Excess nitrogen in the ammonium form may induce different nutritional disorders in plants depending on the species cultivated. Therefore, the objective herein was to evaluate the accumulation of nutrients, growth and the visual symptoms in rice and spinach plants in function of ammonium concentrations in the nutrient solution. Two experiments were performed with rice and spinach plants in a greenhouse, at the Unesp Campus of Jaboticabal-SP, Brazil. In each experiment five ammonium concentrations were used (10, 20, 40, 80 and 100 mmol L-1), arranged in a randomized block design with five repetitions. The effects of excess ammonia were studied on the green color index, electrolyte leakage, accumulation of N, Mg, K and Ca in the shoots, leaf area, height, dry matter of root, shoots and whole plant, and also characterization of the visual symptoms of toxicity in the plants. These effects of excess ammonium reported above are reflected in the production of plant dry matter, with a linear decrease in dry matter of the roots, shoots and whole plant. Excess ammonia in the nutrient solution decreased accumulation of dry matter due to reduced leaf area and increased cellular electrolyte leakage which induced symptoms characteristic of ammonium toxicity in both species, and also decreased uptake of Ca, Mg and K in rice plants and only Ca in spinach plants.
Key words: Abiotic stress, ammonium nutrition, Oryza sativa, Spinacia oleracea.