Assessing the effects of water stress and bio-organic fertilizers on English and French Lavandula species in different locations

A study was conducted utilizing a factorial split-plot design within complete randomized blocks to evaluate the effects of water stress (at 95±5, 75±5, 50±5, and 25±5% of the field capacity (FC)) and various fertilizer sources (Azotobacter-Psedomonas Bacterial (APB), arbuscular mycorrhizal fungi (AMFs), and biochar (BI), applied individually and in combination, along with a control treatment on the two species of lavender (French and English) in two distinct climates (Fars and Hamedan) in Iran. The results revealed that severe water deficit stress reduced the growth, yield, and essential oil content in both lavender species. APB+AMFs+BI and APB+BI led to the highest flower yield for French lavender in Fars and Hamedan while subjected to well-watered conditions. The essential oil yield significantly decreased in both experimental regions under 25% FC. Employing APB+BI under 75 and 50% FC treatments led to the highest essential oil content (4.23 and 1.56%, respectively) in English lavender. Linalool showed the highest average (22.46 to 30.06%) in both species. French and English lavender in Fars showed significant differences in fatty acid compositions, but no such differences were reported in Hamedan. APB+BI emerged as the most effective fertilizer combination in terms of total fatty acids and rank index. Simultaneous use of bio-organic fertilizers yielded appropriate results under water-deficient conditions. Finally, the study underscored the strong correlation between climatic parameters such as rainfall and temperature, as well as the efficacy of different fertilizer sources, emphasizing that climatic condition and plant species can significantly impact the effectiveness of fertilizer use.