Impact of agronomic measures on yield and quality of organic potatoes (Solanum tuberosum L.) for industrial processing

Three field experiments were conducted during 2002 and 2004 on two sites in Germany in order to examine the impact of preceding crop, pre-sprouting, N- and K-fertilization and cultivar on total tuber fresh yields, tuber DM, glucose and fructose concentration, as well as the colour of crisps and the quality score of French fries at harvest and after storage. Generally, total tuber yields depended very much on the growing season. However, highest yields were obtained when horn grits were applied along with potassium sulphate. Increasing yields after cattle manure fertilization could be attributed to K rather than N. Combined N and K fertilization may cause DM concentration to fall short of the required minimum for crisps. Pre-sprouting and storage increased tuber DM concentration considerably. Cultivars belonging to the very early and early maturity type showed the largest relative increase of reducing sugars due to storage. On the whole, results suggest that the effect of agronomic measures such as fertilization, preceding crop and seed-tuber preparation may be rather small and the response of internal tuber quality and quality of fried products difficult to predict. The quality standards for tuber raw stock can be accomplished best when adequate cultivars suitable for storage are chosen.