Lettuce and cabbage growth and nutrient uptake response to invasive Acacia waste composts

Peat moss and pine bark have been traditionally used in the production of horticultural substrates. However, there is an increasing demand for alternative materials to produce horticultural substrates. In order to determine the potential use of composts made of shredded biomass from the control activities with respect to the invasive Acacia species (Acacia longifolia and Acacia melanoxylon) as an alternative to pine bark compost for the production of horticultural substrates, we assessed the effect of increasing rates of composts of Acacia in a commercial substrate, on growth of lettuce (Lactuca sativa L.) and savoy cabbage (Brassica oleracea sabauda L.). The replacement of pine bark compost by Acacia compost did neither affect lettuce nor cabbage growth negatively, thus suggesting that Acacia compost can be successfully used as an alternative constituent for horticultural substrates. Increased growth and nutrient uptake was found for lettuce and cabbage in treatments with Acacia compost compared with bark compost, which may be explained by the lower C/N ratio and the increased availability of N in the Acacia compost, compared with pine bark compost. Therefore, Acacia composts can be recommended for substrate formulation, although it may be needed to decrease its electrical conductivity and pH value by mixing it with other constituents such as peat. Crop and container characteristics must be considered for recommendations about the optimum proportion of Acacia compost in final substrate composition.