Abstract
Mineral nutrient requirements for maximum growth rate of cucumber (Cucumis sativus L.) seedlings are estimated on the basis of three criteria. 1. The optimal weight proportions among the nutrients present in the seedlings. In relation to N = 100, close to 75 K, 13 P, 9 Ca, and 9 Mg are required. 2. The optimal ratio between the nitrogen sources NH(4) and NO(3) in the solution. The best growth is recorded with about equivalent amounts. Nitrate alone is also highly productive. Cucumber prefers nitrate and is sensitive to high ammonium concentrations. 3. The optimal total concentration in the solution corresponds to 200 to 300 milligrams of nitrogen per liter, with the proportions of the nutrients according to criterion 1. Simple growth methods are suggested in which the three criteria are fulfilled.Calcium, especially, is found to accumulate in older leaves. It is proposed that this is not an expression for a physiological requirement for calcium but a mechanism for deposition of excess uptake important in adaptation to calcareous soils. This mechanism also operates at low calcium uptake rates, causing deficiency in the young parts, despite relatively high contents in the old leaves. Cucumber is therefore interpreted to be an obligate calcicole. The results are discussed in relation to similar experiments with birch (Betula verrucosa Ehrh.) seedlings, a species able to grow on very acid soils.