Tall wheat grass (Thinopyrum ponticum) and puccinellia (Puccinellia ciliata) may not be the answer for all saline sites: a case study from the Central Western Slopes of New South Wales

摘要

Emergence and survival of Thinopyrum ponticum cv. Dundas, Puccinellia ciliata cv. Meneman, and Trifolium fragiferum cv. Palestine were observed over three seasons (2004–06) on part of a salinised area in Central Western New South Wales. Grid sampling of topsoils in August 2003 indicated that the site was acidic (mean pHwater 6.05), sodic (exchangeable sodium percentage 29), and saline (estimated ECe 18 dS/m). The site comprised a mosaic of low-salinity (ECe ~6 dS/m) vegetated patches and high-salinity (ECe ~30 dS/m) bare patches where EC was highly variable seasonally (exceeding 100 dS/m) and spatially. Despite suboptimal rainfall, emergence of the grasses was satisfactory on bare patches in all seasons but T. fragiferum failed to emerge in 2004 and was omitted from subsequent sowings. Various methods of ‘engineering’ the bare patches, viz. ditching, mounding, straw mulching, liming, or hand weeding, failed to promote optimum growth of the grasses, although survival was generally enhanced in treatments that included a shallow ditch. Results of the experiments, and observations elsewhere on the salinised area (where some patches supported optimal performance of the three species), suggested that high salinity was the main reason for poor performance on the bare patches. It was concluded that comprehensive site definition, both spatial and temporal, is important before attempting revegetation. Nevertheless the response of T. ponticum and P. ciliata in ditches will be limited on high-salinity sites. In addition, it was observed that surface disturbance and reduced grazing promoted establishment and growth of pre-existing species, particularly Cynodon dactylon and Lolium rigidum. There are many salinised sites in the Central West of NSW where neither P. ciliata nor T. ponticum has performed well, nor would be expected to do so, and where management of native and naturalised species already present may provide the best option for enhancing ground cover and herbage production.