 High concentrations of mineral salts in solution within the growing medium can have phytotoxic effects.Sources of excessive mineral salts include infiltration of seawater and excessive application of fertilizers.For example, urea is used in agriculture as a nitrogenous fertilizer, but if too much is applied, phytotoxic effects can result, either by urea toxicity or by the "ammonia produced through hydrolysis of urea by soil urease".