The potential of aged Acacia melanoxylon bark as a source for alternative substrate.
Acacia melanoxylon (AM) is a fast-growing tree, native to Australia. It has good adaptation to degraded soils resulting from habitat disturbances (wildfires) making it a highly invasive plant. Alien tree control actions involving debarking processes may potentiate Acacia bark residues valorization for substrates formulation. This work aims to study the viability of AM bark use in substrate mixtures. The first experiment was the assessment of bark particle size (4 and 10 mm hammer mill sieve size) and aging effect on bark phytotoxicity (cress seed test). Independent from granulometry, fresh bark (FB) was phytotoxic for cress seeds, presenting Munoo-Lisa vitality index (MLVI) lower than 20%. After 8 weeks phytotoxicity was removed, and aged barks (AB) showed seed performance (MLVI of 95.3 and 103.1%) equal to peat-only control substrate (100%). A second experiment compared FB and 8 weeks aged bark (AB) of two particle sizes (4 and 10 mm) as a substrate component. Barks were mixed 25 and 50% (v v-1) (M25; M50) with peat and tested in a pot experiment with Chinese cabbage. 50% FB substrates revealed Chinese cabbage growth inhibition. On the contrary, all AB mixtures recorded plant growth statistically equal to peat-only control substrate, suggesting the feasibility of using aged bark up to 50% in future substrate preparations.