SUSTAINABLE SUGARCANE PRODUCTION SYSTEMS: REDUCING PLANT NITROGEN DEMAND

THE LARGE amounts of nitrogen (N) fertiliser applied to most modern cropping systems support high yields but can also cause off-site N pollution. More efficient use of N in cropping systems can be achieved through improved N management practices combined with genetic improvement of the crop. We studied sugarcane genotypes in the field and in controlled glasshouse conditions to identify traits that confer nitrogen use efficiency (NUE) to sugarcane. There was no effect of N application on biomass in the plant crop of the field trial. In the first ratoon biomass production was significantly affected by N supply and genotype but no significant interaction was observed. In controlled glasshouse experiments, genotypes differed in N allocation to stalk and leaves. Storage of N in stalks could be useful if N is remobilised to N-sink tissues later in the growing season. Genotypes differed in leaf turnover and inefficient remobilisation of N from senescent leaves could reduce NUE. Photosynthetic NUE (amount of N in leaf per unit CO2 fixed) was examined as a potential screening tool but was not useful to determine instantaneous genotype performance at low/intermediate N supply. Overall, there are numerous traits which could be exploited for future breeding of NUE sugarcane cultivars. This integrated research on NUE at plant and system levels will enable more targeted N supply with reduced N application rates and associated losses while maintaining yields in Australian sugarcane farming systems.