Solutions and washing times of phenolic foam in lettuce seedlings production

The main characteristics of the phenolic foam are inherent to a substrate of excellent quality such as sterility, excellent aeration and high load-bearing capacity. However, as it comes from a phenolic resin, the foam has some residues that can affect the development of plants. Thus, this work aimed to evaluate different treatments for washing phenolic foam under the germination and initial growth of lettuce seedlings in two immersion times. The experimental design was completely randomized (DIC), in a 5x2 factorial scheme, containing four replications with 56 plants per plot. Each repetition was composed of a phenolic foam board. The experimental factors consisted of different substances: caustic soda (NaOH), pint lime (CaOH2), citric acid (C6H8O7), vinegar (CH3COOH) and water in solution with distilled water, and two immersion times (30 minutes and 18 hours). For the witness treatment, there was no immersion. After 18-hour immersion, the treatment with citric acid presented the best development for height and biomass in the lettuce seedlings. On the other hand, the 4,0% vinegar pretreatment was not considered viable for phenolic foam for any of the times analysed. There was a significant decrease in seedling biomass when no treatment in the foam was carried out before sowing the lettuce seeds. The caustic soda presented lower results for emergence speed index, fresh aerial biomass, height and number of leaves for the 18-hour immersion compared to the 30-minute immersion.