| Summary: | The aim of this study was to determine the effects of soil potassium fertilization (150, 250 and 350 kg K<sub>2</sub>O ha<sup>−1</sup>) and irrigation on the tuber quality (content of ά-tocopherol, β-carotene, essential and endogenous amino acids) of three Jerusalem artichoke (<i>Helianthus tuberosus</i> L.) cultivars (Topstar, Violette de Rennes, Waldspindel). Jerusalem artichokes were grown during a field experiment in the Agricultural Experiment Station in Tomaszkowo (53°42′ N, 20°26′ E, north-eastern Poland). The content of ά-tocopherol and β-carotene was determined at 1.60–2.65 and 0.75–1.00 mg kg<sup>−1</sup> DM, respectively, in all Jerusalem artichoke cultivars produced in north-eastern Poland. High rates of potassium fertilizer (250 and 350 kg K ha<sup>−1</sup>) increased the content of ά-tocopherol in tubers by 47% and 66% on average, respectively. The stimulatory effects of high potassium rates on the content of ά-tocopherol (2.5-fold increase) were observed only in response to irrigation. High rates of potassium fertilizer induced a particularly high increase (3.2-fold) in ά-tocopherol concentrations in Jerusalem artichokes cv. Waldspindel. Irrigation increased ά-tocopherol levels (by 40%) and decreased the concentrations of β-carotene (by 25%) and most essential and endogenous amino acids (isoleucine, leucine, lysine, phenylalanine, valine, alanine, glycine, histidine, serine, threonine). The Topstar cultivar accumulated the highest quantities of essential and endogenous amino acids. Leucine, methionine + cysteine were the limiting amino acids in Jerusalem artichoke tubers. The analyzed tubers were characterized by very high nutritional quality of dietary protein (Essential Amino-Acid Index, 66–78).
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