EFFECT OF INCREASING NITROGEN-FERTILIZATI ON ON COPPER DEMAND IN CEREALS

Pot experiments were conducted with wheat (2 experiments) and spring b arley (1 experiment) in a peat soil. Four N and four Cu fertilizer lev els were chosen in such a way that, based on grain yield, within each N level there was a Cu deficient and a Cu sufficient treatment. For su fficient Cu supply, Cu level in soil and plant increased with increasi ng N level. Critical Cu concentrations in aboveground biomass at shoot ing [mu g (g dw)(-1)] were 3.5 (lowest N level = N-1) to 7.5 (highest N level = N-4) for grain production of wheat and barley, but for above ground biomass of wheat at shooting they were only 2.6 (N-1) to 5.8 (N -4). Based on critical Cu concentration at different N levels, critica l Cu/N ratios were determined. These were independent from N level, in dicating that Cu remobilization in the older leaves is unlikely even a t N deficiency. The high critical Cu concentrations at high N levels m ay be explained by an increased immobilization of Cu. Under Cu deficie nt conditions, Cu concentration did not increase with increasing N lev el. However, under Cu sufficient conditions, N concentration and Cu co ncentration of the plant increased with increasing N level. The increa sing Cu uptake with increasing N level may be explained by the release of amines into the root apoplast and the rhizosphere. Particularly un der Cu sufficient conditions, these may mobilize Cu by formation of so luble Cu-amine complexes.