Seed potato grower Klaas Jan Jensma from Hijum puts his heart and soul into the production of quality seed potatoes. And once it is ready for delivery, he prefers to send it – perhaps surprisingly – in big bags to the consumer grower. "That is a nicer and cleaner journey for the tuber." We asked Jensma what his approach to good seed potatoes looks like.
In one of Klaas Jan Jensma's barns hangs a sign with the motto: 'Delivering quality costs money. But not delivering quality costs a fortune'. It characterises the attitude of the Frisian seed potato grower who annually plants around 80 hectares of the specialist crop with his employees. At Jensma's company, the care for quality already starts with the handling of his own seed potatoes. He grows all his seed potatoes from mini tubers and prepares his batches for his own propagation with a sophisticated combination of storage temperatures and Talent treatment (see box). Jensma: "Then by the end of March, beginning of April I have tubers that are sufficiently activated and can produce many stems." When planted, the tubers are given double protection against soil fungi and liquid phosphate and a slow-release liquid nitrogen fertiliser as food. Aphid control begins soon after emergence and not much later phytophthora agents are also added to the tank of Jensma's air-supported sprayer.
Limiting fall heights
During harvesting, Jensma ensures that the mother tubers remain on the land – he even exchanged his 4-row self-propelled harvester for a trailed bunker harvester with a reading belt – and ensures minimal drop heights at all points in the harvest line. "The support rollers under the conveyor belts in particular cause considerable impacts, which you have to avoid," the seed potato grower knows. All the seed potatoes go into crates that are placed directly in front of the drying wall. The seed potatoes that find their way to destinations in the Netherlands and North-West Europe in the spring are stored in a computer-controlled draught shed at 7 to 8 degrees until sorting. Before sorting, they are heated to around 10 degrees to prevent blue and then they go into the cold store until delivery. Just before delivery, Jensma reads all his seed potatoes for a second time. "I want to be sure that I am transporting good seed potatoes. After all, my grower number is on the card."
Bigbag is favorite
For transport to the consumer grower, the big bag is Jensma's favourite method. "In a big bag, the tuber has a better journey", is Jensma's conviction. "A big bag is always clean and the potatoes fall less high than in a bottom unloader. I am happy to do the extra work for that. And a big bag fits exactly in a cubic crate, so you don't have to do any extra work at the recipient." The recipient must then quickly convert the seed potatoes into crates, because a big bag is clearly less suitable for long-term storage, Jensma also believes. After receipt, it is important that the crates are well ventilated and stored cool. "Anyone who receives seed potatoes in November can store them at 3 degrees without any problems", says the seed potato grower. "That helps to prevent long sprouts. When receiving in February, I advise to store between 4 and 6 degrees. But even if you cannot cool, the seed potatoes can easily be kept in condition for a month. And if the sprouts become too long, you can turn the boxes once."
Keeping origins separate
Jensma concludes his story with two sincere tips for the receiving growers. "Always check the seed potatoes very carefully upon receipt. Whether it is in a bottom unloader or a big bag, it does not matter. It is a living product and something can always go wrong. And if you work with seed potatoes from different origins, keep them separate and note what you have planted where. Then you can find out which batch it was in case of any problems."
Also watch the video of Klaas Jan
This is how Jensma prepares his own seed potatoes
The seed potatoes that Klaas Jan Jensma plants on his own farm the following spring, are stored for about a month after the wound has healed at 3 degrees. This causes the tuber to saccharify and that sugar is fuel for the sprouts. In mid-November, the tubers are given a heat boost to get the germination going and then the seed potatoes are stored in the Talent at a temperature of 7 to 8 degrees. The Talent burns off the sprouts and in doing so breaks the top sprout dominance. This causes more sprouts and therefore more stems and tubers to develop.