Seedling emergence response to temperature in safflower: measurements and modeling

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