How
is soil quality affected by soil management?
By Aurora, Eleanor Roosevelt High School, Greenbelt, MD
Introduction
Soil is one of our most precious natural resources, as it
integrates all parts of the ecosystem.
It provides a medium for plant growth so that we can have
food, clothing, and other materials. Soil filters water, decomposes
waste, stores heat, and exchanges gases. Soil is alive- it
is the home to billions of micro- and macroscopic organisms.
It is a material used for construction, medicine, and art.
It produces a snapshot of the geologic, climatic, biological,
and human history at the place that they are found. Unfortunately,
there is a limited amount of soil that can actually be used
for growing food, and all of the other uses that we require
it for. When improperly managed, soil can become eroded, polluted,
or destroyed. It can also cause damage to other parts of the
ecosystem.
Humans have used soils since we have been on the Earth. In
the 1930's, technology caught up with us. After the war, we
had leftover chemical bombs, weapons, and oils which we could
not use. So, companies took theses bombs, weapons, and oils
and processed them into chemical fertilizers*
and pesticides* which were then
used in our soils to eradicate the pest population and to
help to fertilize the soils. One of the most popular chemical
compounds used at the time was anhydrous ammonia, a petroleum-based
pesticide which was fatally toxic if it made contact with
the skin, eyes, and lungs. It also was slowly disintegrated,
so the unused portions of it were found in streams and rivers,
and was later discovered to produce air pollution and made
a large contribution to the widening of the hole in the ozone
layer. As time went on, the chemical fertilization and pest
control phase grew. By the early 1950's, all of the fruits
and vegetables grown in our country were treated with man
made chemicals such as treflan, parathylon, DDT, and 424D-
all toxic to the human system (Adams, 1986). By this time,
chemical farming had become very, very popular and so had
gained the name "conventional
agriculture*." There are a few benefits to conventional
agriculture, such as that it allows farmers to grow the same
crop in the same place every year, which is convenient for
farmers because crop rotation*
requires uprooting all plants and starting new in different
place (until the soil becomes degraded), and that it treats
soil with a few elements (i.e.: nitrogen, potassium, phosphorus)
which may have been depleted by farming (Brady and Weil, 1996).
It had been proven to cause soil
degradation*, which would make it easier to be effected
by erosion*. Some methods in conventional
agriculture have led to the removal of 15-20 tons of top
soil* per acre annually, and now scientists estimate that,
if we continue with conventional agriculture, in 40-50 years,
there will be no more top soil left in the world (Miranda,
1995). Another problem also arose from conventional agriculture-
although the bugs and pests that were specifically targeted
were killed, the chemical compounds that were used often attracted
other, unanticipated bugs and pests, and caused some of the
targeted pests to adapt and become tolerant of the pesticides
(Miranda, 1995).
While more than half of the world is using conventional agriculture
to grow crops, there is a new, more radical approach to farming-
organic farming*. Although
organic farming is a fairly recent idea in our society, it
had been used before by our ancestors. The principle behind
organic farming is to grow crops completely without using
man-made chemicals, and to help to nourish the earth while
also gaining something from it (namely, strong healthy crops).
Organic farming is very beneficial, both to the soil and to
us. Using organic farming, the soil maintains its structure,
consistence,* and diversity*
of life within the soil (both micro- and macroscopic life),
which is considered very important in a healthy soil. It also
allows farmers to grow many crops in the same area, which
provides diversity for the soil and also is a natural way
to keep out pests. By organically treating the soil with compost*
and with animal manure, the soil stays healthy and also is
enriched so that any tillage* of the
soil will not harm it in the long run. Also, the organic material
supplied to soil through organic farming serves as a sponge
to water, and helps to store nutrients (Federation of Ohio
Naturalists, 1995).
The idea of chemical vs. organic farming is the main reason
for this project. By looking at conventionally-treated, organically-treated,
and forested soil of the same type, the question of whether
different management practices affect the soil will be addressed.
This question will be answered by comparing a) the chemical
composition of all three soils (i.e.: pH, nitrate nitrogen,
potassium, phosphorus, etc.), b) the consistence, c) the texture,
d) the soil structure*, e) the
color, f) the macro invertebrate activity, and g) the bulk
density. The soils that will be tested are in the Mattapex
soil series. Both the soil that
is cultivated and the soil that is farmed with compost have
been farmed from 1985-1992 with alfalfa, and from 1993-1995
with no-till corn. The cultivated soil, starting in 1996,
has been farmed with corn and has been treated with commercial
fertilizers and herbicides. The composted soil, also starting
in 1996, has been farmed with corn and treated with chicken
manure and compost- a total of 4 tons per acre per month.
Soil Vocabulary
and Definitions
Color Wheel- a color description
of the different possible colors of soil- the soils are titled
with letters that represent the actual color of the soil,
and by numbers which represent the intensity of the color
of the soil
Compost- organic residues that
have been piled, moistened, and allowed to undergo biological
decomposition
Consistence- a description
of how easily a soil breaks apart when pressed- can be friable,
which means that it breaks apart easily, or firm, which means
that it takes a lot of pressure for the soil to break apart.
Conventional Agriculture-
the popular term for tillage practices and application of
chemicals
Crop Rotation- a planned
sequence of crops growing in a regularly recurring succession
on the same area of land
Diversity- the presence of
many different organisms in a soil
Erosion- the wearing away of
the land surface by water, wind, ice, or other geological
agents
Fertility- the quality of
a soil that enables it to provide essential chemical elements
in quantities and proportions for the growth of specified
plants
Fertilizers- any organic
or inorganic material of natural or synthetic origin added
to a soil to supply certain elements essential to the growth
of plants
Munsell Soil Color Book- a handbook
which displays the possible colors of soil and titles each
one according to their place on the Color
Wheel
Organic Farming- farming
without the use of man made chemicals and using only organic
matter which helps to enrich the earth at the same time as
it helps in producing crops
Organic Matter- any dead
matter within the soil of a natural origin (e.g.: compost)
Pesticides- any material
added to the soil in order to eradicate existing pests and
insects and to prevent the recurrence of any new pests or
insects
pH-the negative log of the hydrogen
ion concentration which is an indicator of how acid or basic
the soil is. The lower the number, the more acidic. The scale
runs from 0-14, with 7 being neutral.
Soil Degradation- a
decrease in the productive capability of the soil (e.g.: erosion
or compaction)
Soil Quality- the capacity
of a specific kind of soil to function, within natural or
managed ecosystem boundaries, to sustain plant and animal
productivity, maintain or enhance water and air quality, and
support human health and habitation
Soil Series- the finest
level of classification consisting of soils that are similar
in all major profile characteristics
Soil Structure- the combination
or arrangement of primary soil particles into secondary particles,
units, or peds ( the shape of the soil units). Some types
of structure are granular (which looks like cookie crumbs),
blocky (which looks like small blocks), prismatic (which is
prism shaped). Grades of structure are weak, moderate, or
strong depending on how easy it is to distinguish the type
of structure.
Soil Texture- the way the
soil feels, based on the amount of sand, silt, and clay present
in the soil
Tillage- the mechanical manipulation
of soil for any purpose (e.g.: crop production)
Top Soil- the layer of soil
on the surface of a soil- typically considered to be the most
fertile section of a soil
Problem Statement
How is soil quality affected
by soil management? Is there a difference in soil quality
between the same soil type which has been forested, farmed
conventionally, and farmed using compost? If so, what?
Hypothesis
The quality of soil will be affected by the use of conventional
farming. Soil properties which control soil quality such as
soil structure, organic matter
content, earthworm activity, and other properties will be
different from the unmanaged soil or the soil treated organically.
Fertility may be higher in the conventionally
treated soil than in the other types of soils because of the
addition of fertilizers.
Materials
- unmanaged soil such as a forest (control group)
- agricultural field to which pesticides and fertilizers
have been added (conventional farming)
- agricultural field to which compost has been added
- LaMotte Soil Testing kit (N, P, K)
- PG County Soil Survey Report
- liter-sized plastic bags for each site and marker
- newspaper for drying soil on
- 250 mL. can for sampling (3 for each site)
- nail and hammer for poking a hole in the bottom of each
can
- experts from the Beltsville Agricultural Research Center
(BARC) and NASA
- scale for weighing soils
- Munsell soil color book
- pH pen and buffers
- trowel for gathering samples
- sieve
- 100 mL beakers
- 100 mL graduated cylinder
- distilled water
Procedures
The procedure for the completion of this project is as follows:
Step 1: Find 3 soils of the same soil type of which one has
been conventionally farmed, farmed with compost but with the
same farming history, and one that has been forested.
Step 2: Collect 3 surface samples
from each site, each filling a 250 mL can
Step 3: Carefully observe soil properties (such as structure,
consistence, earthworm activity, and color) in the field.
Structure, consistence, and earthworm activity is tested by
simple observation and by feeling the soil's texture and consistency.
Color is tested by comparing a sample of moist soil to the
colors displayed in the Munsell Soil Color Book (see "Introduction
to Science Project, pt. 2"). Step
4: Take samples back home, and dry them, sieve them, and
test them for the following chemical properties: pH, nitrate
nitrogen (N), phosphorus (P), potassium (K). pH will be tested
using a pH pen, calibrated with buffers.
The nitrogen, phosphorus, and potassium will be tested using
a LaMotte soil testing kit. The
LaMotte soil testing kit has materials to extract solution
from the soils containing the elements to be tested. Reagents
for each of these are then used to change the color of the
extracted solution to compare with color charts that tell
the relative amount of each nutrient in the soil. pH will
be tested for because acidic soils can be harmful to plants,
and controls the presence of other nutrients in the soil.
Therefore, the soils can be partially proven harmful or helpful
to plant growth by testing pH. Nitrate nitrogen, phosphorus,
and potassium are nutrients that are important for plant growth,
and may be affected by different soil properties.
Results
pH Test Results
The results of the pH tests in the three differently managed
soils were varied. In the composted soil, the pH was at three
different levels- in sample one, it was 7.1, in sample two,
it was 6.4, and in sample three, it was 6.8. The levels of
pH in the chemically cultivated soil were are different levels
as well, although not quite as disparately- in sample one,
it was 6.6, in sample two, it was 6.7, and in sample three,
it was again, 6.6. In the forested soil, the pH levels were
again varied- in sample one, it was 6.6, in sample two, it
was 6.8, and in sample three, it was 5.5.
Click the thumbnail to see a graph of the average pH results:
Chemical
Test Results (NPK Tests)
The soils were tested for three different chemicals in this
series of tests. The results for the levels of nitrate nitrogen
in both the forested and the composted soils were all the
same- there was no nitrogen in the soils. In the cultivated
soil, there was a larger amount of nitrogen in the soil, but
still not a very large amount. The results for the levels
of phosphorus in the soils were again, all very similar. In
both the composted and the forested soils, there was a small
amount of phosphorus present. In the chemically cultivated
soil, there was also, for the most part, a small amount of
phosphorus present, but in sample two of the cultivated soil
there was a spike in the amount of phosphorus and the level
reached a medium amount. The results for the levels of potassium
in the soils was also quite similar between the different
soils. In the composted soil, there was mainly a medium amount
of potassium present, but, in sample two, the amount spiked
to a high level. In the forested soil, there was a medium
amount of potassium for all of the samples. In the cultivated
soil, there was also a medium amount of potassium but, like
the composted soil, the levels spiked to a high amount in
sample one.
Bulk
Density Test Results
The bulk density was different for each different soil. The
average bulk density of the composted soil was 1.04g/cm3.
The average bulk density of the chemically cultivated soil
was 1.17 g/cm3. The average bulk density of the forested soil
was .90 g/cm3.
Field
Test Results
There were several tests involved in the field testing process-
structure, color, consistence, texture, crusting, macro invertebrate
activity, and roots. The structure of the composted soil was
strong granular, as was the structure of the forested soil.
The structure of the chemically cultivated soil was medium
blocky. The color of the forested soil was the darkest- 10YR3/2
as determined by the Munsell Soil Color Book. The color of
the composted soil was next darkest- it was 10YR3/4 as determined
by the Munsell Soil Color Book. The cultivated soils were
the lightest in color- 10YR4/4 as determined by the Munsell
Soil Color Book. All three soils had a friable consistence
and a silt loam texture. Only the cultivated soil had crusting
present on its surface. Only the forested soil had macro invertebrates
(earthworms) and roots present in its contents.
Conclusions
The overall conclusion of this project was that the hypothesis,
that the quality of soil would be different in the conventionally
managed, composted, and forested soils was correct. It was
most evident in looking at the physical properties of each
of the soils. The first sign of deterioration in physical
properties was in the conventionally cultivated soil with
the presence of crusting. When a soil "crusts,"
it means that the soil is losing its structure and is forming
a crust on the surface. This is a signal that the soil will
lose its ability to let water move into it, which may lead
to soil erosion. There was no crusting on the composted or
the forested soils.
The second sign of physical deterioration in the conventionally
cultivated soil is in the color of the soil. Darkness in color
of a soil usually represents the presence of organic matter,
which is good for the soil as it allows the soil to absorb
water, improves soil structure, and adds more natural nutrients
to the soil which allow for plant growth. In comparison to
the composted and the forested soils, the conventionally cultivated
soil is the lightest in color- a 10YR4/4, as determined by
the Munsell Soil Color Book. The notation "YR."
stands for yellow-red on the Color Wheel. The number 10 in
front of the YR. stands for the hue of the soil color or its
position on the color wheel. The number before the slash is
called the "value" which has a scale of 0-10, with
0 being the darkest and 10 being the lightest. The number
after the slash is called "chroma" and it represents
the saturation of the color. This, in relation to the conventionally
cultivated soil, means that the soil is a light yellow-red
color, and both the fact that the soil is so light and that
it is yellow-red indicates that it probably has a lower amount
of organic matter which is not good for soil quality.
The third sign of physical deterioration in the conventionally
cultivated soil is in the bulk density. When a soil is dense,
it means that it is compacted and has little to no pore space
or room for the accumulation of air and water. The conventionally
cultivated soil has the greatest bulk density when compared
to the composted and the forested soil, which means that it
is more compacted, so that less air and water can not move
through it.
The second part of the hypothesis to this project was that
although the quality of soil would be different in each of
the soils, the conventionally cultivated soil would be more
fertile due to the addition of fertilizers.. This also was
proven in the experiment. The conventionally cultivated soil
was the only one of the three soils to contain nitrate nitrogen,
which, due to its negatively charged properties, is not usually
attracted to soil (soil is also negatively charged). Because
the soil doesn't hold it, it can be easily leached out the
bottom of the soil with water, taken up by plants, or changed
to different forms of nitrogen. This indicates the probable
addition of nitrate nitrogen through fertilizers which allows
the soil to have a higher fertility. Another chemical, phosphorus,
is also usually present in the soil as a negatively charged
element, and behaves in a similar way as nitrate nitrogen.
Phosphorus was found in a sizable amount in the conventionally
cultivated soil when compared to the composted and the forested
soils. The addition of phosphorus probably is also added in
the conventional soil. The only chemical component that was
present in all three soils was potassium. This is probably
because potassium is positively charged, and when is added
to the negatively charged soil, is attracted to it.
Future Study
If this experiment were to be done again, there are several
things about it that could be changed. First of all, the soil
sites could be observed over a relatively lengthy period of
time (i.e.: years). By observing the soil sites over time,
changes in soil chemistry and physical properties could be
noted, and this would add to the final data. Another thing
that could be done to improve on this project is to test the
soil for more chemicals (i.e.: sulfur, humus content, etc.).
This also would allow for more diversity in the results and
would help to make the hypothesis more easily proven or disproven.
A final thing that could be done to improve on this project
is to dig the samples at different depths, as opposed to all
at the surface. By gathering samples at different levels,
it would show whether or not the results gathered at one level
change as the soil deepens, or if the results stay the same.
Bibliography
Organic Gardening; Vol. 43, No. 4; Apr. 1996; p31-39; "Get
Your Soil Tested"
Adams, John Anthony; Dirt; Texas A&M University Press;
College Station, Texas; 1986
Federation of Ontario Naturalists; Don't Treat Soil Like
Dirt; Soil and Water Conservation Society; Ontario, Canada;
1995
Brady, Nyle C. and Weil, Ray R.; The Nature and Properties
of Soils; Prentice Hall; Upper Saddle River, New Jersey; 1996
United States Department of Agriculture; Prince Georges County
Maryland Soil Survey Report; US Government Printing Office;
USA; 1966
Thanks
To....
I would like to thank Dr. Elissa Levine (Soil Scientist)
for all of her assistance on understanding the terms and concepts
required in this project, and for being patient when I couldn't
understand what I was talking about. I would also like to
thank Dr. Laura Lengnick for assisting me in locating soil
samples and in collecting them. Thanks also go to Dr. Patricia
D. Millner for helping me locate an appropriate
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