LAUSR

Abstract This study was aimed to investigate the comparative effects of humic acid (HA) and fulvic acid (FA) on some growth parameters, antioxidant activity, and nutrient content of yarrow (Achillea millefolium L.) in the field and greenhouse conditions. Experimental treatments included HA and FA at concentrations of 5, 10, 15, and 20 kg ha−1 along with the control. The results of field and greenhouse experiments showed that the application of both HA and FA improved the growth parameters, photosynthetic pigments, and antioxidants of yarrow. In the field, the highest shoot dry weight was obtained from 15 kg ha-1 HA treated plants (with an 80 % increase compared to the control), while in the greenhouse experiment, the highest value was achieved from 20 kg ha−1 FA treated plants (with a 60 % increase compared to the control). Total phenols, total flavonoids, and antioxidant activity of the leaves and flowers were increased significantly by the application of HA and FA in the field and greenhouse conditions. The highest total phenolic contents of the leaves in the field and greenhouse were obtained from HA treated plants at 5 and 15 kg ha−1, which were 59 and 57 % more than the control, respectively. Also, the N, P, and K content of leaf were increased with the application of both HA and FA. Overall, the application of HA or FA had the most positive effects on improving the growth and antioxidant activity of yarrow, especially in the field conditions.