The requirements of cabbage and lettuce seedlings for potassium in the presence and absence of sodium

Abstract

Sand culture experiments were performed in the glasshouse to determine the internal potassium concentrations required by lettuce and cabbage seedlings. Because the presence of sodium in the nutrient medium may have affected the potassium requirements, the experiments were repeated with and without sodium in the medium. The critical concentrations of potassium for maximum plant size varied as the plants grew larger because the potassium concentrations tended to increase over time. However, critical concentrations for maximum relative growth rate (RGR) were almost independent of time or plant weight. In the absence of sodium, the critical levels for a 10% reduction in RGR of cabbage was 2.2%K in the dry matter and for lettuce was 4.3%. In the presence of sodium, the corresponding critical levels were 0% and 1.0%, demonstrating that cabbage was more able to substitute sodium for potassium than was lettuce. Levels of sodium in commercial fields in the U.K. tend to be fairly low, suggesting that the critical levels determined in the absence of sodium would usually be more applicable.

Key words:

• Brassica oleracea var. Capitata
• Critical concentration
• Lactuca sativa L.