Intercropping and fertilizer type impact seed productivity and secondary metabolites of dragon's head and fenugreek

Abstract

Intercropping of medicinal plants is a relatively new practice to enhance sustainability in medicinal plant production. However, only a few studies paid attention to response of secondary metabolites of medicinal plants to organic fertilizers and bio-fertilizers in intercropping system. Here, we evaluated the effects of different fertilizer types (bacterial fertilizer, mycorrhizal fungi and vermicompost) plus an unfertilized control, in factorial combination with a monocrop or various intercropping ratios on seed and oil yields, root colonization, nutrient contents and secondary metabolites of dragon's head (DH) and fenugreek (F) in a two-year experiment. Organic and bio-fertilizers were effective in increasing the seed and fixed oil yields of dragon's head and fenugreek, essential oil of dragon's heads and the diosgenin and trigonelline content of fenugreek mainly due to enhanced nutrient uptake and root colonization. Across intercropping systems, bacterial and vermicompost fertilizers resulted in highest values for most parameters, followed by mycorrhizal and unfertilized control. Total land equivalent ratio (LER) for seed yield of DH and F was >1 in all comparisons, implying that intercropping always performed better than monocropping systems of both species. In the comparison among the intercropping systems, the highest seed, fixed and essential oil contents in dragon's head were attained with the 75DH:25F followed by the 60DH:40F intercropping ratios. The highest values of most secondary metabolites and oil compounds were obtained from the intercropping ratio of 60DH:40F with the bacterial biofertilizer. The main fatty acids in DH's oil were saturated palmitic acid and stearic acid and unsaturated oleic and linoleic acids. The main essential oil components of DH were thymol, carvacrol, spathulenol, and caryophyllene oxide. The major fatty acids of F were palmitic, linoleic, oleic, linolenic and stearic acids. The present research suggests that different intercropping system ratios with the application of organic fertilizers and biofertilizers represent an effective strategy to enhance the overall seed and oil yields and the secondary metabolites of dragon's heads and fenugreeks.