Sensitivity of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) to excessive copper foliar spray concentration when grown in a calcareous soil

Copper (Cu) foliar spray is a requested technique to prevent Cu deficiency in cereals grown in calcareous soil. The reasonable Cu foliar feeding requires identifying the Cu phytotoxic threshold. Such a threshold will help producers to prevent the negative impact of excessive foliar Cu application. The aim was to compare the phytotoxic effect of foliar Cu spray on wheat and barley. The field experiments were conducted in calcareous soil (16.5% of free carbonates) that contains 0.26 mg kg(-1) of Cu (DTPA-Extraction). Six Cu foliar spray concentrations were tested in wheat (0% or control; 0.2%; 0.4%; 0.6%; 0.8% and 1%) and barley (control; 0.2%; 0.4%; 0.6%; 1% and 2%) using a randomized complete blocks with five replications. Leaf Cu was supplied at the stem extension and booting stages using the sulfate form (CuSO4.5H(2)O). Cu foliar spray of 0.2% resulted in leaf damage for wheat. Barley did not show phytotoxic symptoms even at 2% of Cu. A significant decline in wheat grain yield (-20%) was recorded at Cu foliar spray of 1% compared to control. For barley, a grain yield decline (-14%) was induced at 2% Cu foliar spray compared to the optimum yielding recorded at 0.94% of Cu. The Cu flag leaf content reached 130 and 13 mg.kg(-1), respectively, for wheat and barley at 1% of sprayed Cu. The flag leaf contents on other nutrients were invariable. The current study demonstrates that the negative impact of Cu phytotoxicity was more pronounced in wheat compared to barley at excessive Cu concentration of foliar feeding.