Effect of nitrogen fertilizer, planting pattern and plant density on root yield and quality and physiological indices of sugar beet (Beta vulgaris L.) cv. Pars under tape-drip irrigation condition

Effect of nitrogen fertilizer and plant density on root yield, quality and physiological traits of sugar beet (cv. Pars) under tape-drip irrigation condition was assessed in strip factorial plot arrangement using randomized complete block design with four replications. Two levels of planting patterns (40-60 cm and 40-50 cm) and four levels of nitrogen fertilizer; zero (N0), 50% (N1), 75% (N2) and 100% (N3) of the recommended levles for furrow irrigation) were assigned to vertical plots and two levels of row spacing (14 and 20 cm) randomized in horizontal plots. The experiment was carried out in two succeive sugar beet growing seasons (2013 and 2014) in the research field station of of Sugar Beet Research Institute, Karaj, Iran. Nitrogen fertilizer had significant effect on root and sugar yields. Decreasing nitrogen fertilizer to 75% of recommendation didn’t significantly influence root and sugar yields. The least and highest nitrogen accumulation of 99.9 and 240.3 kg.ha-1 were measured at zero and 100% levels of recommended nitrogen fertilizer, respectively. Accumulated nitrogen was partitioned greater in roots (58%) than shoots (42%). The highest Nitrogen Use Efficiency (NUE) for producing sugar was 50.8 (50.8 kg of sugar.kg-1 of nitrogen) in the treatment without nitrogen fertilizer application which was 21.7, 24.8 and 31.3 percent higher than treatments with 50%, 75% and 100% of recommended nitrogen fertilizer, respectively. Radiation penetration under the canopy showed that more radiation was intercepted in denser plant population and higher nitrogen fertilizer applications. Nitrogen fertilizer had significant effect on physiological traits such as SPAD value, chlorophyll content, maximum photochemical efficiency of photosystem II (Fv/Fm) and number of leaves. It was concluded that tape-drip irrigation system could reduce 25% of nitrogen fertilizer application without significant changes in important qualitative, quantitative and physiological traits of sugar beet.