Composting acacia biomass with pine bark

Abstract

Acacias are invasive Fabaceae species that can be composted to produce organic amendments and horticultural substrates. With this aim, big piles were set up with ground and screened acacia residues and pine bark, and managed with different turning frequency, to analyze the physicochemical characteristics during composting and to model the breakdown of acacia organic matter (OM). Temperatures were >60^oC for several months, indicating pathogen inactivation, seed destruction and high amount of biodegradable OM (600-620 g kg^-1 of initial OM). High temperature and high pH conditions promoted significant N losses (450-470 g kg^-1 of initial N). Nevertheless, these were smaller compared to C losses and so the C/N ratio decreased from 56 at the beginning to 40-41 at the end of composting. This study indicates that composting acacia can produce organic amendments with high OM content, and low electrical conductivity (<0.7 dS m^-1). However, a long period of composting is required to achieve advanced compost maturation.