Effects of potassium supply on growth and yield of safflower as compared to sunflower

Safflower may have a certain production potential under German conditions, particularly in organic farming where the putatively low nutrient requirement is highly welcomed. However, current knowledge regarding the nutrient requirements of safflower as compared to similar oil crops is limited. It was thus the aim of this study to determine the growth and yield response of safflower (Carthamus finctorius L.) as compared to sunflower (Helianthus annuus L.) with respect to potassium (K) supply. Three safflower and two sunflower plants were cultivated in 5 L Mitscherlich pots. Both species responded strongly to increasing K supply with respect to plant growth and yield. Growth and yield of safflower increased up to 1 g K per pot, while the optimum for sunflower was 3.0 g K per pot. Safflower out-yielded sunflower at low K supply, while at high K level, the opposite was observed. Supply of K affected virtually all yield components in both species, though to different degree. The number of capitula in safflower was only slightly affected, and the number of achenes per capitulum was only reduced under severe K deficiency, while single-achene mass increased with increasing K supply. In sunflower, the number of achenes per capitulum strongly responded to the K supply, as did the single-achene mass. Oil yield in safflower was affected by K deficiency mainly due to reduced achene yield, not oil concentration. However, oil yield in sunflower was severely affected by low K supply due to both reduced achene yield and lowered oil concentration. Multiple-regression analyses indicate that in sunflower, the stem dry matter (DM) and the total amount of K accumulated in the aboveground biomass were most important, while in safflower the total amount of K and N accumulated had the highest impact. It is concluded that sunflower is more sensitive to inadequate K supply than safflower.