Chapter 19
Urban Soil
Problems With Urban Soils

Problems differ between Rural Growers
and Urban Soil Users


Extreme variations in soil conditions across a city
landscape


Urban more severe
Complicates landscaping
Soil moving often causes very poor soil quality
Problems (Continued)

Urban soils are improved by adding Organic
Matter such as:




Leaves
Grass Clippings
Compost
Bagged Manures
Three Traits of Urban Soil

Buried Debris

Compaction

Contamination
Buried Debris

Contractors often bury wood or masonry scraps on
the job site

Buried scraps may cause:




Restricted drainage
Excessive drainage
A physical barrier to root growth
Buried masonry, which contains lime, can raise pH
to unacceptable levels.
Compaction

Urban Soils are usually moderately to severely
compacted

Compaction can be measured by Bulk Density

At a bulk density of 1.7, roots cannot penetrate the soil

Many of our best urban trees hale from floodplains

It is possible to break up compaction if no plants
are in the way
Ways to Get Rid Of Compaction

Deep Tillage

Digging large solid particles into soil

Large amounts of Organic Matter

Wood Chips

Leaf Mold

Pave the soil with special pavers and grids that have large
holes built into them

Use Of Aerators- machines that remove vertical cores from the soil

For turf, vertical coring to six inches breaks up the soil and
makes passages for air and water movement
Soil Contamination


Deicing Salts
 Sodium chloride creates saline or even sodic soil conditions, and
chloride may reach toxic levels
 Damages plant tissue directly, especially evergreens, by
desiccation
Lead Contamination
 Lead added to paint and gasoline





Primarily effects children causing permanent brain damage, and even death
Lead found in blood can lower an IQ level by three points
Contributes to high blood pressure in adults
Main source of soil lead is automobile exhaust from cars using leaded
gas
Derelict Land
 Def- Land severely damaged by human abuse that it is unusable
without costly abatement efforts
Urban Erosion

The impact of construction site erosion differs
slightly from farmland erosion

Rilled and gullied land must be repaired before a site
can be sold

In extreme cases erosion can




Undercut roads
Collapse roads
Collapse foundations
Contributes to off-site problems
Controlling Erosion


Keep disturbed areas small
Protect disturbed areas




Keep runoff velocities low
Divert runoff away from disturbed areas
Retain sediment on-site


On steep slopes, layer of rock (rip-rap) controls erosion
Grass strips filter soil out of runoff water, as do silt fences
Establishing Vegetation


Permanent turf is the best cover, but mowing is a problem on steep hills
Hydroseeding- mixture of water, seed, and chopped hay that is blown on
a slope from the side of the road
Calculating Soil Loss

The Universal Soil Loss Equation (USLE)

Used to estimate soil losses
Predicts soil loss only from small rills and sheet erosion

Written As:


A = R K LS C P

R = Rainfall factor
K = Erodability factor – obtained from soil survey data or

calculated from USDA Handbook 537



LS = Slope factor
C = cover and management factor for bare, stripped soil
P = support practice factor (usually 1.0; few applicable)