Production of sage, oregano and rosemary under shading conditions and the effects of light on growth and essential oil properties

Intercropping and agroforestry systems provide sustainable land and resource use efficiency, however, shading conditions generated by the base crop or tree cover is a restricting factor on the growth of the intercrop and productivity of the system. Hence, a two-year field experiment was carried out to assess the yield, essential oil properties, morphological changes, and anatomical adaptation of the shade-exposed sage (Salvia officinalis L.), oregano (Origanum onites L.) and rosemary (Rosmarinus officinalis L.) plants. Plant height, leaf area, chlorophyll content, herbage yield, essential oil content and biochemical profile of the selected species were comparatively examined under open-field, 40% and 75% shading conditions. Initially, after the seedlings were transplanted to the field, a horizontal growth of shaded plants, resulted in lower plant height, then, after the plants covered the soil surface, vertical growth was observed. Overall drug herbage yield decreased by 65% due to the shading treatments in the first year whereas rosemary, sage and oregano had 20.9%, 25.3% and 40.3% lower yields respectively in the second year. Average essential oil content of low-light exposed plants increased by 23% and 41% first and second year of the experiment, respectively. A negative linear relation between a-thujone content in essential oil of sage and shading level was recorded while in contrast, carvacrol content of oregano essential oil increased by shade treatment. The results concluded that herbage yield and quality properties of shaded plants were promising, especially after the first year, considering their potential in intercropping and agroforestry systems. Since the current study represented the results for artificial shading conditions, the tree-based intercropping studies needed to be performed with these species for the final conclusion.