Effect of nitrogen supply on the production and distribution of dry matter in sugarcane

Abstract

Sugarcane productivity is probably limited by characteristically slow early growth and, later, by progressively decreasing leaf nitrogen (N) concentration. Increasing the N supply might increase productivity by influencing these attributes. In a pot experiment on two cultivars N was supplied at either a level corresponding to normal field supply (‘low’), or a level twice this (‘high’). Plants were sampled at 173 days, and then N level supplied to the remaining plants was either maintained or decreased until a final harvest at 270 days. Stem and total dry mass at 173 days were increased by c. 20% by high N, and at 270 days by c. 60%. Dry masses at 270 days were not affected by decreasing N supply at 173 days. Crop growth rate (C) between 173 and 270 days was increased about two and a half-fold by high N, because of both greater leaf area index (L) and net assimilation rate (E); variation in E was related to leaf N concentration. Sucrose yield was increased by c. 60% by high N supply because of greater stem dry mass rather than of increased sucrose concentration. The results suggest that augmenting the N supply during the early part of the growth period should increase productivity, but results from pots should be confirmed in the field.