Effect of nitrogen application on quantitative and qualitative of sugar beet cultivars

Background and objectives: Over the last two decades, a large number of researches have been conducted regarding the importance of nitrogen in sugar beet. This indicate that there were needs to investigate more on nitrogen management to achive higher production and quality because less nitrogen application result in reducing yield and high nitrogen application would increase production costs and eliminate sugar beet quality. Accordingly, this research was carriod out to investigate the interaction effects of nitrogen × cultivar on some quantitative and qualitative traits of sugar beet in Khorasan province, Iran.

Materials and methods: A field experiment was carried out in Research Field of the Ferdowsi University of Mashhad during 2008-2009 growing season. The experiment was a randomized complete block design based on factorial arrangement in three replicates. Factor A was cultivar at three levels (Magnolia, Fiama and Nagano) and factor B was nitrogen applications at four levels (control, 80, 160 and 240 kg N ha-1). For measurement of qualitative traits in sugar beet such as sugar content, sucros concentration, Na, K, N, Alkaloids and Molasses sugar, a sample was taken from each plot and sent to laboratory. Then, white sugar yield, gross sugar yield and extraction coefficient of sugar was calculated using the measuted qualitative traits. Also, nitrogen concentration in both above-ground biomass and storage organe was measured at 101 and 190 days after sowing using Kjeldahl method.

Results: Results showed that nitrogen application significantly affected above-ground biomass, N concentration in root and above-ground biomass and all qualitative traits except potassium concentration in root. In addition, the interaction effects on N in root and all quantitative traits except white sugar yield and gross sugar yield were significant. The highest root yield was observed for Fiama (120 ton ha-1) under application of 240 kg N ha-1 while the highest above-ground biomass obtained 36.9 ton ha-1 with 160 kg N ha-1. Increasing N application led to increased N concentration in above-ground biomass (2.21 and 1.64 % in 101 and 190 days after emergence, respectively). The highest gross sugar content (POL) and SUGAR content obtained at control treatment (lack of N application) with 17.3 and 15.7 % respectively, while the lowest observed at 240 kg N ha-1. The results also showed that N and Sodium concentration in root were significantly increased in all cultivars with increasing of N application. Among N treatments, the highest molasses sugar observed at 240 kg N ha-1 (2.22 %) for Nagano.

Conclusion: It sould be concluded that nitrogen application would increase root yield while affecting the quality of sugar beet. The highest root yield obtained in Fiama cultivar with 80 kg of nitrogen application. Higher nitrogen application resulted in increased Na, N in root and reduced extraction efficiency of sugar. Also, increased nitrogen application led to an increase in above-ground biomass and lower root yield.