Organic potato cultivation in Western Europe is predominantly nitrogen-limited and defoliation of the crop canopy caused by late blight may further reduce tuber yield. The aim was to find cultivars that are both, able (a) to use the available N as efficiently as possible and (b) be relatively tolerant to late blight. Another objective of the study was to examine a range of methods available to (c) assess crop N status and (d) describe characteristics of canopy architecture. Results from the first year (2009) indicate that even at the same N supply cultivars from a range of maturity groups can be differentiated in terms of their genotype-specific chlorophyll and leaf N concentration. Data also show that the risk of nitrate losses after harvest due to leaching may be aggravated by the fact that some cultivars take up marked amounts of N, but translocate relatively little into the tuber. Overall, first year results on crop N status and tuber growth duration indicate that an earlier harvest of tubers than common practice, may be suggested, to allow subsequent crops to catch the residual mineral N
