The effect of form and level of inorganic N on nitrogen use efficiency of sugarcane grown in pots.

To-date, assessments of nitrogen use efficiency (NUE) of sugarcane have not included the contribution of its components, nitrogen uptake efficiency (NUpE) and nitrogen utilization efficiency (NUtE). This study determined these values, based on biomass and plant nitrogen (N) content, in two fourmonth- old pot-grown genotypes. The treatments included six N regimes, with nitrate (NO3-N) or ammonium (NH4+-N) supplied alone, or as NO3--N for the first 6 weeks and then NH4+-N until harvest, each as 4 or 20 mM. Regardless of the N form, NUE was higher at four than at 20 mM due to significantly higher NUpE at low N supply. The results indicated that there was luxury N uptake and preference for NH4+-N nutrition, which resulted in the highest determined NUE. There were significant differences between genotypes in biomass, morphological growth parameters, N uptake, total plant N and NUE, the latter matching previously established sucrose yieldbased NUE field rankings. [ABSTRACT FROM AUTHOR]