Nitrogen (N) is a fundamental nutrient in agroecosystems, but has considerable negative environmental impact when used in excess. Meeting N demand while reducing excess N can be achieved through improvements in N use efficiency (NUE) of a crop agroecosystem. Non- destructive methods and sampling procedures for estimating biomass, N and 15 N content during various phases of sugarcane crop development were tested to evaluate NUE. Allometric relationships appeared to be an effective method of estimating aboveground biomass from cane height. The third leaf below the top visible dewlap was found to have an 15 N content sufficiently representative of crop above ground biomass. Further, the use of a dilution curve was found to be an effective means of estimating N content from cane biomass. Using these methods, average 15 N recovery 2 and 4 months after urea application was determined for the sugarcane aboveground biomass, belowground biomass and the soil compartment as 15.0±0.1 %, 9.2±1.2 % and 15.6±0.1 %.