Determination of limiting values of optimum copper supply of oat and barley plants.
In order to determine the copper content required by oat and barley plants (limiting values), pot experiments with increased copper supply as well as plants of high yielding fields were analyzed. Because of the great influence of the nitrogen supply on the Cu‐requirement, the limiting values for Cu should always be related to the range of optimum N‐contents (30–40%o N at the beginning of tillering and 12–20%o at the appearance of the panicle).
From the pot experiments the following limiting values in the dry matter of the aerial parts of oats can bei deduced: 5 ppm Cu at the beginning of tillering and 3 ppm at the appearance of the panicle. For (spring sown) barley the corresponding values are 5.5 and 3.5 ppm Cu.
The limiting values obtained from the field samples are 4 ppm for oats and 5 ppm für barley (both valid for a yield level of 5 t/ha).
In view of their higher yield level, the data of the pot experiments are considered the ‘theoretical’ limiting values.
Determination of toxicity limiting values of Zn, Cu and Pb for oat and red clover.
Toxicity limiting values of Zn, Cu and Pb are determined in order to investigate the causes of growth damages in certain fields. Since the ‘true’ toxicity limit is difficult to estimate, a (somewhat higher) content is called toxicity limiting value resulting after substraction of a significant yield difference.
The pot experiments with increasing fertilization of Zn, Cu and Pb in soil culture gave the following results (summarized in tables in the discussion):.
For Zn the toxicity limit is 410 ppm in oats at the beginning of tillering. In red clover of six weeks age it is only 290 ppm Zn and therefore much lower.
For Cu the toxicity limit is 20 ppm in oats at the beginning of tillering and 18 ppm in six weeks old red clover.
For Pb a toxic effect could be observed above 50 ppm, but this does not seem to be the true limit because of disturbing salt effects.
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