Excess ammonium causes toxicity in watermelon and cucumber plants grown in nutrient solution

Excess nitrogen (N) in the form of ammonium (NH 4 + ) in the culture medium can induce ammonium toxicity, causing physiological disturbances in plants and resulting in impaired growth and dry matter production. Thus, the aim of this study is to evaluate the growth and dry matter production of watermelon and cucumber plants grown under different nitrogen concentrations in the ammoniacal form and in nutrient solution. The experiment was carried out at the Department of Plant Science located at the Center for Agricultural Sciences, Federal University of Piaui, during the period from October to November 2017. Two cucurbit species, watermelon and cucumber, were studied separately for each experiment using a completely randomized design, with four replicates and five treatments, corresponding to the following ammonium concentrations: 0.5; 2.2; 4.5; 8.7; and 14.0 mmol L -1 NH 4 + . Twenty-one days after transplanting the watermelon and cucumber seedlings, the following variables were analyzed: leaf area, leaf chlorophyll index, plant height, stem diameter, root volume, root length, root dry matter, and shoot dry matter. Excess ammonium in the nutrient solution causes toxicity in watermelon and cucumber plants, decreasing plant growth and dry matter production. Symptoms of ammonium toxicity are more evident in the cucumber plant, which presented chlorosis and necrosis followed by plant death after 15 days of cultivation.