Methods of quantitative diagnosis of the nutritional status of the young plant and quantitative prognosis of final yield were based on preliminary models constructed by using selected results ('pure'-effect data) from pot experiments with oats and spring wheat. The bases of the models -a fixed dry matter weight level of aerial parts of the plant and absolute and relative reference values -and the procedure by using the models were tested by relationships between predicted and obtained final yields. Highly significant correlation coefficients > 0.9 (p < 0.001) were found.

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Methods of diagnosis, yield prognosis and therapy, main part of a fertilization system for spring sown cereals, based on results from pot experiments were successfully transferred to results from field experiments in Scandinavia under widely varying conditions. At the selected DMw-level of 0.2 g per plant the optimal chemical composition of the young plant associated with highest obtained yields was: 5.0%N, 0.55%P, 5.2%K, 0.10%Na, 5.3% (K + 89 0.15% Mg, 1.0% Ca, 60 ppm Mn and 8 ppm Cu.The optimal chemical composition was independent of species and variety, soil type and region, allowing the methods to be based on solely one set of models.The selected DMw-level -model niveau or standard dry weight -was low compared with that for pot cultures making early diagnosis and therapy possible under field conditions.A correction model was developed in order to estimate the chemical composition of the plant at model niveau from the chemical composition of the plant sampled at any time during early growth and with the view to apply the fertilization system to agricultural practice.

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