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A long hot summer.

November 2018

In North western Europe we have had one of the of the warmest driest summers ever. When you are on a holiday and you like to spent some time on the beach it is exactly the weather you want. When you are a potato farmer, you may have second thoughts about this kind of weather.

It is November now, potato harvests have been finished and most potatoes are sold or stored in the barn. It is time to wrap up this season and draw some conclusions for the future. First let’s overview the weather during the growing season. First sunshine, in the Netherlands we have had 25 % more sun hours than normal, 785 in 2018 compared to 608 on average. Then temperature, the average temperature was about 11 percent higher than normal, 18,9 °C versus 17.0 °C. Then rainfall and evaporation, in a normal summer we get about 225 mm of rain, this summer it was less than half of this amount, about 105 mm. And finally the precipitation deficit at the end of august was around 300mm.
All impressive numbers, how did this affect our potato crops and yields. Potentially production could be very high because of the high incoming radiation. The average temperature was not a problem for crop growth, but we had some heat spells with temperatures above 30°C resulting in reduction of crop growth and deterioration of the foliage. The biggest problem was the lack of rain in combination with the high evaporative demand leading to severe drought stress.
Effects on the crops differed depending on purpose, soil type, availability of irrigation water and grower. On average the yield was about 30% lower than average. Crops for French frying industry had problems with tuber size, low dry matter and second growth. Early seed tuber crops have very low yield and sizes and starch potatoes have also problems with low yield and dry matter. When you look around, you will find also growers with normal to good yields. They often had access to good irrigation water and/or had water retaining soils. The overall result is a shortage of potatoes for the industry and seed potato supply chain.
Currently most potato crops in North-Western Europe are rain-fed, sometimes supported with an occasional water gift during a dry spell. In the future this will not be enough because climate scientists tell us that we should expect more of those hot dry summers. When we want to continue growing potatoes, irrigation is inevitable and farmers have to have access to irrigation water. This was not always the case last summer, especially on de higher sandy soils.
Future potato production in North western Europe will ask extra attention to water management on and around the farm. It means that water must be retained and stored during wet periods using under and above ground water basins. Secondly during the growing season irrigation has to be more efficient, nowadays sometimes half of the irrigation water evaporates before it can be used by the crop. The result will be higher production costs, but lower risks on shortage in the supply chains. For a healthy sector in the future the extra costs and efforts should be rewarded. Only then can everyone enjoy these long hot summers.

Dr. Ir. Peter Kooman
Professor Potato supply chain and sector innovation
CAH Vilentum University of Applied Sciences


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