EVIDENCE OF DIFFERENCES IN NITROGEN USE EFFICIENCY IN SUGARCANE GENOTYPES

MORE efficient use of N in cropping systems can be achieved through improved N management practices combined with genetic improvement of the crop. In this paper we outline traits that may contribute to nitrogen use efficiency (NUE) in sugarcane. We also provide initial biomass and root trait results from a N × genotype pilot field trial in which five unselected genotypes and Q117 were compared for biomass accumulation at two N supply rates (zero and 100–140 kg urea-N/ha/y). In the second ratoon crop, genotypes differed in biomass accumulation at the two N rates. Q117 and two unselected mapping genotypes (KQ99-1387, KQ99-1484) were responsive to N additions and produced less than 50% of the biomass under zero N addition compared with added N fertiliser. In contrast, KQ99-1355 was less responsive to N supply, and grown without added N fertiliser, produced up to 70% of the biomass at high N supply. Genotypes differed in root morphology and distribution. Compared to the other genotypes, KQ99-1355 had a greater root biomass in proportion to stool size and had a dense surface mat of fine roots at both N supply rates. The results confirm those from glasshouse studies that genotypes differ in NUE.