Determination of productivity, rooting and nutrient profile of Acacia mearnsii (black wattle) hedge plants

The poor rooting of black wattle, Acacia mearnsii, has previously limited its commercial propagation, but research at the Institute of Commercial Forestry has enabled many commercial nurseries in South Africa to supply the industry with rooted cuttings. This paper provides an understanding of the management of A. mearnsii potted hedge plants with regards to productivity, rooting ability and profiling foliar nutrients. Hedge plants in two bag sizes (5 l and 40 l) of differing ages (8 months and 24 months) were investigated. No significant differences were noted in rooting between bag sizes. However, when coupled with productivity data, the 40 l hedge plants generated higher numbers of predicted rooted cuttings. Although the productivity in both bags increased over time, rooting ability declined, possibly because of observed increases in N and S and decreases in P, Mg, Fe, Zn and B, all of which are important for root growth and development. Productivity results indicate that hedges can be kept for at least 53 months before needing replacement. Rooting results showed no decrease in productivity or rooting from cascaded hedge plants. Results from the nutrient profiling of foliar data provide a unique benchmark for nurseries to successfully manage their hedge plants.