'Good storage starts with good drying'

With around 80% of the harvest behind the shelves, the majority of seed onions are currently being prepared for longer or shorter storage periods. "Proper storage starts with proper drying," says onion expert Kees Jacobs. "Take your time and ensure you have sufficient temperature sensors and a good RH meter. Then you'll know what you're doing."

"Most of it is in, but there are still quite a few onions scattered throughout the field in the swath," says expert Kees Jacobs. "Sporadic onions are even stuck. The fact that they're losing some color now isn't a problem. The soil layer will come off anyway. And for fields with a lot of fusarium, the forced stay in the swath even has advantages. The affected onions can now rot away nicely."

Jacobs points out the potential danger of bacterial disease: "Onions that have been affected by a late onion fly or bean fly outbreak are at a higher risk of bacterial disease in storage. The puncture holes are the entry points. You can't see it from the outside, but if there's bacterial disease in the batch, it reveals itself with a pungent stench. So monitor the batch carefully."

Drying takes time
Jacobs estimates that the bulk of the onions will still be in the drying phase. "I think drying will be a bit easier than in previous years because the onions arrived relatively dry after a good period in the fields. And we have far fewer thick-necked onions. That also saves a lot of moisture."

When drying, Jacobs says it's important to take your time. "All the moisture has to pass through the thin neck, and that simply takes time. Gradual drying with air at 20 to 22 degrees Celsius is, in my opinion, the best method. This also prevents water spots from forming." To properly monitor the drying process, Jacobs recommends inserting a temperature probe into the pile in several places. "Temperature differences often indicate moisture differences, so that tells you more." 

An RH meter is also indispensable in a well-equipped onion storage facility, says the onion expert. "You have to continue drying until the RH at the top of the pile has dropped to 60% to 65%. You can't estimate that with a wet thumb. It usually takes about two weeks to reach that value. And after that, you have to keep monitoring the RH meter closely. A slow increase in RH is normal, but if it rises substantially above 80, you have to adjust. And then you definitely need a heater, because by then it will be late September, early October." Only when the batch has a stable RH of 80% for an extended period is it time to start cooling. Jacobs: "If you maintain a cooling rate of 1,5 degrees per week, you'll be keeping pace with the season and have the opportunity to dry again along the way if necessary."

Did the MH succeed?
Jacobs also wants to draw attention to the MH situation: "Because the onions deteriorated so rapidly at the end, as a grower you have to ask yourself if there was still active sap flow for at least two weeks after the MH spraying. If not, there's a chance the onions will germinate sooner. I'll come back to that in October." 

Coordinate mechanization well!
Kees Jacobs observes along the road that agricultural tippers are becoming increasingly larger and, above all, taller. "You see that older onion loaders, in particular, can no longer reach the bottom of the tipper. As a result, the drop heights are greater than the onion would like. I use this as an example of a harvesting line that isn't optimally aligned. When you're advancing in mechanization, it's important that the sizes and capacities of the machines are properly coordinated."