Studing extinction coefficient and radiation use efficiency in different cultivars of Safflower under different levels of Nitrogen (N) fertilizer

A high correlation existes between crop growth and the rate of radiation intercepted. The efficiency of radiation interception and absorption is dependent on leaf area index, light extinction coefficient and radiation use efficiency.To study extinction coefficient and radiation use efficiency in different cultivars of Safflower under different levels of N fertilizer, an experiment was carried out in the research field at the University of Valiasr in Rafsanjan during 2013-2014.
Experiment was arranged in a split plot design in complete randomized block design with four replication. Experiment factors inciuding N fertilizer were a main factor in 5 levels (control, 50, 100, 150 and 200 kg per hectare) and cultivar in 4 levels (Local Esfahan, goldashat, sofe and naeen). In addition to measuring the radiation above and under the canopy, the plots were sampled 8 times during growing season and leaf area index, total dry matter and finally light extinction coefficient and radiation use efficiency were measured.
The results showed that light extinction coefficient was not affected by N fertilizer but comparisom of extinction coefficient in difference cultivars showed that Goldasht cultivar have significant difference with Landrace of Isfahan and Soffah. and RUE obtained for endemic cultivars of Isfahan, Goldasht, Naien and Soffah were 0.46, 0.54, 0.48 and 0.46 respectively. Radiation use efficiency was influenced by N fertilizer; in this case, at fertilizer level of 150 kg, there was a significant difference among endemic cultivars of Isfahan, Goldasht, Soffah with control. At 200 kg level, Naien cultivar had a significant difference with control for RUE. There was no significant difference in obtained RUE in different cultivars and amount of RUE obtained for endemic cultivars of Isfahan, Goldasht, Naien and Soffah were 4.45, 4.19, 4.62 and 4.35 g / MJ, respectively. In addition, at fertilizer level of 100 kg /h, maximum leaf area index of all cultivars had a significant difference with control level.
In this experimental study with increasing the level of N fertilizer, maximum leaf area index also increased significantjy. Increasing the leaf area index caused radiation use efficiency be affected by N and generally in the highest level of radiation use efficiency obtained in N level 100 to 150 kg per hecter. It seemed that among the above cultivars, the most suitable one for radiation use efficiency was Naien cultivar.