RE SEARCH Cross planting gives more same-size tubers I n his field in the Frisian village of Waaxens, potato seed selector Durk Bierma explains how cross planting in a 90 cm wide ridge works. The idea behind this way of planting is that the plants are optimally distributed across the plot. By planting crossways in the wider ridge, Bierma plants 14 percent more seed potatoes. This requires an extra investment of 200 euros per hectare as compared to planting in 75 cm ridges. Bierma believes that producing the expected extra 10 percent will give him 1,000 euros of extra income per hectare. In theory, the new system seems to be successful. Big interim differences To check whether the expected surplus yield is basically correct, in the coming three years Bierma will grow the Carrera, Victoria and Innovator varieties on a 2-hectare plot on both 90 cm and the standard 75 cm ridges. The varieties have been chosen in consultation with HZPC, the Frisian trading company where Harm Steenhuis works as an agronomist. He tells us that the three varieties have distinct differences in growth and development. ‘We’re especially curious to see the influence of this cultivation method on the number and the green discolouration of the tubers’ Steenhuis explains. He tells us that the early Carrera variety grows high in the ridge as does the late Victoria variety. The mid-early Innovator variety grows lower in the ridge. After 90 growing days, the Innovator shows a 10-percent higher yield in the 90 cm ridge as compared to the 75 ridge. The Victoria is about the same and the Carrera is 20 percent lower. Better moisture supply The first readings done by Broekens Mechanisation showed that the moisture supply in the wider ridge was better as a result of which tuber initiation is expected to be more successful. Temperatures were also more constant than in the 75-cm ridges. The explanation is that the ridge warms up less during the day and dries out less at night. As far as selection is concerned, Bierma indicates that the higher number of stems per square metre gives a somewhat denser picture. ‘But you get quickly used to that’, the potato seed selector tells us. Neither Steenhuis nor Bierma want to draw final conclusions from this early trial lifting. It will take a few years before it becomes clear whether this method of growing seed potatoes really has an added value. For example, adjusting the machinery to 90 centimetres also costs money and it has yet to be proved whether this is outweighed by the advantages. ● Jaap Delleman In his field in the Frisian village of Waaxens, potato seed selector Durk Bierma explains how cross planting in a 90 cm wide ridge works. Potato World 2014 • number 3 35 Pagina 34

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