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The 'IOSDV field experiment, testing mineral-nitrogen fertilizer in combination with different forms of organic manure over a period of 6 years (two crop-rotation cycles) has provided specific results concerning the interaction of the components of fertilizers. Stable manure had an intensive effect on sugar beet but only a weak effect on winter wheat. Sugar-beet leaves had a strong effect on winter wheat but little effect on winter barley. Straw-green manure showed a growing effect on winter barley. As expected, the effect of fertilizing is influenced by climatic factors. Yield curves with the specific parameters 'M', 'm' and 'i' show -- as would be expected -- that the effect of the organic manure on yield is chiefly expressed at lower levels of mineral-nitrogen manure. In this way, the curves indicate the optima] level of N-fertilization. The balance of nutrients show that organic variances have different effects on the N-balance. The interval evaluation shows the importance of long-term experiments. [ABSTRACT FROM AUTHOR]