Rates of nitrogen supply during different developmental stages affect yield components of safflower (Carthamus tinctorius L.)

Abstract

Abstract The yield components of two safflower (Carthamus tinctorius L.) lines have been studied in glasshouse experiments. Three nitrogen supply rates were used in each of three developmental phases: emergence to the beginning of stem-internode elongation, from stem elongation to when the terminal capitular bud became visible, and from then to maturity. The major component of yield was the number of capitula per plant. The successive orders of branches, primary to quarternary, are each terminated by capitula. The number of secondary capitula was determined by the nitrogen supply rates between the time of stem elongation and when the terminal bud became visible; the number of tertiary capitula by the nitrogen supply after both stem elongation and bud visibility; and the number of quaternary capitula by the nitrogen supply after terminal bud visibility. The number of filled seeds per plant was linearly correlated with the number of capitula which in turn was linearly related to the dry weights of the plants. This relationship differed between the two genotypes used: Gila and an experimental line, A1110. Total plant dry weights and nitrogen contents were positively affected by nitrogen supply rates after stem elongation, as were the separate organs: leaf laminae, stem + petioles, and roots. Single seed weights did not differ much between nitrogen supply rates, and the only significant effect of nitrogen supply on oil concentration in the seeds was a depression by the highest rate after bud visibility. The product of these yield components, oil yield per plant, was significantly affected by the nitrogen supply rates between stem elongation and bud visibility. The nitrogen concentration in seeds was only affected by nitrogen supply rates after bud visibility; there were differences in the response of the two genotypes. The results show that the most efficient time of application of nitrogen fertilizer to safflower crops is at stem elongation.