Assessing light interception and light extinction coefficient on planting dates of different cultivars of wheat in Esfahan region

Appropriate cultivar and date of sowing are two of the most critical aspects of crop management in semi arid condition with low rainfall like Iran. An experiment was conducted in 2008–2009 in khaton Abad Agricultural Research Station of Islamic university of khorasgan branch, Esfahan, Iran. A split plot layout within randomized completely block design with 3 replications was used. Different planting date levels were in 3 levels including (22th October , 6th November, 2th December) as the main plot and cultivars were in 6 levels including [Kavir and Shiraz (with spring growth habit) , Alvand and Mahdavi (with facultative growth habit) , Gaskoghen and C81 – 14 line (with winter growth habit)] as the subplot. Planting date has significant effect on LAI, total dry matter, NAR, light interception and light extinction coefficient, the number of seed per spike, a thousand seed weight and seed yield. CGR was not affected by planting date, and no trend was found. The influence of cultivar of LAI, total dry matter, NAR, light interception, light extinction coefficient, a thousand seed weight and seed yield was significant. Planting date and cultivar interaction just had significant effect on LAI and light interception. Gaskogen had obtained the highest seed yield and the maximum a thousand seed weight was achieved in C81-14. C81-14 also had obtained the highest LAI, light interception and light extinction coefficient. Plantation on 22th Oct had obtained the maximum LAI, light interception, light extinction coefficient, the number of seed per spike, a thousand seed weight and seed yield.


Introduction
Wheat (Triticum aestivum L.) is the most commonly planted and used crop in the world (Aydin et al., 2010;Sohrabi et al., 2010;Robiul Islam et al., 2011). Khah (2009) and Barradas and Lopez-Bellido (2009) noted that selection of the planting date is one of the most important management decisions for crop production. When the proper planting date is selected, a cultivar with a suitable growth period can flower and produce seed in a proper time (Yarnia et al., 2010). Awal et al. (2006) reported that the intensity of solar radiation will remain relatively constant and represented a resource that could be used more efficient for crop production. Svirezhev and Steinborn (2001) concluded that a continuous measurement of the components of the radiation balance for different types of vegetation had become an almost standard procedure giving us information about the transformation of incoming solar radiation by vegetation. Falconer and Mackay (1996) reported that to measure environmental interaction and to see interaction variance, different genotypes are reared or grown in a range of environments. Wheat grain yield is the end product of the interaction of a large number of physiological and biochemical process in the plants (Dere and Yildirim, 2006). So the aim of this study is to determine the light interception and light extinction on planting dates of different cultivars of wheat in Esfahan region.

Material and Methods
This experiment was conducted in 2008-2009 in khaton Abad Agricultural Research Station of Islamic university of khorasgan branch, Esfahan, Iran. A split plot layout within randomized completely block design with 3 replications was used. Different planting date levels were in 3 levels including (22th October , 6th November, 2th December) as the main plot and cultivars were in 6 levels including [Kavir and Shiraz (with spring growth habit) , Alvand and Mahdavi (with facultative growth habit) , Gaskoghen and C81 -14 line (with winter growth habit)] as the subplot. Each plot included 5 meter length and 2 meter width with 10 planting rows. The distance between each row was 20 cm, and the distance between plants on the row was 1.25 cm. All seeds were planted at the depth of 3-4 cm. Plant density for all plots were similar and equal to 400 plants per m 2 . The soil preparation consisted of mouldboard ploughing, followed by discing and smoothing with a land leveler. Nitrogen fertilizer as urea (45% pure N) (300 kg urea per ha) was used in different sections for better plant , s utilization (before irrigation, tillering stage, stem elongation stage). The first irrigation was done immediately after seed plantation. Other irrigations were done on the basis of plant , s requirement (9 days interval). Rows number 1, 3, 5 and 10 and 0.5 meter (50 cm), primer and edge lines were discarded from sampling. For determining light transmission (T), solar radiation interception (A) and extinction coefficient (K), equation number 1 , 2 and 3 were used respectively. I and I0 mean the solar radiation under plant canopy and solar radiation absorption above of plant canopy. (1) K= -Ln (I/I0) / LAI (3) Data were subjected to analysis of variance (ANOVA) using statistical analysis system, followed by Duncan , s multiple range test and differences were considered significant at P<0.05 by MSTAT-C software.

Results and discussion
Planting date has significant effect on LAI, total dry matter, NAR, light interception and light extinction coefficient, the number of seed per spike, a thousand seed weight and seed yield. CGR was not affected by planting date, and no trend was found. The influence of cultivar of LAI, total dry matter, NAR, light interception, light extinction coefficient, a thousand seed weight and seed yield was significant. Planting date and cultivar interaction just had significant effect on LAI and light interception (Table 1). Soleymani et al. (2011) reported that solar radiation absorption was significantly affected by cultivar. The highest LAI and total dry matter was obtained in 22th Oct. The differences in LAI between all planting dates treatments were significant. 22th Oct and 2th Dec had no significant difference in total dry matter with each other. The leaves, being the site of photosynthetic activity, appear to have an obvious relationship to the plant , s grain yield ability (Dere and Yildirim, 2006). 2th Dec had obtained the maximum NAR, that had just significant difference with 22th Oct. The maximum and minimum light interception was achieved in 22th Oct and 2th Dec, respectively. The highest light extinction coefficient and the number seed per spike was related to plantation on 22th Oct. Awal et al. (2006) noted that efficient use of solar radiation is one of the major criteria for obtaining a yield advantage through intercropping. A thousand seed weight was significantly decreased from 22th Oct to 2th Dec. Seed yield was significantly differed between planting dates treatments. The highest seed yield was related to 22th Oct, and this treatment had significant difference with two other treatments. The highest LAI and total dry matter was related to C81-14. C81-14 had no significant difference in LAI with Alvand, Mahdavi and Gaskogen. The highest and the lowest NAR was obtained in Kavir and C81-14, respectively. Aydin et al. (2010) concluded that some genotypes are more affected from one environment than another one due to environmental differences. C81-14 had obtained the maximum light interception and light extinction coefficient, and this cultivar had significant differences with all other cultivars. The maximum and minimum number of seed per spike was 31.94 and 27.96, that was related to C81-14 and Shiraz, respectively. C81-14 also obtained the maximum a thousand seed weight. There was no significant difference in a thousand seed weight between Gaskogen and C81-14. The highest seed yield was obtained in Gaskogen. This cultivar had significant differences with all other cultivars, expect of Kavir (Table 2). Planting seeds on suitable date maximize the growth duration and complete seed maturation lead to maximize the growth duration and complete seed maturation lead to maximal yield and reduced the risk of unfavorable environmental conditions (Yarnia et al., 2010). The maximum a thousand seed weight was obtained in 22th Oct and C81-14 interaction. The highest seed yield was related to 22th Oct and Gaskogen interaction ( Table 2).

6771.83e
Common letters within each column do not differ significantly.

Conclusion
Appropriate planting date management for each cultivar in a region is considered to be the most important manageable factor in plant production, that does not promote excessive crop growth that delays maturity (Ali et al., 2009;Barradas and Lopez-Bellido, 2009). Gaskogen had obtained the highest seed yield and the maximum a thousand seed weight was achieved in C81-14. C81-14 also had obtained the highest LAI, light interception and light extinction coefficient. Plantation on 22th Oct had obtained the maximum LAI, light interception, light extinction coefficient, the number of seed per spike, a thousand seed weight and seed yield.