To be able to meet future quality demands and demands for lower cadmium content in food we wanted to investigate the possibility to influence the cadmium content in potato by changing the management factors. Field trials with two potato varieties, one high accumulating and one low accumulating, showed that at a low nitrogen level, 60 kg N/ha, the cadmium content in tubers increased compared to higher applications like 160 and 240 kg N/ha, respectively. Soil pH is important for the availability of cadmium and at low pH the plant available cadmium concentration increases in most soils. The form of nitrogen supplied influences soil pH and thus the availability of cadmium. Field trials including NPK 11-5-18 micro, calcium nitrate and ammonium sulphate showed that potatoes fertilized with ammonium sulphate contained higher amounts of cadmium than those fertilized with NPK. When plants take up ammonium ions they balance the charges by excluding hydrogen ions, resulting in a lowering of the pH in the surrounding soil. Interestingly, fertilization with calcium nitrate also resulted in a higher cadmium concentration compared to NPK. Possibly, the included calcium ion may have contributed to higher cadmium availability by switching places with cadmium ions on the soil particles. According to this study, it is best to fertilize with a balanced and pH neutral nitrogen fertilizer to be able to limit the cadmium content in potato tubers.
The project was financed by the Swedish Farmers’ Foundation for Agricultural Research and The Partnership Alnarp in 2006-2009.
Project members are Helene Larsson Jönsson, Helene.Larsson.Jonsson@slu.se , Håkan Asp & Charlotte Gisse´n