Using of chlorophyll meter for recognize nitrogen deficiency in sugar beet

In order to use chlorophyll meter (SPAD) to recognize nitrogen deficiency in sugar beet plants and used to predict the appropriate timing for fertilizer top-dressing in sugar beet a research was conducted using various levels of nitrogen fertilizer during different growth stages of sugar beet plants in the research farm of Sugar Beet Seed Institute located in Karaj during 2007, using a split plot design in time based on Randomized Complete Blocks in four replications. Five level of pre-sowing nitrogen from the source of urea was applied in amounts of 0(as control), 120, 160, 200 and 240 kg/h considered as main plots and plant growth stages as sub plots. Chlorophyll concentration in 5th leaf blade was measured by chlorophyll meter (SPAD) at five growth stages based on the number of leaves on sugar beet plants including (GS1:3-6, GS2: 6-12, GS3:12-15, GS4:15-18, GS5:18-20) leaves of each plot. In the same leaves, concentrations of nitrogen (by Kjeldahl method) and chlorophyll a, b and a (by Spectrophotometer) were measured. Results from regression analysis on the leaf number 5 showed that there was higest significant correlation between chlorophyll reading and nitrogen on a leaf area basis and on a dry-weight basis, and total nitrogen and concentration of chlorophyll (a, ab) in 12- 15 leave stage. Also results of this experiment showed that the chlorophyll meter reading were influenced by the growth stage and sampling time and the level of used nitrogen fertilizer. Nitrogen fertilizer and different growth stage had significant effect on the chlorophyll meter reading. The least number read from SPAD was 34 in 3-6 leaf stage, which associated with no-applied nitrogen treatment. Threshhold of chlorophyll meter was estimated 39/1 in this study in 12-15 leave stage, this threshold can be used as a criteria to compare. According to the obtained results, chlorophyll meter can be used as a simple, rapid and non-destructive instrument to determin chlorophyll concentrations in a leaf during 12-15 leaf stage and to recognize nitrogen deficiency in sugar beet plants and can be used to predict the appropriate timing for fertilizer top-dressing after of calibiration for region in sugar beet.