PLANT GROWTH AND TOMATO YIELD AT SEVERAL NITRATE/AMMONIUM RATIOS AND BICARBONATE CONCENTRATIONS

Abstract

The main effect of different nitrate/ammonium ratios and bicarbonate concentrations in the nutrient solution on growth of plants has been reported, but little is known of the influence of the interaction of these two factors on tomato (Lycopersicon esculentum Mill.). Therefore, two studies were conducted to determine the influence of three nitrate/ammonium percentage ratios (100/0, 85/15 and 70/30) and three concentrations of HCO₃-(0, 2.5, and 5 mol_c m^-3) in the nutrient solution on growth, yield and mineral composition of tomato ‘cv. Slolly F-1’ grown in hydroponics. The 70/30 nitrate/ammonium ratio reduced (P ≤ 0.05) dry weight and the root volume, while the concentration of 5 mol_c HCO₃- m^-3 decreased diameter of stem, leaf dry weight, root volume and stem/root ratio of young plants. The calcium concentration in leaves and stems of young plants and mature plants decreased (P ≤ 0 .05) with the 70/30 ratio. In contrast, the phosphorus concentration in such organs increased (P ≤ 0 .05). The addition of 5 molc HCO₃- m^-3 to the nutrient solution reduced (P ≤ 0 .05) the phosphorus concentration in leaves and stems of young plants, and stems and fruits of mature plants. The 70/30 and 0 molc HCO₃- m^-3 interaction caused an increment (P ≤ 0.05) in height of young plants and reduced magnesium concentration in leaves and stems. When 30 % of nitric nitrogen was replaced by ammonium nitrogen or 5 molc HCO₃- m^-3 were added to the nutrient solution in the stage of young plant, some indicators of growth diminished but fruit yield was unaffected.