Lauren G. Melcher and Emily A.
Rinaldi, authors
Ms. Laurie Rosenberg, editor
Our instructor, Ms. Rosenberg gave us an overview of the challenges that face the hillside - invasive species, particularly Asian honeysuckle, a steep 12-18% slope according to the Guidelines for Soil Quality Assessment in Conservation Planning (2001), and excess run-off water not absorbed by pavement that is directly behind the hillside.
Since soil qualities contribute to the overall health of an ecosystem, and with these challenges in mind, we wanted to learn everything we could about the environment of the hillside and how to improve the tough situation. We created this soil quality project to document the current baseline status of the health of our environment, to guide us in discovering how to maintain it or improve it.
As a secondary goal, we wanted to study the soil without using expensive scientific equipment or elaborate procedures that might be out of reach for the average land steward. Our intent was to model methods of gathering relevant information about soil quality using ordinary tools that anyone can easily acquire and use. These tests and methods can then be easily replicated by others who come after us. Fortunately, the United State Department of Agriculture has an extensive free manual on field methods of studying and evaluating soil quality. We used this handbook as our primary guide for this task.
We conducted several tests to figure out key characteristics of our soil, like the pH, the nitrogen, phosphorous and potassium content, the organic matter content, the bulk density, the electro-conductivity, and the aggregate stability. These results will help us determine a starting point for our soil and what we need to do to improve the soil and the hillside. The following paragraphs describe our methods- what we tested, how we tested it and why we tested it.
Soil Profile:
We visited the Hillsdale Conservation District where Nathan
McNett assisted us in identifying the type of soil we have at our specific
hillside in the Slayton Arboretum. We determined this by looking at the United
States Department of Agriculture’s Soil
Survey of Hillsdale County, Michigan. The soil survey guide contains information
about soil properties and qualities, as well as the use and management of the
land. This helps inform the reader about what steps they need to take to
improve the land based on what they have to work with. Based on the map, our
soil is a “fox gravelly sandy loam” which is susceptible to erosion. The 12-18
percent slope and the irregular oval shape of the land furthers the chances that the site might have an erosion
problem. If the soil is disturbed and vegetation is removed, then the problem
may become serious.
pH
Determining the pH of the soil is
important because it tells us the relative acidity or alkalinity of the soil,
which can give us insight into why or why not specific plants grow on the
hillside. To obtain an accurate pH, we used two different test kits from AccuGrow and Solvita, and we ran each test twice. To perform the tests, we
gathered some soil samples and tried to get a good mixture of the top few
horizons, not just one layer. Then, put soil in a test tube about halfway full,
and add distilled water to the tube filling it almost to the top. Then, shake
the test tube vigorously for 30 seconds, and allow the large particles to
settle to the bottom. This settling decreases the chance of inserting the pH
strip into the soil particles, which might affect the pH and give us an
inaccurate value. It also interferes with the
test readers ability to see and read the colors accurately, with soil particles
attached to the pH paper. Once the soil was settled, we inserted the pH strip
into the top of the test tube water and immediately removed it from the sample
to compare the color on a chart. The two AccuGrow tests read a pH of 8, which
is alkaline. We then performed several Solvita tests and got pH values of 6, 7
and 6.5, which was more in line with what we would expect for our type of soil.
Averaging these pH values came to about a 6.5-7 depending on if we included
both tests, or just the Solvita tests. Invasive species like honeysuckle, do
not thrive as well in acidic soils, they prefer slightly alkaline soils. Our
soil is on the borderline between neutral and acidic. More sensitive tests may be needed in the
future to detect finer levels of pH variance between 6.5 and 7 or between 7 and
8.
Nitrogen,
Phosphorus, and Potassium content:
The balance of nitrogen, phosphorous, and potassium in the
soil is vital to the growth and success of the plants. We tested the
concentration of these three macronutrients by placing distilled water and a
small soil sample into a test tube. Then shake the tube and let the soil settle.
Once settled, transfer five drops of the Solvita test kit drops for each
element into the test tube, cap, and shake the solution for ten seconds. Again,
wait for the soil to settle before placing the strip into the solution. Once
you dip the provided strip, remove it immediately and wait for it to dry. Then
compare the color on the strip with the color on the chart on the bottle. These
values give us an idea of what our nitrogen, phosphorus, and potassium contents
are in the soil. Our nitrogen content came out to be “A” which is the lowest
amount on the chart. This means we do not have a lot of nitrogen rich organic
matter in our soil. This makes sense because of the soil’s gravel pit history,
the water runoff and erosion problem that leaches the soil of nutrients, and
the lack of herbaceous trees and plants currently on the hillside. Our
phosphorous content was at a very high “D” level. Since the site is adjacent to a runoff area,
sediment and runoff could be carrying phosphorous onto the land, or other
factors could be influencing the phosphorous content. The potassium level was at a moderate, “B”
level.
Bulk Density:
Bulk Density is an important test to determine the density
of our soil, which tells us how compacted the soil is. According to the Soil
Quality Test Kit Guide (2001), collect several soil samples with a soil corer
to try to get different horizons of the soil included in the test. Then,
separate a small amount of soil, we did about ⅛ cup, and sift the large rocks
and particles out. This will give you a clean soil sample and the maximum soil
content. Our first soil sample weighed 28 grams. Then place the sample into a mug;
ours weighed 348 grams, which will affect our calculations later. Then
microwave the soil with three cycles of four minutes intervals on high power,
or until the weight of the soil stops decreasing after every heating. Heating
the soil evaporates all of the water out of the soil, which is necessary for
the bulk density test. Once the weight of soil holds constant, we know the soil
is dry. Using these values, we can calculate the bulk density, soil water
content, and the soil water pore space.
General relationship of soil bulk
density to root growth based on soil texture
|
|||
Soil Texture
|
Ideal bulk densities for plant growth
(grams/cm3)
|
Bulk densities that
affect root growth
(grams/cm3)
|
Bulk densities that
restrict root growth
(grams/cm3)
|
Sands, loamy sands
|
< 1.60
|
1.69
|
> 1.80
|
Sandy loams, loams
|
< 1.40
|
1.63
|
> 1.80
|
Sandy clay loams, clay loams
|
< 1.40
|
1.6
|
> 1.75
|
Silts, silt loams
|
< 1.40
|
1.6
|
> 1.75
|
Silt loams, silty clay loams
|
< 1.40
|
1.55
|
> 1.65
|
Sandy clays, silty clays, clay loams
|
< 1.10
|
1.49
|
> 1.58
|
Clays (> 45% clay)
|
< 1.10
|
1.39
|
> 1.47
|
Figure 1. Shanstrom, N. (2014)
Unfortunately, our tests did not go very well. Our mug
shattered in the microwave seven seconds before the end of our second round of
heating, so we were not able to calculate accurate values for bulk density. We
tried to work with what soil we had, and used coffee filters to hold the soil
instead of our mug. We lost some soil in the microwave, even after cleaning it
up, and some glass pieces from the mug got in our soil sample, and although we
picked out everything we could see, some glass pieces may have affected the
weight of our soil. Based on what was left, and adjusted the soil sample to ⅛
cup instead of our whole sample tested, we got a bulk density value of 0.778
g/cm3, soil porosity of 0.706%, soil H2O content from 28
grams of soil, was 5 grams of water, and the volumetric H2O content
was 3.89 g2/cm2. These values may not be highly accurate,
but they give us an idea of a small sample of soil bulk density and what it
could mean for the hillside.
Electro-conductivity:
Electro conductivity is the ability of a substance, in our
case soil, to conduct an electrical current. This is important for soil to be
able to do because it helps with the processes of respiration and decomposition
by microbes, fungi, etc. in the soil. There is
an exchange of ions, which is part of the metabolic processes mentioned above.
Our soil is considered a sandy loam, which means it has a high sand content.
Sand has the lowest conductive abilities between clay, silt and sand, which
means our soil will likely have a low conductivity value. The soil on the
hillside may also be different from soil elsewhere in the arboretum. We used a ›HI 98331 Direct Soil Conductivity
and Temperature Meter to measure our sample’s conductivity. To perform the
test, place a soil sample in a cup and wet it. The meter must go down into the
soil sample at least one inch, but also be above the bottom of the cup at least
one inch, so the cup does not interfere with the measurement. We tested our
sample three times and our value every time was 0.25 mS/m. According to USDA
Soil Electrical Conductivity (see references) and the Soil Quality Test Kit
Guide (2001), this value means that our soil has low conductivity, but this
makes sense based on the sandy texture of the soil.
Soil Infiltration:
The purpose of soil infiltration is to measure the soil’s ability for water to move through it and how quickly the water moves through. If the soil is more porous, then water will more easily pass through it, but if the soil is compacted and hard, then it is more difficult for the water to soak down through the soil. This test is directly tied to bulk density, and the results of both tests should reflect similar results. To perform this test, get a six-inch diameter, five-inch high steel ring and a wood block. Find a relatively flat surface with sparse vegetation and rocks, clean off vegetation and rocks if any. Then, place ring into soil as hard as you can to push it down into the soil. Then press/hammer the ring into the soil three inches deep. Next, gently press the edges of the soil within the ring to get an accurate reading of the soil’s ability to infiltrate water. Then place a sheet of saran wrap over the ring, making sure to cover it completely, and add 444 mL of water over the saran wrap. With the timer ready, quickly remove the saran wrap, allowing all of the water to fall upon the soil instantly and start the timer. Do not pour the water directly onto the soil because the soil will absorb the water unevenly, and we are testing the whole ring of soil’s infiltration rate. Record the time until the water is just glistening at the surface and around the edges. This test was very difficult because our soil is rocky and compact. Our infiltration rates were considered healthy. Our first test took 3 minutes and 50 seconds for the water to soak down, and the second test took 10 minutes and 44 seconds to soak down. These varied results in a small sample size need to be repeated for more accuracy. However, our results are within the expected parameters for a sandy soil, according to the USDA Soil Quality Test Kit SECTION II Background & Interpretive Guide for Individual Tests.
The purpose of soil infiltration is to measure the soil’s ability for water to move through it and how quickly the water moves through. If the soil is more porous, then water will more easily pass through it, but if the soil is compacted and hard, then it is more difficult for the water to soak down through the soil. This test is directly tied to bulk density, and the results of both tests should reflect similar results. To perform this test, get a six-inch diameter, five-inch high steel ring and a wood block. Find a relatively flat surface with sparse vegetation and rocks, clean off vegetation and rocks if any. Then, place ring into soil as hard as you can to push it down into the soil. Then press/hammer the ring into the soil three inches deep. Next, gently press the edges of the soil within the ring to get an accurate reading of the soil’s ability to infiltrate water. Then place a sheet of saran wrap over the ring, making sure to cover it completely, and add 444 mL of water over the saran wrap. With the timer ready, quickly remove the saran wrap, allowing all of the water to fall upon the soil instantly and start the timer. Do not pour the water directly onto the soil because the soil will absorb the water unevenly, and we are testing the whole ring of soil’s infiltration rate. Record the time until the water is just glistening at the surface and around the edges. This test was very difficult because our soil is rocky and compact. Our infiltration rates were considered healthy. Our first test took 3 minutes and 50 seconds for the water to soak down, and the second test took 10 minutes and 44 seconds to soak down. These varied results in a small sample size need to be repeated for more accuracy. However, our results are within the expected parameters for a sandy soil, according to the USDA Soil Quality Test Kit SECTION II Background & Interpretive Guide for Individual Tests.
Aggregate Stability:
An aggregate is a chunk of soil that is held together well and not crumbling too much. Aggregates are held
together by organic compounds in the soil that help the soil retain moisture
and nutrients. Even with our sandy soil
we were able to get some sizeable chunks of soil and test the aggregate
stability. We created an aggregate stability test kit by bending a wire rack to
fit halfway down into a plastic cup, and then filled the cup, covering the wire
rack, with water. Then we placed the chunk of soil on the wire rack submerged
in water and started the timer. We wanted to see how long it took the aggregate
to come apart in the water. After 20 minutes the aggregate had barely fallen
apart, so we decided to leave the aggregate over the weekend and check on its
progress on Monday. After three days the aggregate still had not come apart!
This is surprising, with a sandy soil, but is very good news for us. With
aggregates that hold together very well, the soil will not slide off the
hillside as fast or easily, so our erosion problem could be a lot worse. This
soil would be able to hold a rain garden and water very well, which is one of
our solutions to this erosion problem.
Ms. Rosenberg came up with the idea of putting in a rain garden to solve both the erosion and plant life restoration problems. This solution helps the environmental aspect of controlling erosion, as well as making the hillside look more pleasant for visitors. We will create this rain garden using rich compost soil, plants that hold soil and gravel well and absorb a lot of water.
Our solutions to the outlined include building a raingarden
to control erosion and absorb excess run-off water, to introduce more plants
and different vegetation (non-invasive) to help with the weeds and honeysuckle
problem and to sparingly spread compost to help enrich the soil. Compost will
be the ideal medium to enrich the soil because it will slowly increase the
quality of the soils and not dramatically change the conditions that might lead
to further invasion by invasive species.
We hope that the Fall 2016 Environmental Stewardship class will take our
recommendations and look into designing a rain garden and continue to manage
the invasive species.
Works Cited
A Soil Information. (n.d.). Retrieved December 9, 2015, from
http://www.windhamraymondschools.org/biosite1/soil_information.htm
EC (Electrical Conductivity). (2015). Retrieved December 8,
2015, from http://geoprobe.com/ec-electrical-conductivity
Guidelines for Soil Quality Assessment in Conservation
Planning. (2001). Retrieved December 9, 2015, from http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_051259.pdf
Perkis, W., & Bowman, W. (1997). Soil survey of Hillsdale County, Michigan. Hillsdale, Michigan:
United States Department of Agriculture.
Projects. (2014). Retrieved December 9, 2015, from http://ecosystemllc.com/projects/
Rosenberg, L. (2015, October 29). Homeland Stewardship Part
1. Retrieved December 9, 2015, from http://www.lpinkmountain.blogspot.com/
Shanstrom, N. (2014, October 6). SubscribeGreen Infrastructure.
Retrieved December 8, 2015, from
http://www.deeproot.com/blog/blog-entries/the-most-important-factor-for-growing-healthy-trees-2
Soil Electrical Conductivity. (n.d.).
Retrieved December 7, 2015, from http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_053280.pdf
Soil Quality Test Kit Guide. (2001, July 1). Retrieved
December 7, 2015, from
http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_050956.pdf
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