Evaluation of physicochemical characteristics of invasive Acacia waste cocomposted with pine bark for horticultural use.
The rising cost of peat moss boosted the demand for alternative organic materials for container growing media. In this study, residues from the control of invasive Acacia longifolia cocomposted with pine bark were evaluated as alternative constituents for horticultural substrates. The composts showed high-quality physical characteristics to replace peat moss in substrate formulation, namely, particle size, total porosity, air capacity, total water-holding capacity and volume shrinkage within the established limits for an ideal substrate. Compost bulk density was below 0.4 g cm-3 and total pore space above 85% of the total volume, as recommended for substrates. Compost chemical characteristics such as pH and electrical conductivity were appropriate for substrate constituents compared to other domestic, industrial and livestock waste composts that have been recommended for mixing with peat for substrate composition. Compost cation exchange capacity and C/N ratio values were suitable for substrate composition and the NH4+-N to NO3--N ratio in composted products suggested a stable or mature material. The contents of macronutrients, except for calcium, were generally below those found for commercial substrates but these are usually additionally fertilized with mineral fertilizers. Residues from Acacia shrubs with pine bark provided a feedstock material with sufficient biodegradability and structure for effective composting and produced composts with expanded end-use to horticultural nursery applications, compared with urban, industrial or livestock waste composts. Composts were suitable for compost use for soil improvement and also as a substrate constituent in high-value horticultural applications.