“Sustainable agriculture” has been defined as a farming system with a low external input of agrochemicals, particularly fertilizer nitrogen. The impact of such farming systems on the quality of three arable crops was considered. Rape seed, wheat, and potato were selected, because they represent arable crops with simple to complex quality criteria.Rape seed(= simple quality criteria): The oil quality is determined primarily by the genotype and is only slightly affected by environmental conditions and cultural practices such as low nitrogen supplies. Within three decades, conventional breeding has changed rape seed into a new crop providing oil for human consumption instead for technical purposes.Wheat(= more complex quality criteria): Wheat is an excellent source of highly digestible energy for human consumption, but its most important quality criterion is the content of protein, which is positively correlated with baking quality and with contents of essential amino acids such as lysine and methionine. Since nitrogen is a constituent of protein, farming systems with little or no fertilizer nitrogen necessarily produce wheat less suited for bread making and of lower nutritional value. At low nitrogen supply, high‐protein wheat can be produced only if the grain yield is kept low. Nitrogen fertilization has only a small impact on the contents of vitamins and minerals. Reductions in phosphorus fertilization decrease the grain phosphorus content but may increase grain zinc content.Potato(= complex quality criteria): As compared to wheat, quality traits of potato are less affected by cultural practices. High potassium levels are essential for tubers of high quality. In contrast, high nitrogen inputs can have adverse effects on several quality traits. The use of pesticides and growth regulators most often has no direct effects on the quality of seeds and tubers. Generally, customers should be willing to pay more for food which is of a high ecological quality but may be inferior in technological and nutritional quality.