Effects of different irrigation levels and varying doses of silicon applications on yield and some physiological parameters in lettuce cultivation

The study was repeated for two years to reduce the effects of water scarcity and drought stress in lettuce cultivation. The irrigation problem was created by applying 25% (I25), 50% (I50), 75% (I75) and 100% (I100) of the evaporation amounts formed in the class-A evaporation vessel. Si0 (0 kg ha–1), Si40 (40 kg ha–1), Si80 (80 kg ha–1) and Si120 (120 kg ha–1) silicon fertilisation was applied at four different doses. Head length, head diameter, head weight, root length, and leaf fresh and dry weight were measured in harvested plants. According to the data of 2020–2021, the best results in the effect of different doses of Si applications on plant head height, head diameter, head weight and root length at different irrigation levels were recorded from I75 × Si80, I75 × Si120, I100 × Si80, I100 × Si120 applications with the same severity level. While the Si40 dose gave good results at I75 and I100 irrigation levels, its effect decreased at I25 and I50 irrigation levels. At different irrigation levels where different doses of silicon were applied, I25 irrigation had the lowest leaf chlorophyll and relative moisture content and the most severe membrane damage, while I50 irrigation had a moderate effect. Leaf chlorophyll and moisture content increased, and membrane damage decreased in I75 × 80 kg ha–1 Si, I75 × 120 kg ha–1 Si, I100 × 80 kg ha–1 Si and I100 × 120 kg ha–1 Si applications. As a result, when the effects of the applications covering two years on plant growth and yield were evaluated, the most successful irrigation levels were determined as I75, I100, and the most successful silicon doses; were determined as 80 kg ha–1 and 120 kg ha–1.