Study on effect of plant density and N-fertilizer on radiation use effeciency and extinction coefficient in milk thistle (Silybum marianum L.) as a medicinal plant

Milk thistle (Silybum marianum) is an important annual/biennial herbaceous plant whichbelongs to the Asteraceae family. The effective substance of this plant (Silymarin) is used for chronic hepatits، liver toxic damages caused by alcohol and mushroom poisoning andstomachs problems treatments. To study the effect of plant density and N-fertilizer onextinction coefficient and radiation use efficiency (RVE)، an experiment in factorialexperiment with the base randomized complete blocks design with three replication wasconducted in spring 2005 at Research Station of Hammand Absard Damavand. Thetreatments were plant density in 3 levels (50×20 - 50×30 - 50×40 cm2) and N-fertilizer in 4 levels (0 – 50 – 100 – 150 kg/ha). During ontogenesis، the growth and development in each treatment were observed and leaf area index (LAI) and plant biomass were calculated to determine the extinction cofficient (K) and radiation use efficiency (RUE) in each treats ment. The results were analyzed with SAS program and the means were assessed by Duncan test at α=0. 05% and the curves were drawn with Excel program. The light measure operation in field was done 5 times and the results showed، that by an increase in plant density، the extinction coefficient would decreas، although the radiation use efficiency was increased but the difference levels of N-fertilizer hadn’t shown any effects on extinction coefficient and radiation use efficiency.