Effect of irrigation and bio-fertilizers on morphological and bio-chemical traits of milk thistle

The milk thistle plant strengthens the body’s immune system and is one of the top-selling medicinal plants in the world in terms of turnover. Considering the water crisis in Iran and especially in the northwest of Iran, which has led to the drying up of Lake Urmia, the cultivation of crops with low water requirements is considered important under the conditions of water scarcity. The cultivation of medicinal plants will solve the environmental problems of the region, change the cropping pattern from high-consumption to low-consumption crops, increase farmers’ income and ultimately improve the living conditions of farmers in the region. Given the significance of milk thistle, an experiment was conducted to assess the effect of irrigation type and biofertilizers on its seed yield, oil yield, and fatty acids. So, a split-plot experiment was conducted in Miandoab County at the south of West Azerbaijan province, Iran in 2016–2017 based on a randomized complete block design with 10 treatments and three replications. The main plot was assigned to irrigation regime (at two levels of full irrigation and no irrigation) and the sub-plot to biofertilizer (at five levels of control, nitrogen biofertilizer, phosphorus biofertilizer, potash biofertilizer, and NPK biofertilizer). Based on the results, the interaction of irrigation × biofertilizer was significant for biological yield, capitule number, and DPPH radical scavenging at the P < 0.01 probability level and for seed yield per plant and plant height at the P < 0.05 probability level. But, this interaction was insignificant for the other traits including harvest index, crown diameter, branch number, oil yield, phenol and flavonoid content, superoxide radical scavenging, nitric oxide radical scavenging, and chain breaking. In addition, it was found that most morphological and biochemical traits of the thistles were affected by irrigation and biofertilizers so that the biofertilizers improved them versus the control. Given the significant role of biofertilizers in the development of sustainable agriculture, they can be a good candidate in case there is a need for nutrient supplements for this plant. Under drought stress conditions, the combination of bio-fertilizers (NPK(b)) and irrigation helps the plant to tolerate drought stress easily and also improves the medicinal properties of the plant.