SUSTAINABLE AGRICULTURE AND PRODUCT QUALITY - A CASE-STUDY FOR SELECTED CROPS

''Sustainable agriculture'' has been defined as a farming system with a low external input of agrochemicals, particularly fertilizer nitroge n. The impact of such farming systems on the quality of three arable c rops was considered. Rape seed, wheat, and potato were selected, becau se 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 environmen tal conditions and cultural practices such as low nitrogen supplies. W ithin three decades, conventional breeding has changed rape seed into a new crop providing oil for human consumption instead for technical p urposes. Wheat (= more complex quality criteria): Wheat is an excellen t source of highly digestible energy for human consumption, but its mo st important quality criterion is the content of protein, which is pos itively correlated with baking quality and with contents of essential amino acids such as lysine and methionine. Since nitrogen is a constit uent of protein, farming systems with little or no fertilizer nitrogen necessarily produce wheat less suited for bread making and of lower n utritional value. At low nitrogen supply, high-protein wheat can be pr oduced only if the grain yield is kept low. Nitrogen fertilization has only a small impact on the contents of vitamins and minerals. Reducti ons in phosphorus fertilization decrease the grain phosphorus content but may increase grain zinc content. Potato (= complex quality criteri a): As compared to wheat, quality traits of potato are less affected b y cultural practices. High potassium levels are essential for tubers o f high quality. In contrast, high nitrogen inputs can have adverse eff ects on several quality traits. The use of pesticides and growth regul ators most often has no direct effects on the quality of seeds and tub ers. 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.