Quantifying Response of Safflower Seedling Emergence to Temperature

The main objective of this study was to describe emergence rate response to temperature and estimate cardinal temperatures (base, optimum and ceiling temperatures) and biological days requirement for safflower emergence. To do this, four safflower cultivars (Esfahan, Goldasht, Padideh and Sofeh) were sown at 12 sowing dates (every month) and the emergence rate (inverse of time to 50% emerged seeds) was calculated for each sowing date. The segmented, dent-like and beta functions were used to describe the relationship between emergence rate and temperature. Root mean square of deviation (RMSD), coefficient of variation (CV), correlation coefficient (r) and linear regression coefficients (a, b) between predicted and observed days to emergence were used to select the superior function. Results indicated that the compared to the dent-like and beta functions, the segmented function described well the response of safflower emergence to temperature due to the higher r (0.90-0.97), and lower RMSD (2.17- 4.06) and CV (12.3-22.4). Fit of the segmented function on data of emergence rate to temperature showed cardinal temperatures (base, optimum and ceiling temperatures) among cultivars ranged from 2.30-3.44, 20.56-23.28 and 35oC, respectively. There was no significant difference among the cultivars in terms of cardinal temperatures. The biological days requirement for emergence among cultivars ranged from 8.05 to 9.78 which were not different significantly. The quantitative information provided by this study can be used in the crop models to predict the emergence time courses under diverse temperature conditions.