Various risks lurk in onion cultivation during the period from sowing to emergence. Onion experts Kees Jacobs and Michiel van Mol discuss what you should and should not do to ensure a smooth and even turnout. Because that is where the basis for a high yield of good quality lies. "The onion must be able to go through in one go."
"Seed sales remain at a reasonable level with us, maybe even a small plus, but we also see and hear that growers are still unsure whether they will sow onions and how much." According to the Syngenta onion experts In addition to the rising costs and looming problems in disease control, there are also a few bright spots to be found. Jacobs: "With the current unrest in the world, food is becoming more important. And in Poland, a 50% decline is expected in vegetable crops, including onions." Continuity in cultivation is best, thinks Van Mol: "If you are an onion grower, then stay an onion grower. Have faith in the market and stick to the cultivation measures whose effectiveness has been established."
Cold and wet surface
Patience is perhaps the most important cultivation measure at the start of the season, according to Jacobs. "It has dried up a lot lately, but be careful. The structure is fragile because we had little frost and the soil at the bottom is often still wet, especially on the clay. That means little bearing capacity and therefore a chance of compaction. And the soil is empty. many places are still too cold. A soil temperature of at least 10 degrees is required for a smooth germination and emergence." Van Mol continues: "If the soil is too cold, the seedling will take longer to travel. And that gives the bean fly a better chance to strike." Waiting a little longer for cold soils is also not a problem, he thinks: "Such soil often provides sufficient moisture. So if you wait for the right soil temperature, the seed can continue smoothly."
Playing with seed density
According to the onion experts, the optimum sowing depth is 2 centimetres, but such a thin layer of loose soil is difficult to achieve in practice, they know. "Usually this only works if you have already done a pre-treatment immediately after plowing or in the winter. But if you sow 3 centimeters deep, it usually works out well, as long as the seed is on solid ground." In case of doubt about the connection with the substrate, rolling should be considered. "But do that as soon as possible after sowing."
An irregular emergence or a stand that is too thin increases the risk of quality problems in the end product, says Jacobs. "Unfortunately, you could see that in many places last season. Thick necks and bolts are the result. That is why we always recommend a minimum of 3,6 units per hectare. Then you are covered for a little loss, because there is always that. And if the If the conditions are moderate, sow a little more. This is quite normal in the cultivation of winter wheat, but I don't see it enough with onions."
Enough kali important
Problems with fertilization are not only due to high prices, but also to availability. "I know growers who are still waiting for their potash 60", says van Mol. It is better for them to wait until the plants are well above the surface. Otherwise you will get salt damage." The onion experts are clear about the gift: "An onion should have at least as much potassium as a potato. So at least 250 kilos of pure. The mineral is important for good hardness and for bridging dry periods." Jacobs and Van Mol warn against an excessive nitrogen supply. "That can have a negative effect on skin resistance. For fast-growing varieties, keep it to a maximum of 150 kilos; with slower-growing varieties, an additional 20 kilos can be added." If you have space, you can consider a phosphate starting dose. "Think about 50 kilos wide or 10 to 12 kilos in a row." For N and K, the onion experts advise to adjust the dose in give two or three parts."
Crust cracking
No one knows whether it will happen this season, but crust formation can also hinder a smooth emergence. "The best solution is to irrigate, preferably with a fine nozzle," says Jacobs. "If that doesn't work, you can try to crack the crust. All kinds of solutions have been devised in recent years. It is important that the soil breaks into small plates. And don't wait too long." He does have a tip for the latter. "The trick with the glass plate still works well. The onions underneath come a little earlier because it is warmer and more humid. That gives you a good grip for the moment of burning off or breaking the crust."