1Aristotle University of Thessaloniki, Faculty of Agriculture, Laboratory of Agronomy, 541 24 Thessaloniki, Hellas.
2Hellenic Sugar Industry SA, Agronomic Research Service, 574 00 Sindos, Hellas.
In a four-year experiment, five nitrogen rates (0, 60, 120, 180 and 240 kg N ha-1)
were tested over irrigated sugar beets grown on clays, underMediterranean
conditions, in centralGreece. There, sugar beets are commonly grown under water
shortages, high temperatures and high soil Na concentrations. Contrary to previous
reports, N rates did not affect significantly population density (as assessed by root
number at harvest) and sucrose content in fresh and dry root weight (SC and SCD,
respectively). Yield response to N was year dependent and only in one out of four
seasons, was there a positive effect of N on sugar yield and white sugar yield. In
that case, the estimated optimum N dose was high (220 kg N ha-1). Increasing N
rates increased significantly N assimilation (as assessed by petiole NO3-N and root
α-amino N) and water content in root (WCR) but decreased biomass partitioning to
root (lower harvest index). Selective absorption (SA, the preferential uptake of K
over Na in roots) decreased with increasing N rates and it was negatively correlated
with sugar beet N nutrition indices (petiole NO3-N and root α-amino N). A
negative correlation between SA and petiole NO3-N was also evident when data
combined over years, indicating that strong Na exclusion was associated with poor
N nutrition, a contradiction to previous reports. The higher the SA, the lower the
WCR indicating less dilution of sucrose in root and thus, the higher the SC.
Moreover, high SA evoked sucrose accumulation in roots as it was shown by its
positive correlation with SCD.