Nutritional status of the seed crop during its vegetative growth is a tool for a reliable yield prognosis. This approach has been validated for oilseed rape in three seasons. The field experimental design was: untreated control, NP, NPK, NPKMgS1 (1/3 total MgS rate, spring applied), NPKMgS2 (total rate, autumn), NPKMgS3 (2/3 -autumn, 1/3 -spring). The concentrations of N, P, K, Ca, Mg, Mn, Zn, and Cu were measured in two stages: rosette (whole plant) and flowering (leaves). The yield prognosis

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... as based on path analysis and stepwise regression. The elevated concentration of P, Ca, and Zn in plants at the rosette stage was the early symptom of nutrient imbalance. The Mg concentration in plant leaves at flowering was revealed as the decisive yield predictor. The manner of its management in plant canopy during the yield forming period (YFP) was crucial for the harvested yield. It was documented that each factor leading to increase in Ca but decrease in Mg concentration resulted in yield decrease. The key reason of Mg shortage was its low uptake during the YFP and simultaneous increase in Mn concentration.