Effect of leaf position and age on the nitrogen content and chlorophyll meter values in sugar beet

To investigate the effect of sugar beet leaf age and position on nitrogen content and chlorophyll meter readings (SPAD value) using chlorophyll meter in sugar beet, a field experiment was conducted in the experimental field of Sugar Beet Seed Institute (SBSI) in 2007 cropping serason, using a split-spli plot in time arrangement in RCBD with four replications. Five levels of pre-sowing nitrogen in the form of urea 0 (as control), 120, 160, 200 and 240 kg.ha-1 were assigned to main plots and five plant growth stages considred as sub plots. Chlorophyll meter readings of sugar beet leaf blade number 5, 10 and 15 were determined by chlorophyll meter (SPAD-502) at five growth stages based on the number of leaves including 3-6, 6-12, 12-15, 15-18 and 18-20 leaves of each plant. In the same leaves, concentrations of nitrogen content (Kjeldahl method) and chlorophyll a & b were measured. Analysis of variance showed that main effect of nitrogen fertilizer was significant for SPAD value (P<0.01) and nitrogen content(P<0.05). The main effect of growth stage was also significant for nitrogen content (P<0.05) and specific leaf weight (P<0.01). All measured sugar beet traits were affected by the main effect of plant growth stage. The interaction between nitrogen fertilizer × growth stage was only significant (P<0.05) for leaf nitrogen content. However, the interaction between growth stage × leaf number was significant for all measured traits of sugar beet. There was significant correlation between the SPAD value and nitrogen content of leaf, based on dry weight, in leaf nuber 5, while there was no significant correlation between the SPAD value and nitrogen content of leaf in the leaf number 10 and 15. In conclusion, chlorophyll meter reading and nitrogen content of sugar beet leaves were influenced by leaf age and position. Thus, fully expanded leaf number five may be used for chlorophyll meter reading and determination of nitrogen content in sugar beet in 12-15 leaves stages.