Rapid root development in clay subsoils enhances the early growth of native grassland species

Wildflower meadows are a low-maintenance landscape treatment that can improve urban biodiversity and achieve conservation outcomes, especially when designed to use plants from threatened grassy ecosystems. Cost-effective approaches to create meadows include direct seeding onto mined sand substrates that are placed onto site soils to supress weed competition and enhance sown plant establishment. However, waste subsoils diverted from landfill could provide a more sustainable alternative. This study compares a mined sand with a clay subsoil to understand the relative differences in sown plant establishment and root growth for a range of south-east Australian grassland species.

Germination, seedling emergence and root development were assessed for six species sown in an 80 mm deep cap of two low nutrient substrates (sand and clay subsoil) overlying a simulated site soil. Rhizoboxes were used to assess the rate at which plant roots could access soils beneath capping substrates.

Sand and clay subsoil supported the establishment of the six sown species. Five species had significantly greater total root length, leaf area and aboveground biomass when sown in recycled subsoil, compared with sand.

Edaphic conditions affect the establishment of native grassland species in wildflower meadows. Compared to sand, recycled clay subsoils provide a more sustainable alternative for establishing designed wildflower meadows and can support rapid root and plant growth in south-east Australian grassland species.