In order to determine the effect of a phytohormonal biostimulator on the evolution of morphological traits of hybrid alfalfa, a field experiment consisting of 6 m 2 plots cropped with this plant was set up in 2009. Each experimental variant was carried out in a triplicate. The experiment was run for three years (2009)(2010)(2011). The experimental factor was an extract from Ecklonia maxima, sold under the commercial name of Kelpak SL. This product contains 11 mg dm -3 of auxin and 0.03 mg dm -3

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... of cytokines. In the experiment, it was used on all re-growths as a spray in a dose of 2 dm -3 ha -1 of the formula diluted in 350 dm 3 of water. The analyzed factors were the concentrations of macroelements: phosphorus, potassium, calcium, magnesium (in g kg -1 d.m.), and trace elements: manganese, zinc, copper, molybdenum (in mg kg -1 d.m.) in the aerial biomass of alfalfa plants. The ratios of Ca: P and K: (Ca + Mg) were also calculated. The results were analyzed statistically using the analysis of variance and the mean values were compared with the Tukey's test. The application of the seaweed extract led to an increase in phosphorus, potassium, zinc and manganese in alfalfa aerial biomass. The content of magnesium, calcium, copper and molybdenum did not change significantly in response to the analyzed extract. The modifications in the content of macroelements led to a decrease in the calcium to phosphorus ratio and an increase in the potassium-calcium ratio.