'Use your common sense and don't blindly follow advice'

His job as a WUR researcher on an experimental farm has made onion grower David de Wit critical of his own cultivation methods. If it is possible with less, then experiments are carried out. He explicitly does not cut back on other factors. For David and his father, the best onion quality is paramount.

The following will follow during the 2024 growing season Boerenbusiness Crop tour another ten plots of onions. From sowing to harvest, the participating arable farmers take us through the cultivation and decisions they make during the season. In this series of interviews we each get to know one grower, his company, vision and strategy. This interview is with onion grower David de Wit.

Together with his father, David de Wit carries out the work on the arable farm. In addition to working on the farm, he can often be found on an experimental farm where he has another job. That gives him a lot in terms of knowledge. "My father is the main entrepreneur and contributes most to the arable farm. In addition to my work on the farm, I can be found four days a week at an experimental farm nearby. During the busy periods I try to be at home more. My job at the experimental farm offers a lot of flexibility and I learn a lot from my colleagues. It is very valuable to work in two places in this way. It broadens my thinking and teaches me to look at certain decisions in agriculture in a broader way."

The Crop tour plot that Boerenbusiness follows is a plot of approximately five hectares of clay soil with 45% siltability. Wheat was grown as a preliminary crop on this plot. “We plowed and harrowed this plot in September to level it,” explains David. The onions were sown on this plot at the end of April. David only spread polysulphate and carried out a glyphosate spray. "The Rockito variety has been sown on this plot. We are also conducting a trial on this plot with the HyRoad variety. We are curious about the performance of this onion variety on our soil type. I can never properly deduce the results from the variety brochures. Often These varieties have been tested on a different soil type and with a different management. I would like to experience it myself. That is something we have been doing for a long time." De Wit is satisfied with the Rockito onions, just like his customers. "Another variety must really have added value if we want to switch."

Good first time
The onions are sown on 1,50m beds by a contractor. De Wit does the lifting and loading with two colleagues. "For us, this is an affordable way to harvest when we want. We often harvest the onions earlier than most growers in the area. Because we manage the machines ourselves, we do not have to wait for a contractor. We often harvest when the plant is still a bit green, while many growers wait for the last kilo. This year we use primed seed, which we tried for the first time two years ago. Then I saw no significant difference in emergence time techniques are improving and many growers are switching to primed seed. Uniform emergence is essential for good cultivation, especially because cultivation is becoming increasingly challenging. That is why we are opting for primed seed again this year. Hence the pre-treatment. With primed seed, everything has to be done right the first time and that is a challenge on heavy soil." The onions are stored loose in the ten-year-old storage shed, on a slatted floor. "Depending on the quality, we sell sooner or later. Storage until May is possible."

Substance use
De Wit tries to only use soil herbicides and hardly any contact agents. "Last year we hoeed to open up the soil after intense rain showers. Combining hoeing and the use of soil herbicides is challenging, because they counteract each other somewhat. By using almost no contact agents, we see slightly more weeds in our crop. This means we have more manual work. This is preferable to additional spraying." When it comes to insecticides, David pays particular attention to thrips. This means irrigating on time to maintain growth. "This way, spraying insecticides can be postponed for a very long time. As far as fungicides are concerned, it is alternated within a weekly schedule. So far we have never really seen any diseases in the onions, so we think this approach works well."

Critical of mildew spraying in onions
De Wit gains important experience at the experimental farm. "If I look at the current research, much less product should be needed. I think the BOS system for onions, for example, is weak. I hardly look at it. The system sometimes indicates after two or three days that I need to use it again. In my opinion, that is not the solution. It is important to keep your wits about you and not blindly rely on advice. Mildew is very difficult to predict made for mildew and have also seen years of high pressure. I wonder whether an increasingly shorter interval is the solution. That does not fit the future picture for our sector. Something that does need to be improved works well."

The polysulphate is now on the plot. Phosphate is applied in the row during sowing. After attendance we give a small starting gift of KAS, then again KAS and then NK16-30. "We do not use a high level of fertilization," says De Wit. "We aim for a maximum of 140 kilos of nitrogen, depending on the season and crop development. Sprinkling more can yield more gross kilos, but at the expense of quality. Creating healthy foliage is of the utmost importance. The yield will then follow automatically. Water is at least as important. We never give more than 15mm at a time and tend to use shorter intervals. This way the soil remains nice and moist and has good root penetration. Fortunately, we have good quality surface soil spring water. Salt is not a problem, but I still check the EC value regularly during the season. It is important to understand and know what you are doing."

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