The Comparison of Bulk Densities In Urban Landuses

1
The Comparison of Bulk Densities In Urban
Landuses
Baltimore Collaborative for Environmental
Biology
Victor O. Ukpolo Morgan State University
Dr. Richard Pouyat, Mentor U.S.D.A. Forest Service
RESULTS
INTRODUCTION     Soil is described as the
organic material of the earth's surface layer.
Its properties vary with depth and are determined
by climate, parent material, biota, topography,
and time (Kimmins, 1997). Urban soils are no
different with the exception of growing
populations and increased industrialization as
physically determining factors. For example, high
density residential, medium density residential,
low density residential, industrial,
institutional, transportation, commercial, and
forested areas are urban land uses that
physically impact soils. These land uses
introduce high traffic volumes, heavy machinery,
and other anthropogenic events that cause soil
compaction (Soane et. al. 1998). Soil compaction
has a negative effect on air and water flow
because of its degradation to porosity. Heavy
compaction inhibits plant rooting, causes water
stagnation, and decreases oxygen levels present
in the soil it is one of the most serious threats
to sustaining land use (Soane et. al. 1998).
Researchers from the Baltimore Ecosystem Study's
soil team are studying soils in the Baltimore-
Metropolitan area. Their research focuses on
making correlation's between urban land use types
and the compactness of the soils beneath them.
Figure 1.1 illustrates the bulk densities of 83
random samples taken from the before mentioned
land uses in Baltimore.   The results from these
samples are produced when bulk density is used as
an index of soil compaction. It is defined as the
weight of a unit volume of dry soil and the soil
team has made their calculations based on oven-
dried soil. They have divided the weight (mass)
of the solid particles in Mg by the total volume
of porosity and solids in m3, bulk density is
written in Mg/m3 (Soane et. al. 1998). Porosity
is essential to this equation because it affects
the percentage of air, water, and other
components found in the soil. Figure 1.2 shows
the percentage of every component normally found
in the soil. If high bulk densities are found
then researchers will expect a decline in soil
porosity that results in a decline in macro
(large) and micro (small) pores. Macro pores
function in air and water movement and micro
pores retain or hold soil moisture, they both
effect plant growth (Tan, 1996). The average bulk
density of soils falls between 1.0 and 1.6 Mg/m3
unusually high densities are indicated between
1.8 and 2.0 Mg/m3. The soil team will analyze the
bulk densities of Baltimores land uses to
determine which types have the greatest physical
impact on urban soils.  
ABSTRACT    Through urbanization, soils have been
introduced to anthropogenic related factors that
determine their physical properties. For example,
high residential, medium residential, low
residential, open urban, forested, industrial,
institutional, commercial, and transportation are
all urban land uses that physically impact soils.
Bulk density is being used as a tool to measure
the compaction of the soils found in these land
use types. Once the bulk densities are known,
then heavily compacted soils will be identified
and patterns of compaction will be seen.


Figure 1.1




DISCUSSION     Bulk density results show that
soils in high residential, industrial, and
transportation land uses located in Baltimore are
more compacted than others. These land use types
are characteristic of high traffic volumes and
heavy machinery. The results also show that
forested land uses produced higher bulk densities
than both medium and low- density residential
areas. It may be possible that urban forests that
surround these residential areas are often used
as short cuts to near by destinations therefore
they may experience more compaction. Also, the
lack of playgrounds, the abundance of side-
walks, and streets encourage children to use
urban forest as a recreational resource for bike
riding and other activities. Within these
communities, soil is most commonly found in areas
where the property is privately owned. More
people walk on sidewalks and streets. Still, one
must consider the number of samples taken to
produce these results. The Baltimore Ecosystem
Studys soil team is on track to include 150
samples to their final results. Figure 1.2
represents 83 of those and no land use has shown
indications of heavy soil compaction.

• METHODS AND PROCEDURES
• Use a bulk density hammer to extract three soil
  cores from each plot.
• Cap both ends of all cores to keep the soil from
  escaping.
• Record the wet weight of each core in grams.
• Place the cores in a Soil Oven Dryer at 1050 C
  for 24hrs.
• Than weight the cores every 30 min. until the
  weight is stabilized this will ensure total loss
  of H2O.
• Next remove the cores from the oven and take the
  dry weight of each in grams.
• To compensate for any loss in core volume.
  Measure the diameter of space between the soil
  and the core.
• Use the formula Db mass (Mg) / core volume (m3)
  to calculate the bulk densities of the soils.
• Finally, employ standard deviation to produce
  accurate averages.

• SPECIFIC AIMS
• Use the bulk density indexes to identify land
  uses with heavily compacted soils.
• To draw correlations between land use types and
  soil compaction.
•  To record bulk densities of nine urban lands use
  types in the Baltimore- Metropolitan area.

WORKS CITED   Brady, N.C. The Nature and
Properties of Soils. Mac Millian Publishing Co.
New York, 1990 J.P. Kimmins. Forest Ecology.
Prentice Hall Inc. New Jersey, 1997 Soane, B.D.
and van Ouwerkerk. Soil Compaction A Global
Threat To Sustainable Land Use. p.517. Blume,
H.P., Eager, H., Fleischhauer, E., Hebel, A.,
Reij, C., Steiner, K.G, eds. Towards Sustainable
Land Use. vol 1. Germany. 1998.