The processes of the biological mass formation and consumption of nutrient elements by the flax oilseed crops under the impact of irrigation and mineral fertilizers have been studied. It was established, that the maximum dry mass formation, the highest accumulation of nitrogen and potassium by the crops occurred on the seventieth day and phosphorus on the eightieth day after appearance of the mass shoots. Strengthening of the mineral nutrition background increased the biological mass of crops and accumulation of nutrient ele- ments in them. The maximum daily uptake of the nutritive elements was between the thirtieth and sixtieth days after appearance of the crop shoots. The increase of the biological mass is the determining factor in the uptake of biogenic elements by plants, which is accompanied by the "dilution effect" of their content in plant organs.