Organic amendments decrease bulk density and improve tree establishment and growth in roadside plantings

Abstract Soil compaction significantly impacts urban tree survival and herbaceous vegetation recruitment along roadsides. Soil samples were collected at two highway tree planting sites in Ontario, Canada. The average soil bulk density in the 0–10 and 20–30 cm range was 1.45 g cm −3 and 1.55 g cm −3 , respectively, at Site 1. At site 2, the average soil bulk density in the 0–10 and 20–30 cm range was 1.49 g cm −3 and 1.67 g cm −3 , respectively. Six treatments were established on each site to determine the amount of organic amendment required to decrease bulk density and increase tree growth as a measurement of successful tree establishment. Compost was incorporated into the soil at 0%, 10%, 25% and 50% on a volume-to-volume basis at both sites. In 2014 Acer x freemanii Autumn Blaze ® ‘Jeffersred’ whips were planted into each treatment bed (Site 1, n = 36 and Site 2 n = 42). Bulk density, porosity, soil pH, EC, tree survival, height, shoot extension and chlorophyll content were measured for the 2014 and 2015 growing seasons. Incorporation of 25% v/v compost consistently decreased bulk density to below-root restricting thresholds, resulting in improved tree growth. Significant differences were observed in chlorophyll content between organic-amended remediated treatment beds compared to the control; chlorophyll content was significantly higher (p