"When storing onions control RH instead of temperature"

When drying onions in storage, many onion growers choose a temperature of 20°C or above 30°C. Huub Kasius of Agrovent, however, called for the relative humidity (RH) to be used as a starting point instead of temperature at the Themadag Uien van Landbouwbeurs Noord- en Centraal Nederland (LNCN) (Onion theme day of North and Ventral Holland Agricultural Fair) in Dronten.

'When controlling an RH of less than 65 percent instead of just the temperature much can be achieved. There is now fear of drying at a temperature between 22 and 26°C, but this isn't damaging if the RV remains under 65%. But this is hardly controlled, perhaps due to cost consideration, but because the drying time is shorter it doesn't take more energy."

Kasius pointed out that the storage result depends almost completely on the drying process in the first weeks. He pointed out that there are a lot of onions in storage at the moment that aren't sharp. "Check the storage yourself and don't just trust the computer. It controls the settings, but not the result. A farmer checks his cows every day too. A storage warehouse isn't a hospital, but it is a hotel."

The reason for keeping the temperature above 30⁰C is a good one, according to Huub, as the drying time is considerably shorter, the growth of fungus such as neck rot is limited and the RH goes towards 50%, which causes the neck to close even faster. "As long as the neck isn't closed, there is little danger of drying out the layers too much in most cases. When the neck is closed, the RH can go back up."

The optimal situation would be to dry with an RH under 65% independent of weather and outside air. In contrast to fruit and vegetables for example, arable farming is one of the few sectors without conditioned storage for the entire process. This might go well for three out of five years, but the changing climate will cause more risky years like 2015.

Kasius showed the opportunities of a closed, conditioned storage, which works as a condensation dryer. "This offers the possibility to dry after at low temperatures after cooling, has no gas burning and is energy efficient when it comes to winning back heat, which can be combined with solar panels. "But if investing in drying in a closed storage isn't an option yet: Much can be achieved with the knowledge of drying principles - control RH <65% instead of just temperature. So put those heaters high enough, even if it's warm outside."

For more information:
Huub Kasius
Agrovent
Mob; 0031 (0) 6-309915400031 (0) 6-30991540
kasius@agrovent.nl
www.agrovent.nl