Effects of Burial Depth, Watering Regime and Soil Amendments on the Establishment of Four Arid Zone Species

Direct seeding of restorative plants is a difficult task in arid environments due, in part, to the low moisture levels inherent to these areas. This barrier to restoration has stimulated a number of methods to help combat this issue, including the burial of seeds just below the soil surface, the addition of fertiliser and the use of other suitable low-cost soil amendments aimed at improving germination and survival. This study examines the effects of burial depth and application of soil amendments on seedling emergence under different watering regimes on four semi-arid zone species. The soil amendments used were hydrogel (EarthCare Water Crystals), fertiliser (Osmocote), and a commercial soil microbial inoculant (Bactivate5). It was found that, while heavier seeded species were able to emerge from deeper below the soil surface, all seeds in the study preferred to emerge from shallow burial depths of around 6–10 mm. Soil amendments were shown to have minimal effect on emergence rates, regardless of the watering regime, while the watering regime was found to have the largest impact. Seedlings under a low watering regime (30% water holding capacity) were found to have the lowest emergence rate, while a moderate watering regime (55% water holding capacity) produced the highest emergence across most species. Results obtained from this study suggest that shallow burial of seeds 6–10 mm below the soil surface, as opposed to surface placement or deeper burial, may enhance emergence for the species tested. Although the soil amendments did not improve plant species emergence, amendment application may still be beneficial for developing seedlings by enhancing seedling resilience to adverse growing conditions such as moisture stress or extreme temperatures.