Growth analysis is a valuable method in the quantitative analysis of crop growth, development and crop
production. In order to evaluate effects of nitrogen rates and plant density on physiological growth indices
of safflower, an experiment was conducted at Khorramabad, Lorestan province in 2008. The experiment
was carried out as split plot in basis of randomized complete block design with four replications. Three
nitrogen application rates were as main plots (N1=control, N2=75 and N3=150 kg/ha net nitrogen) and
plant density was as sub plots in 3 levels (D1=40, D2=50 and D3=60 plant/m2). The growth degree day
index was used to examine more closely fitting growth curves using non-linear regression models.
Appropriate model was selected for each growth index. The results showed that application of nitrogen
led to increasing of growth indexes including leaf area, total dry matter and crop growth rate. But, net
assimilation rate was reduced. Growth indexes such as, leaf area, total dry matter, did not change with
increasing plant density, due to branching of safflower. However, crop growth and net assimilation rate
were reduced in plants. Overall, the results show that applied nitrogen has a more positive effect on
safflower growth index compared to density changes.