An investigation of water-soluble constituents in anaerobic digestates and growth substrates

Canada is in a waste crisis. A viable alternative to landfill disposal is biological transformation of the organic fraction of municipal solid waste into a product for use as a component in container growth substrates. An anaerobic municipal solid waste digestate, aerobic composts, and a commercial growing substrate, were assessed for potential phytotoxicity using a seed germination bioassay. Compared to a commercial nursery mix, undiluted extracts of the ‘peat-like’ anaerobic digestate were significantly more phytotoxic than the control. Although high soluble salts in the extracts appeared to represent the major contributor to phytotoxicity in aerobic composts, there was less correlation in this regard for the anaerobic digestates.; Soluble salts are common phytotoxins. Although easily measured, the results obtained using different methods have been difficult to interpret. Two experiments were designed to (1) compare soluble salts extracted using different methods, and (2) to examine the response of nursery crops to different methods of fertilisation and relationship to substrate electrical conductivity.