Einfluss von Düngung und Sorte auf Ertrags- und Qualitätsparameter von Verarbeitungskartoffeln im Ökologischen Landbau Effect of fertilization and cultivar on yield and quality factors of potatoes for processing in organic farming

The effect of different sources of K and N on graded yields, dry matter, reducing sugars and quality of french fries and crisps, respectively were examined in two maincrop varieties (AGRIA and MARLEN). Fertilizers applied were cattle manure, potassium sulphate (PS), PS + grinded horn, grinded horn (GH) and a control. Results of two-factorial field experiments (2002-2004) on a loamy sand are presented. Cultivar and fertilizer had a significant effect on final yield, combined mineral K and organic N (PSGH) being the most efficient fertilizer with regard to graded yields for crisp (>40 mm) and french fries production (>50 mm). K content of tubers could be increased, but dry matter was lowered by most fertilizers, so that only the unfertilized plots yielded tubers with a dry matter content favourable for crisp production. As a result of the warm and dry weather in 2003, however, dry matter was high enough, but not too high for french fries (AGRIA), no matter if fertilizer was applied, while in 2004 PSGH lead to a decline in dry matter of around 2.5 %. Further quality parameters important for processing (reducing sugars, crude mash discoloration, after-cooking darkening) were not impaired by fertilization, but variety and storage (4 months at 8°C) had a significant effect