Research Towards an Engineered Urban Soil for Trees and Other Ecosystem Services.

The landscape industry has become increasingly reliant on engineered soil mixes for tree plantings. These soil mixes are often composed of coarse sand, aggregates, compost and screened top-soil. These mixes are intended to provide adequate nutrient supply and drainage at specified densities. Mix specifications have mostly evolved from the athletic turf industry, and they may not work for trees. Furthermore these current mixes may not be optimized for other important urban ecosystem services such as storm-water retention and carbon sequestration. This research will highlight findings from field and greenhouse experiments on new engineered soil mixes that are optimized for trees and other ecosystem services. The new soil mixes being tested include less sand, more un-screened top-soil soil and organic amendments (biochar and bisolids). Preliminary analyses have found significantly greater tree growth and health, carbon sequestration in soil and reduced volumes and nutrient contents of leachates with these mixes compared to the traditional engineered soils.