Nitrogen management has been intensively studied on several crops and recently associated with variable rate application on-the-go based on crop sensors. On sugar cane those studies are yet scarce and as a biofuel crop the input of energy matters, looking for a high positive balance of biofuel production and low carbon emission on the whole production system. This paper shows the first results obtained using a nitrogen and biomass sensor (N-SensorTM ALS, Yara International ASA) aiming to indicate nitrogen application demands on commercial sugar cane fields. Eight commercial fields located in one Sugar Mill in the state of São Paulo, Brazil, varying from 15 to 25 hectares in size, are being monitored. Conditions vary from sandy to heavy soils and the previous harvesting occurred from the beginning of the current season (May, 2009) to late season (October, 2009), including first, second and third ratoon stages. Each field is being scanned with the sensor four times in the season (20, 40, 60 and 80 cm of stem height), followed by tissue sampling for biomass and nitrogen uptake on ten spots inside the area, guided by the different values shown by the sensor. Soil samples for nutrients monitoring are also being taken in a one hectare grid. The results up to now show high correlation between the sensor values and sugar cane biomass and nitrogen uptake, giving support to the potential use of this data to elaborate algorithms to manage variable rate application of nitrogen for sugar cane.