Safflower growing degree days in different temperature regimes

Abstract

The plant growth and development are affected by many environmental factors, but the air temperature is the most effective one. During growing season plants accumulate growing degree days (GDD) or heat unit to complete a growth stage. Therefore, the GDD or HU is more accurate for prediction of developmental stages than number of days for different environmental and planting date. A field experiment was conducted in 2007-2008 at Kabotarabad Agricultural Research Station of Isfahan. Eight planting dates (March 5, March 20, April 3, April 18, May 4, May 19, June 5, and June 22) and three safflower cultivars (Arak, Sofea and Goldasht) were evaluated, using a randomized complete block design with split- plot layout in six replications. Dates of planting were considered as the main plot and cultivars were randomized in the sub-plots. Date of planting significantly affected number of days and GDD of developmental stages and seed yield. Delay in planting until seven planting date reduced seed yield and length of planting to emergence, emergence to head visible, emergence to flowering, emergence to ripening, planting to ripening and seed yield. These traits increased a little in eight planting date but GDD of these stages did not show any specific trend.   Cultivars significantly affected developmental stages duration and related GDD. Sofeh and Goldasht were the latest and earliest cultivars, respectively. There was no significant difference among seed yield of cultivars.