determination of sugar beet extinction coefficient and radiation use efficiency at different plant density and nitrogen use levels

extinction coefficient (k) is an important index that shows the rate of light decrease in canopy. net biomass accumulation is linearly related to cummulative light interception. the slope of this relationship is termed radiation use efficiency. a split plot experiment within randomized complete block design with three replications was conducted in april 2001 in sugar beet research station in kamal abad, karaj. the main plots were sugar beet plant densities (d1=80000, d2=100000, d3=120000 p/ha) and subplots were nitrogen fertilizer in three levels (n0=100, n1=200, n2=300 kg n/ha). the plots were sampled 11 times during growth season and leaf area index, radiation use efficiency, extinction coefficient and total shoot biomass were measured. there was no significant difference in radiation use efficiency among the treatments and it was about 0.008 kilogram per meter square. the extinction coefficient was about 0.56. the effect of treatments on leaf area index and total dry weight wasn’t significant, however the most lai in plant density treatment was related to 80000 plants per hectare and among nitrogen fertilizer treatment was related to 300 kg/ha nitrogen. 80000 plants/ha with 200 kg/ha nitrogen and 100000 plants/ha with 300 kg/ha nitrogen had the most top dry matter.