Effects of different levels of humic acid and planting density on antioxidant activity and biochemical properties of (Trigonella foenum- graecum L.)

Fenugreek (Trigonellafoenum- graecum L.) is one of the significant medicinal plants and application of organic materials is very important for achieving maximum yields of that. In this study, the effects of applications of humic acid and planting density on biochemical characteristics of fenugreek were evaluated under field conditions. Treatments were of three levels of humic acid (0.5 and 10 kg ha-1) and two plant density (25 and 50 plants/m2). This experiment was carried out as factorial based on randomized completely block design with three replications in research farm of University of Birjand, Iran, during growing season 2016.The leaves` antioxidant compounds (antioxidant activity, total phenol and anthocyanin) were recorded at flowering stage. The results were showed that humic acid had significant effect on most biochemical characteristics(antioxidant activity, flavonoid content, total phenol and carbohydrate). The highest of antioxidant activity (64. 67%) and carbohydrate (6.73 mg/g) were observed in 10 kg/ha humicacid, while the lowest antioxidant activity (50.03%) and carbohydrate (3.45 mg/g) were recorded in control. Also, the humic acid uses significantly increased photosynthetic pigments (total chlorophyll, a, b and carotenoids). The highest and the lowest total chlorophyll content were observed (4.51 mg /g) in 10 kg/ha humic acid andcontrol (3.18 mg/g), respectively. Based on the results, the highest flavonoid content (6.43 mg/g) was obtained in the plant density of 25 plants /m2, whereas the lowest flavonoid content (5.46 mg /g) was in planting density of 50 plants /m 2. There were significant differences in the total phenolic and flavonoid content due to interaction plant density and humic acid treatments, in which the highest amount of total phenolic content (42.07 mg/g) was observed in 10 kg/ha humic acid with the plant density of 25 plants /m2.and the lowest content was recorded (41.86 mg /g) in the control with density of 25 plants /m 2. According to the results, using 10 kg ha-1 of humic acid and planting density of 25 plants/ m2 had a significant role in increasing biochemical characteristics of fenugreek.