Toxicity of ammonia to plants

Abstract

The toxicity of ammonia was evaluated and an estimate is given of (mass) concentration for no adverse effect: 75 μg/m³ for a yearly average, 600 μg/m³ for 24 h and 10 000 μg/m³ for 1 h. Ammonia can cause various types of injury, including necrosis, growth reduction, growth stimulation and increased frost sensitivity. Several plant species have been assessed for sensitivity to ammonia. Some conifer species were relatively sensitive to low concentrations in the long term; some cultivars of cauliflower and tomato were relatively sensitive to somewhat higher concentrations for a short term. Plants were more sensitive in the dark than in daylight and better adapted to ammonia in high than in low temperatures. Availability of carbohydrates probably plays an important role: the plant can detoxify ammonia as long as it can convert ammonia into amino acids.

Special attention has been paid to plant injury around intensively managed livestock. The emission from these sources consists of a large number of components, ammonia proving to be the main toxic component.