Revegetation of a scalded saline discharge zone in Central Queensland. 1, Selection of tree species and evaluation of an establishment technique

Species selection trials using 38 tree species were undertaken on salinised, waterlogged land [watertable within about 1 m of soil surface, electrical conductivity (ECw) about 30 dS/m, surface soil (0-0.1 m) EC1:5 about 10 dS/m] in coastal central Queensland. Casuarina glauca and C. obesa gave best survival and growth, while Eucalyptus camaldulensis and C. cunninghamiana gave good initial survival but succumbed to salt and waterlogging stress after several years. The role of soil mounding and mulching for the establishment of C. glauca was investigated in a factorial experiment involving 2 levels of soil mounding (nil, 0.15 m) and 4 mulch conditions (nil, hay, black plastic, white plastic), and in a second experiment involving bagasse, soil amendment with calcium, and the installation of a double ridge in the mound. The low soil mounding had little effect on plant survival or growth, or soil conductivity; however, mulching greatly influenced these parameters (e.g. about 2 years after a summer planting, tree survival, tree growth, and surface soil conductivity in a plastic mulch treatment was 566, 210, and 60%, respectively, of values of the no-mulch treatment, with a mean tree height of about 3 m in the plastic mulch treatment). Plastic mulch was recommended over hay or bagasse mulch for short-term (<2 years) increase in plant survival and growth (e.g. 15 months after a summer planting, height of plants established in plastic mulch rows was 124% of that in hay-mulched rows). The incorporation of a small trough in the crown of the bed was found to improve plant growth significantly (tree height in troughed mounds 120% of that in untroughed mounds, 15 months after planting), but did not improve establishment. Soil amelioration with lime, gypsum, or dolomite at 3.0 t/ha did not improve plant growth. A further trial at another salinised site confirmed the success of the plastic mulch-crown trough technique, relative to conventional preparation techniques (i.e. ripping).