Evaluation of common bean (Phaseolus vulgaris L.) seed yield and quali-quantitative production of the essential oils from fennel (Foeniculum vulgare Mill.) and dragonhead (Dracocephalum moldavica L.) in intercropping system under humic acid application

In order to evaluate the effectiveness of fennel/common bean/dragonhead intercropping and humic acid application on common bean (Phaseolus vulgaris L.) seed yield and the quali-quantitative production of fennel (Foeniculum vulgare Mill.) and dragonhead (Dracocephalum moldavica L.) essential oils (EOs), a 2-year field experiment was carried out with a factorial design based on randomized complete block design with three replications. The first factor was given by 10 different cropping patterns including common bean monoculture, fennel monoculture, dragonhead monoculture and different intercropping ratios, 1:1:1, 1:2:1, 1:3:1, 2:1:2, 2:2:2, 2:3:2, 2:4:2 (fennel: common bean: dragonhead), whereas the second factor was represented by usage or not of humic acid (organic manure). The results demonstrated that the highest seed yield of fennel and common bean and biological yield of dragonhead were recorded in the monoculture of each plant. Application of humic acid increased the seed yield productivity of common bean and fennel and biological yield of dragonhead compared with control (i.e. no application of humic acid) by 10, 16 and 7%, respectively. Also, concentrations of N, P, K, Ca and Mg in most of intercropping patterns increased over the monocultures. Additionally, the different intercropping patterns and application of humic acid improved the content of (E)-anethole, fenchone and limonene in fennel EO and those of geranial, neral and neryl acetate in dragonhead EO, over the control. Overall, intercropping of fennel and dragonhead with common bean under humic acid application could improve the EO quality and quantity of the mentioned medicinal and aromatic herbs and can be recommended to farmers as an alternative, sustainable and cleaner cultural system.