Prediction of Phenological Development Stages of Safflower cv. Goldasht Based on Temperature and Day Length in Isfahan Region in Iran

Modern agriculture often needs exact information about occurrence of crop phenological development stages that have many applications. Data from sowing date trials conducted in the Kaboutarabad Agricultural Research Station, Isfahan during 2003-2009 were used to develop models for estimating phenological development stages of safflower cv. Goldasht. To estimate duration of each phenological development stage, the period of each stage were used as the dependent variable and various temperature variables, day length and combination of these variables as the independent variable in a step-wise regression analysis. A step of regression analysis was considered appropriate, when the highest R2 was accompanied by the significant (p≤ 0.05) regression coefficient and partial R2. The number of days from sowing to emergence, emergence to the commencement of heading, emergence to flowering, emergence to maturity and flowering to maturity were affected by sowing dates. Phenological development stages reduced as temperature increased. Day length had the highest effect on emergence to the commencement of heading and emergence to flowering periods and these periods reduced as day length increased. Tmean and T3max variables were entered in the regression model and explained about 89% of variation of duration of sowing to emergence. Duration of emergence to the commencement of heading was explained by DL × Tmax and DL2 × T2max with accuracy of %88. DL × Tmax was entered in the regression model and explained about %95 of variation of duration from emergence to flowering. DL × Tmax and T2mean explained the highest variance (85%) of duration from emergence to maturity. Tmin was the only variable entered in the regression model and explained about 58% of variation of duration from flowering to maturity.