Evaluating Microdictyon umbilicatum bloom biomass as a compost conditioner for Australian, native coastal plants, Rhagodia candoleana and Banksia integrifolia
There is little or no published information on the use of Microdictyon umbilicatum as a compost component or soil conditioner for plants; yet it is one of the increasing numbers of blooming green tide macroalgae that requires solutions for the management of biomass. This project was established to determine both the suitability of the macroalgal bloom biomass for composting, and if application on local native plant species used in coastal revegetation programs was safe and/or beneficial. M. umbilicatum macroalgal biomass was collected from Currambene Creek (Jervis Bay) in March 2011 and three different proportions (5, 10, and 20%) were added into a greenwaste mix for composting, alongside a control compost without macroalgae. The proximate composition and soil conditioning quality of the resulting compost treatments was tested. Two Australian native plant species, Saltbush (Rhagodia candoleana) and Coastal Banksia (Banksia integrifolia), were grown in these treatments in a 1:1 ratio with potting mix for 14 weeks. Plants in the 5% treatment exhibited increased growth rates of 157% (F = 8.9, p = 0.001) for R. candoleana and 73% (F = 4.7, p = 0.015) for B. integrifolia. Leaf numbers for R. candoleana were also significantly greater (F = 8.26, p = 0.002) in the 5% treatment, compared to all other treatments. For 10 and 20% treatments, growth rates and leaf numbers were equal to the control group. These outcomes confirm that, as an organic additive, M. umbilicatum bloom biomass can provide a safe soil conditioner at Australian Standards with significant benefits for plant growth for two coastal plant species. It also demonstrates an effective and valuable use of a marine resource, otherwise regarded as a nuisance.