerable potential for savings in
fertilisation costs and improvements in juice quality, aside from any environmental
benefit of reduced N fertiliser inputs. Preliminary evaluation of NIR in amino-N
analysis shows good prospects for rapid and cost-effective analysis.