TOOLBOX / BSLA
attract nutrients). Roots need these systems
to function and survive.
With this basic understanding of the
networking between plants and established
soils, the question is what effect building a
landscape has on these plant-soil processes?
What is the outcome of disturbing soil
(and therefore biological processes)
through stripping, stockpiling, blending,
and trucking? When creating soil for new
landscape projects, it’s unwise to ignore
the natural process created by millions
of years of biological evolution between
plants and soils. When sand, silt, and clay
have been harvested from their natural
environment with machinery, moved long
distances, then mixed and screened, this
destroys the fungal and bacterial network
of soil structure and severely damages the
natural nutrient cycling system. Common
issues resulting from disturbing soil are
self-compaction (which prevents roots
from growing freely through soil), high pH
(increase in oxygen which increases bacteria
levels which, in turn, increases pH), overwatering (contractors lack of understanding
of water movement in soils), excessive
inputs of nutrients (knee-jerk reaction to a
weak looking plant), and difficulty for plants
acclimating to a new environment. If the
natural processes of soil are so disturbed
that they can’t function, can the resulting
“product” really be called soil? And how can
soil that undergoes such rough treatment
have its functional microbial network put
back into it?
Many landscapes have engineered soil
when existing soil can’t be saved due to
constructability, contamination, or poor
quality. Often soil is non-existent on
developed project sites. Engineered soil is
focused primarily on creating the perfect
physical structure (gradation) from sand, silt,
and clay that can withstand construction
and that can control factors such as pH,
CEC, and nutrients. The primary goal is to
design a soil that will not compact during
construction and that provides nutrients
for plant growth. But when engineered
soil is installed, it is still a raw product
that is missing fully functional biological
systems. This soil has no resemblance
to the naturally created loams that have
been living with plants for years and
therefore have dynamic fungal networks
that maintain the structure of these
particles. Once this network is destroyed
in the mixing and tilling process, these soil
particles are free to move throughout the
horizons under the pressure of water (8.4
pounds per gallon) causing challenges in
developing roots.
NEAR LEFT
Pre-treating trees
at nursery prior to
delivery to build
nutrient cycling
system.
Part of what is needed to take place during
soil installation and the planting process is
to reestablish the network and the optimal
biological functions that were impacted
during the construction process. One
option is custom-blended Liquid Biological
Amendments (LBA) that allow new
landscapes to build natural soil structure
and nutrient cycling, while avoiding the
common difficulties of plant establishment
mentioned above. LBAs are custom made by
extracting the living beneficial organisms
from high quality compost and using high
volumes of oxygen and foods to reproduce
them at a quick rate for application back
into the landscapes and work to restore the
network of beneficial bacteria, fungi, and
Boston Society of Landscape Architects Fieldbook
67