A field trial was carried out during 2018/2019 and 2019/2020 seasons at the Experimental Farm of Faculty of Agriculture, Assiut University to study the effect of foliar humic acid application at the concentrations of 0 (control), 200 and 400 ppm three times, monthly interval on growth, fruit yield, and essential oil yield and its composition of caraway (Carum carvi L.) plant.
The results indicated that humic acid treatments improved the vegetative growth characteristics (plant height, branch number per plant and plant dry weight), fruit measurements (umbel number, 1000-seed weight and seed yield) and essential oil parameters (oil percentage, oil yield and oil constituents) in comparison with control plant (without humic acid). However, a rate of 400 ppm was more effective than the level of 200 ppm in this regard.
Seeds of plants received 400 ppm showed the highest contents of total proein, total carbohydrates, total phenolics, ascorbic acid (vitamin C) and thiamine (vitamin B₁). In contrast, these seeds contained the lowest levels of nitrate and nitrite. These findings were closely correlated with increasing 1000-seed weight showing better quality.
Chemical analysis of caraway leaves cleared that the maximum contents of nitrogen, phosphorus, potassium, and pigment were occurred by humic acid at 400 ppm resulting in significant increases compared to 200 ppm level in most cases. It was found a positive relationship between the highest contents of leaf N, P and K and the improvement of vegetative growth and fruit characteristics, consequently increase of seed production.