Effect of Nitrogen Rates on Yield, Non-Sugar Impurities and NUE of Four Sugar Beet Varieties under Drip Irrigation Conditions

To evaluate the effect of nitrogen (N) fertilization rate on quantitative and qualitative characteristics of drip-irrigated sugar beet, a two-year field experiment was carried out in two areas of Iran including Karaj and Moghan. Four different amounts of N fertilizer (no applied (N0), optimum rate (N100), 75% (N75) and 50% (N50) of optimum rate) and four varieties included two European varieties (Rosire and Flores) and two Iranian varieties (Pars and Ekbatan) were experimental treatments. The results in Moghan showed that the highest values of root and sugar yield were related to N75 by 74.09 and 9.13 t ha-1, respectively. Flores and Rosier had greater sugar yield than Pars and Ekbatan varieties in both locations. Our findings in Karaj demonstrated that SC decreased with increasing N rate, however there was no significant difference among nitrogen levels in SC in Moghan. N application rate had no significant influence on content of the non-sugar impurities in both areas except K concentration. As data, European varieties contained lower non-sugar substances and higher root quality than Iranian varieties. In addition, greater nitrogen use efficiency (NUE) was gained in European varieties compared to Iranian varieties. Increasing N application rate also caused to decrease in NUE under two area conditions. The greatest NUE occurred by no application of N fertilizer as 46.13 and 45.35 kg sugar kg-1 N in Moghan and Karaj, respectively. In general, N fertilizer consumption can be reduced to 75% of the recommended N rate under the drip irrigation system that is developing in the country.