Effect of irrigation regimes on agronomic traits of safflower (Carthamus tinctorius L.) under different levels of K fertilization

In order to study the effect of irrigation regimes on agronomic traits of safflower (Carthamus tinctorius L.) under different levels of K fertilization, a factorial experiment was carried out in research field of Qazvin, Iran in 2009-2010 based on a Randomized Complete Block Design with three replications. The studied factors included irrigation treatment at four levels (based on 60, 100, 140 and 180 mm cumulative evaporation from Class-A evaporation pan) and K fertilization levels at four levels (including 0, 50, 100 and 150 kg.ha-1 from potassium sulfate source). Results showed that the increase in irrigation level significantly increased 1000-seed weight, seed yield, seed oil content, oil yield, biological yield and harvest index, so that they were increased by 58, 110, 9, 126, 85 and 14% with the increase in irrigation level from irrigation based on 60 mm evaporation to irrigation based on 180 mm evaporation, respectively. Also, higher K fertilization levels resulted in significant increase in all traits except harvest index, so that these traits showed 34, 58, 15, 79, 54 and 3% increase with the increase in K fertilization level from 0 to 150 kg.ha-1 and only the increase in harvest index was not significant. The interaction between irrigation treatments and K fertilization levels was insignificant for all studied traits but 1000-seed weight, seed yield and oil yield. Under the treatment of irrigation based on 60 mm evaporation, the increase in K fertilization level from 0 to 150 kg.ha-1 resulted in 20, 35 and 52% increase in 1000-seed weight, seed yield and oil yield, respectively. But under the treatment of irrigation based on 180 mm evaporation, the increase in K fertilization level led to 53, 130 and 168% increase in these traits, respectively. Results revealed that the increase in K fertilization level mitigated the adverse effects of low-irrigation regimes on agronomic traits of safflower.