Assessing Nitrogen-Fixing Bacteria and Mineral Nitrogen Fertilization Regimes for Boosting Growth, Photosynthesis, and Essential Oil Production of Clary Sage (Salvia sclarea L.)

Abstract

Clary sage (Salvia sclarea L.) is a valuable medicinal biennial herb, and its oil is characterized by an ambergris scent and finds uses as a spice and a vital ingredient of cosmeceutical products such as perfumes, soaps, cosmetics, and aromatherapy. However, its scale of production has remained far below its potential, especially owing to inappropriate plant nutrition management. To bridge this research gap, a field experiment was conducted to comparatively assess the mineral nitrogen (N) fertilizer doses (120 and 60 kg N ha-1) and nitrogen-fixing bacteria (NFB, including azotobacter, chroococcum, and cyanobacteria) for boosting the growth, yield, oil content, and primary essential oil composition of clary sage plants. The results revealed that the higher dose of N applied in conjunction with azotobacter and cyanobacteria recorded the highest concentration of macro and micronutrients in clary sage plants, except for iron content. Additionally, the same treatment exhibited unmatched photosynthetic efficiency as demonstrated by significantly higher NDVI (normalized difference vegetation index), SPAD (soil plant analysis development), and chlorophyll fluorescence values, which resulted in the highest leaf area and shoot dry weight of plants. Moreover, this treatment also remained superior by recording the maximum concentration of essential oils, particularly alpha-pinene, camphene, beta-pinene, limonene, and linalool contents. Thus, clary sage production with superior growth potential, higher photosynthetic activity, and essential oil productivity might be achieved with the co-application of mineral N fertilizer (120 kg ha-1) and NFB (Azotobacter and Cyanobacteria).