First tests with drip irrigation promising CULTIVATION AND TECHNIQUE A lthough it takes at least five weeks before seed potato grower Foppe-Jan Dijkstra from the Dutch village of Aduarderzijl starts harvesting his first-year mini tuber strains, he’s rather curious about what’s already there. But he’s even more curious about the possible difference between the ridges with drip irrigation and the rows without the black perforated pipe system. He lifts a plant from each row and puts the tubers side by side. He’s pleasantly surprised about what he sees. The number is the same for both, seven tubers. That’s not uncommon. ‘In the dry spring of 2010, we harvested 3 to 4 tubers per mini tubers without irrigation. Three, that’s really bad.’ But what does surprise Dijkstra is the difference in grading. The crop results from under the drip tube are very even but those from the row without irrigation are highly varied. ‘I wasn’t expecting this. Contrary to the rest of the country, it has rained regularly here in the northern part of the province of Groningen. A shower of 20 millimetres here and there should have been enough.’ If you look at the overall weight, the yield of both plants won’t differ too much, Dijkstra thinks. An even grading, however, is more important for the seed potato grower. At first glance, it seems that the regular 1 to 2 millimetres of water from the drip tube have also brought regular growth. It’s very important that there’s water around the tuber setting. This ensures regular growth right from the time of initiation. In addition, that’s when you reduce infection by Streptomyces, or common scab, according to the seed potato grower. Mini tubers need moisture Dijkstra has been working hard with drip irrigation for some years now. You can take that literally, because the water system requires quite a bit of extra work. For that reason, he’s keeping the acreage with drip irrigation limited for now. At the moment, he’s growing a secondary crop from mini tubers on only half a hectare. The drip tubes are high in the ridge with this crop. ‘You shouldn’t plant mini tubers too deep, because a mini-tuber isn’t so vigorous. But tubers that are high in the ridge have the disadvantage that they quickly lack water in dry weather. This is why a drip tube high in the ridge is the best spot for this crop. If you add up expensive planting stock and a greater likelihood of a lack of water, the investment costs for drip irrigation are soon profitable for a crop like this’, according to Dijkstra. But he tries to keep the costs under control as far as possible. For example, the seed potato grower uses irrigation tubes that last a few years. ‘Heavier tubing lasts longer,’ says Van der Meij who has supplied the tubing on behalf of Netafim in Maasdijk. He cannot afFord to have any leakages during the initiation period of his strains. ‘That can give problems with disease.’ The seed potato grower uses tap water that he stockpiles in a tank in his yard. This tank can hold 20,000 litres of water. Yield 10 to 25 percent higher Dijkstra uses a relatively small pump for the drip irrigation. ‘This reduces the purchasing costs and the subsequent energy consumption.’ In order to water the whole plot evenly, he has divided it into 4 sections of 12 ridges. The sections are switched on one after the other with 20 to 25 minute intervals. This season, he has added fertiliser for the first time. First, in four applications of 30 litres a week, he gave Yara’s fluid nitrogen/phosphate fertiliser to the seed. In total, this top dressing consisted of 11 kilograms of nitrogen per hectare and 34 kilograms of phosphate. He later added an application with calcium/nitrogen/potassium fertiliser for the necessary cell growth and sturdiness of the tubers. Dijkstra can’t give an exact costbenefit calculation yet. He doesn’t yet know what the results of ‘fertigation’, the application of fertiliser via drip irrigation, will provide. It saves work and fertiliser, but the special fertigation fertiliser is also more expensive. Experience from recent years At the recommendation of irrigation expert Pieter van der Meij (l) of Netafim in Maasdijk, Foppe-Jan Dijkstra (r) uses thicker drip tubes that last longer. The crop results from under the drip tube are very even, but those from the row without irrigation are highly varied. 30 Potato World 2016 • number 1 Pagina 29
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