Developing extruded seed pellets to overcome soil hydrophobicity and seedling emergence barriers.
Globally, soil water repellency is a major constraint to plant establishment, restricting water infiltration and moisture retention in the seed zone which results in poor germination and seedling emergence. To address this problem within an ecosystem restoration context, we investigated the use of a surfactant in extruded seed pellets to improve native plant recruitment in water-repellent topsoils of two proteaceous woodland species, Banksia menziesii R.Br (glasshouse trial) and Lambertia inermis R.Br (field trial). In this two-part study, we first examined B. menziesii seedling performance in detail under glasshouse conditions for differences in survival between the extruded pelleting formulations after an induced drought at 12 weeks. We demonstrated that there was no difference in seedling emergence amongst control seed and pellet treatments in B. menziesii. Initially, B. menziesii seedlings emerged faster in the control treatment (non-pelleted control seeds) and had greater initial plant growth (leaf and root production), however by Week 12, seedlings generated from pellets were not significantly different from the control seeds and pellets + surfactant had the greatest number of leaf establishment. Survival after drought of B. menziesii seedlings ranged from 14 to 31 days with pellet + surfactant surviving approximately 2.6 days (11.8%) longer than the control seeds. For the second species, L. inermis, seedling emergence under field conditions was approximately 24% greater in seedlings derived from extruded pellets; however, there was no difference in overall survival due to post-emergence predation. This study provides a proof of concept that seedling emergence in water-repellent soils can be enhanced with extruded pellets containing surfactants. Our demonstration under in situ and ex situ conditions confirms the prospective use of seed enhancement technologies with future development and field-testing warranted.