During the course of the DOC trial in Therwil (BL), the effects of organic and conventional farming systems on the yield of crops and clover grass have been investigated on a fertile loess soil for 28 years. The farming systems differed in particular with regard to fertilisation and plant protection. The organic systems achieved a mean yield of 80 % of the yield by conventional farming methods over the course of 28 years and with all crops, and this was achieved with a lower application of mineral nitrogen of only 30 to 35 %. Yield losses when using the organic systems for farming crops since the start of the trial were at 33 to 43 % greatest among potatoes and at 13 % smallest with clover grass. Yield losses of winter wheat were 14 %. The potato yield of the bio-organic farming system was on average 10 % higher than with the bio-dynamic system and the yield of clover grass conventionally grown with manure was 10 % higher than yield of clover grass grown with mineral fertiliser. The yield stability of the organic systems tended to be lower. Potatoes showed greatest yield fluctuations.Yield comparisons under farming conditions in Switzerland showed that yield of organically grown wheat in the DOC trial was similar, whereas yield of conventionally produced wheat was lower due to using varieties with weak yield production. In the case of potatoes, the DOC yield was higher under organic and conventional farming conditions in comparison with Swiss farms.