The Influence of varying Amounts of Nitrogen, Copper and Magnesium on the Yield of Oat1. In pot experiments with oat high amounts of copper (500 mg) copper sulfate/pot, comparable to 50 kg (Cu/ha) together with a high nitrogen supply as calcium nitrate led to a remarkable increase in yield of grain in comparison to a normal copper fertilization (50 mg copper sulfate/pot, comparable to 5 kg Cu/ha). When using high amounts of ammonium sulfate the observed effect of high amounts of copper was only small.2. According to the results and to the copper content and copper uptake of the plant it was concluded, that nitrogen fertilization given as ammonium sulfate increased the availability of soil copper and/or fertilizer copper presumably by affecting the soil reaction. Nitrogen fertilization given as calcium nitrate therefore needs a higher copper level in the root medium either from soil or fertilizers in order to obtain the maximum yield.3. It was assumed that the form of nitrogen fertilizers was responsible for the different availability of copper in these experiments, as the amount of available copper in the soil increased with the lowering of soil pH due to ammonium sulfate addition.4. The high copper supply to the soil remarkably reduced the harmful effect of high amounts of nitrogen given as calcium nitrate but not as ammonium sulfate.5. The nitrogen fertilization with calcium nitrate, especially in combination with a high copper supply, resulted in the reducing effect of a magnesium deficiency.6. The harmful effect of high amounts of nitrogen, especially in the ammonium sulfate form, upon yield was reduced by an optimal magnesium supply.7. The results presented suggest that for evaluating the copper status of the soil and for estimating the demands of copper fertilization, soil reaction and its change by the form of nitrogen fertilizers should more be taken in consideration.
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