3.2 Measurements, sampling and analyses

4.2 Development of seedlings

On 02.11.2020 were seeds of tomatoes and sweet pepper sown in small rockwool plugs (plug size: 2 cm diameter x 2,7 cm high, Grodan® Plantop Plug). On 09.11.2020 were seeds of cucumbers sown in rockwool cubes (cube size: 10 cm long x 10 cm wide x 6,5 cm high, Grodan® Delta). Seeds were covered with plastic until germination and kept under 23°C. Tomato seedlings were transplanted in rockwool cubes (cube size: 10 cm long x 10 cm wide x 6,5 cm high, Grodan® Delta) one week after sowing and sweet pepper seedlings two weeks after sowing. As needed was the space between cubes increased in the row to one cube between cubes and one cube between rows. Later was the distance increased in the row to two cubes between cubes and one and a half cube between rows. Cubes were placed in the middle table of each chamber. Seedling production of tomatoes took six weeks (until 14.12.2020), of sweet pepper ten weeks (until 11.01.2021) and of cucumbers five weeks (until 14.12.2020). At the end of the seedling production had tomatoes developed one cluster, sweet pepper was dividing the stem into two tops and started to flower and cucumbers had developed six leaves. The temperature was set on 20°C during day and 20°C during night. Ventilation started at 22°C. The underheat was set to 35°C. No carbon dioxide was provided. Installed was a misting system. Humidity was set to 70 %. To be able to decrease differences in the air temperature resulting of the high radiation heat under HPS lights, was the LED treatment set up next to a chamber that was characterized by high temperatures. Seedlings were watered on a regular basis. Seedlings received standard nutrition consisting of calcium nitrate and “YaraTeraTM KristalonTM Scarlet” (N 7,5 %, P2O5 12 %, K2O 36 %, MgO 4,5 %, SO3 10 %, B 0,027 %, Cu 0,004 %, Fe 0,075 %, Mn 0,06 %, Mo 0,004 %, Zn 0,027 %) as needed.