CULTIVATION AND TECHNOLOGY First experiences with Controlled Release Fertiliser in the cultivation of seed potatoes are promising ‘A gradual release of nitrogen ensures uniform crop development, better initiation and regular tuber growth’, says Roel Bloemert (r) of Everris. tions. You either apply too much and you get excessive haulm development, or it’s not enough and you end up with a low yield. A fertiliser that slowly releases its nitrogen over a period of three or four months would therefore be the perfect solution, the growers thought. Now, after three years of trials, this has proved to be the case. Coating with micropores How does CRF fertiliser work exactly? ‘You’ve got a granule with a little ball of nitrogen in the centre. The little ball of nitrogen is coated and protected. The coating holds micropores that allow moisture to pass. As a result, the fertiliser inside the coating dissolves, while the outside layer remains intact. The consequence of this process is a difference in osmotic pressure between the inside and the outside of the granule. Inside the coating, the fertiliser concentration is higher than outside, which means that the dissolved fertiliser is gradually pressed through the permeable coating. The thicker the coating, the slower the process and the longer the period in which the fertiliser is released. The type of coating also influences the level of permeability, which means that there are granules that have a time-release of two to three months and those that act for three to four months. For example, potato seed selectors prefer the 2 to 3 months granules, while seed potato propagators would rather use a 3 to 4 month granule. As already said, we’re talking about an NPK 38-0-0 here, which means that the granule contains 38 percent nitrogen. Furthermore, the granule contains sulphur. An application of sulphur is also welcome in a crop of seed potatoes, as sulphur deficiency in crops has increased in the Netherlands in recent years,’ Bloemert explains. Keep small granules intact The best time of applying is before or during planting or between planting and using the cultivator. ‘If you distribute the fertiliser in the field and are not able to plant or cultivate immediately, the special coating will prevent the nitrogen from evaporating. It’s important though that the relatively-small granules are kept intact. It’s therefore a good idea to maximise the broadcaster to 24 metres. It would be best to apply the fertiliser in bands during planting, thus avoiding damage to the granules, which will reach the root zone as closely as possible. A grower needn’t be afraid of salt damage, because Agrocote isn’t a fertiliser based on salt and is therefore safe for the root system. And the granules don’t harm the soil life, either. As soon as the seed potato growing season is over, the granule is Potato World 2014 • number 3 31 Pagina 30
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