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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]

An interpretation of LIEBIG's "law of the minimum", LIEBSCHER's and WOLLNY's "law of the optimum" and MITSCHERLICH'S "law of constant activity" for two growth factors is presented. With three-quadrant diagrams (crop yield vs. N fertilization, crop yield vs. N uptake, N uptake vs. N fertilization) a long-term field experiment in Göttingen (Ackerbau-Systemversuch) is analyzed. This experiment started 1981 with the following treatments: 1. crop rotation (a: short rotation, sugar-beet, winter-wheat, winter-barley/vetchgreen- manure; b: long rotation, sugar-beet, winter-wheat, winter-barley, lucerne, maize, faba beans); 2. chemical plant protection (a: with; b: without); 3. mineral nitrogen fertilization procedure (a: N-fixed, cumulative effects; b: N-rotating, one year's effects of different N fertilization); 4. mineral nitrogen fertilization (a: nil; b: suboptimal; c: optimal; d: hyper-optimal doses). Without chemical plant protection resource use efficiency of applied nitrogen decreased according to LlEBSCHER's and WOLLNY'S "law of the optimum". In most cases this "law of the optimum" was applicable to the empirical data. LIEBIG's "law of the minimum" and MITSCHERLICH's "law of constant activity" are exceptional cases, whereas LiEBSCHER's and WOLLNY'S "law of the optimum" has more general validity. For maximal resource use efficiency the growth factors have to be combined in optimal amounts. [ABSTRACT FROM AUTHOR]