THE EFFECT OF NITROGEN AND POTASSIUM LEVELS IN TUNG SEEDLINGS ON GROWTH, APPARENT PHOTOSYNTHESIS, AND CARBOHYDRATE COMPOSITION

Nitrogen and potassium are the two fertilizer elements that are needed in largest amounts in most tung orchards of the southern United States. Supplying these elements at the optimum rates and in the proper ratios is an important nutritional problem. Leaf analysis has proved to be a valuable criterion of the nutritional status of tung trees, and, as more basic information on the relation of mineral composition to physiological processes and biochemical constituents is accumulated, it should become even more useful. For example, it would be helpful to know the effect of certain concentrations and ratios of nitrogen and potassium in the leaves on the rate of photosynthesis, which in turn must be intimately related to growth, productivity, and storage and utilization of carbohydrates. The sand-culture technique seemed the best approach to this problem since it afforded a high degree of precision per number of plants, together with greatest ease of control and manipulation. The usual procedure in water or sand cultures is to grow plants in solutions in which the nutrient salts are maintained at definite levels and ratios, and subsequently to make chemical and physiological tests on the plants and on residual or effluent nutrient solutions. In the present study an attempt was made to develop rather specific differences in levels of minerals in the leaves. The composition of representative plants was determined from time to time and the nutrient solutions were adjusted as necessary to produce as nearly as possible the desired mineral concentrations in the plant tissue. The objectives of this experiment were (1) to grow plants containing three levels of nitrogen and potassium in factorial combinations, while maintaining other elements at optimum or above deficiency concentrations, and (2) to determine the effect of these nutritional variations in the plant on growth, apparent photosynthesis, and chemical composition.