Efficiency of nitrogen uptake and utilization in sugar beet genotypes

The nitrogen use efficiency (NUE) is composed of the nitrogen uptake (NUpE) and nitrogen utilization efficiency (NUtE). The contribution of these components to overall NUE of sugar beet genotypes is unknown, as well as the reasons for genotypic variation. In 2018 and 2019, 6 genotypes were studied in field trials at three N levels (65, 120, 240 kg N ha(-1)). The trials revealed only minor genotypic differences in N uptake and N uptake efficiency, but distinct genotypic differences in N utilization efficiency and NUE. The interaction between genotype and environment was negligible, i.e. differences between genotypes in NUE were independent of N management, and there was no genotypic adaptation to low N availability. Differences in NUE resulted rather from differences in sugar yield potential. This demonstrates that selection to high sugar yield potential will also promote NUE. It was concluded that a high sugar yield potential resulted from an assimilate partitioning towards high sugar yield, in combination with a low leaf mass to total dry mass ratio. There was evidence that lower leaf mass resulted in higher levels of leaf N content. If a higher leaf N content could be used to identify high yielding genotypes is unclear, but it was concluded that a high leaf mass is not a prerequisite for high sugar yields.