The effect of plant biostimulants on the macronutrient content and ion ratio of several lettuce (Lactuca sativa L.) cultivars grown in a plastic house

Plant biostimulants have been identified as one of the most important agronomic factors that scientists have been looking for in a range of natural sources over the last few decades. The purpose of these experiments was to see how plant biostimulants (Willow bark extract, Bistep, and the combination of Willow+Bistep (W+B)) affect macronutrient content and ion ratio in three lettuce cultivars (May King, Kobak, and Great Lakes) from 2019 to 2021. Willow bark extract was diluted to 3% and applied to the plants through irrigation with the amount of 50–60 mL plant⁻¹, whereas Bistep was sprayed every two weeks from transplanting in accordance with the manufacturer's recommendations at 0.05% with the amount of 20 mL plant⁻¹. The data demonstrate that over the grown seasons, the treatments W+B and Willow bark extract were the most effective biostimulants impacting macronutrient content and ion ratio, whereas Bistep was the least effective. In comparison to untreated plants, the amount of macronutrients (Ca²⁺, Mg²⁺, and P) in lettuce leaves rose by 18%, 13%, and 9%, respectively, in plants treated with W+B over a period of years, while, potassium (K⁺) significantly reduced by 15%. Sodium level, on the other hand, was significantly improved using plant biostimulants of Bistep, Willow and W+B by 33%, 57% and 72%, respectively. Ca²⁺ and Mg²⁺ levels in lettuce cultivars were substantially higher in the season of 2019 when the climate was cooler and the air humidity was higher, but Na⁺, K⁺, and P levels were higher in 2020 when the temperature was somewhat warmer and dryer. Among the lettuce cultivars, Great Lakes lettuce has a greater level of macronutrient content (Ca²⁺, Mg²⁺, Na⁺, and K⁺), however, Kobak contained much higher phosphorus (P) content at 301.41 (mg kg⁻¹ DM). Plant biostimulants enhanced the ion ratios of Na⁺: Ca²⁺ and Na⁺: Mg²⁺, but the only substantial improvement in Ca²⁺: P ratio was in plants treated with W+B from 2019 to 2021, particularly in the Kobak variety by 20%. Biostimulants, on the other hand, decreased the mass ratio of (K⁺+Na⁺): (Ca²⁺+Mg²⁺) in lettuce cultivars. Among plant biostimulants, Willow and the combination of W+B had the highest influence on nutritional absorption and ion ratio, although Bistep had the least. The macronutrient composition and ionic ratios of lettuce cultivars varied according to the cultivar differences and climate conditions. In our 3-year experiments, we discovered that the Great Lakes variety had a higher macronutrient content in the season of 2020, whereas the Kobak variety had a higher ion ratio.