Seedling emergence response to temperature in safflower: measurements and modeling

Quantitative information about the response of seedling emergence totemperature for safflower (Carthamus tinctorius L.) is rare. The main objective ofthe present study was to develop a model for predicting days to emergence forsafflower as influenced by the temperature. In this regard, a field experiment with arange of sowing dates and four safflower cultivars were conducted to describe theresponse of seedling emergence to temperature and determine cardinaltemperatures and biological days required for emergence (number of days toemergence under optimum temperatures). The segmented, dent-like and betafunctions were used to describe the response of seedling emergence to temperature.Results showed that the segmented function described well the seedling emergenceresponse to temperature with the cardinal temperatures of 3.4, 22 and 35 °C forbase, optimum and ceiling temperatures, respectively. The biological days requiredfor seedling emergence was estimated 8.6 days. Based on the findings, a seedlingemergence model was conducted which can estimate time to 50% of emergenceunder variable temperature conditions. Model evaluation by using the someindependent data showed that the model predicted time to 50% of emergenceaccurately (RMSD=1.3 days and R2=0.92).