Rapidly reducing phytotoxicity of green waste for growing media by incubation with ammonium

Increasing green waste poses a great challenge to the management of urban environment. Using as growing media could be an environmental-friendly and effective way to dispose of green waste, but it is​ limited by the strong phytotoxicity ubiquitous in green waste. This study assessed the phytotoxicity of six typical green wastes from Southwest China. Their organic composition was identified to find the key phytotoxic substance. After a large number of screening, ammonium salt was selected as detoxifying agent. Incubations with different ammonium salts ((NH4)2CO3, NH4HCO3, (NH4)2SO4) and different dosage (0.5%, 1.0%, 2.0% on a weight basis) were applied on the pruning waste composed of various roadside trees, and their effect of removing phytotoxicity was investigated. Results showed the six green wastes generally had strong phytotoxicity, and the phytotoxicity could be well explained by high concentration of organic acids such as malic acid, citric acid. Five days of incubation with ammonium could dramatically reduce concentrations of six representative organic acids and greatly increase germination indexes. This study concludes that incubation with ammonium carbonate at dosage of 1% would be optimal for the pruning waste, as the organic acid concentration was quite low (<0.1 mg ml−1) and the phytotoxicity was absent (GI>100%). This study will be useful for addressing the key barrier to adoption of green waste as growing media.