Vegetables have a significant place in the healthy eating pyramid. It is recommended that vegetables should be consumed as often as possible to provide nutritional and biologically active substances. The aim of the present study was to determine the biological value of the leaves of rocket as affected by different regimes of plant nitrogen and potassium nutrition. Plants were grown in a peat-based medium under greenhouse conditions. After harvest, the contents of L-ascorbic acid, chlorophyll, flavonoids, glucosinolates and essential oil were determined in the rocket leaves. The average content of chlorophyll a + b per 100 g of rocket fresh biomass was 1.16 mg, while the L-ascorbic acid concentration – 92.66 mg. 100 g of dried rocket leaves contained on average 0.84 g of flavonoids and 0.15 ml of essential oil, while 1 g of dry plant material was characterized by the presence of 10.56 μmol of glucosinolates, on average. Potassium chloride proved to be an interesting source of potassium; its application significantly increased the concentration of glucosinolates in the rocket leaves. However, this form of potassium was not found to have a significant effect on the accumulation of L-ascorbic acid, chlorophyll, flavonoids, and essential oil. An increased rate of nitrogen contributed to a decrease in the content of L-ascorbic acid and glucosinolates. The presented results show that it is possible to modify the chemical composition of rocket leaves by using an appropriate system of plant mineral nutrition.

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