Effect of Dog Feces on Soil Nitrate
Content
October 25, 2006
Abstract
For our research, we wanted to know if the nitrate
content of soil would be greater in the yards of dog owners versus those yards
of people who do not own pets. Testing areas using a random method, we found
that yards that support dogs contain a higher level of nitrates than yards that
do not support dogs. This finding supported our hypothesis, and the results
were significant. Our P-value for this experiment was 0.015. After analyzing
our results, we found that when dogs defecate, nitrogen is cycled through their
bodies and put back into the environment, which results in a higher nitrate
content in the soil.
Keywords: nitrate, defecation, dog
Introduction
We conducted this experiment to find
out whether or not having a dog, Canis
familiarus, influences the amount of nitrate that is contained within the
soil in the yard where the dog lives. Our stimulus for this research was
discovering that nitrogen in animal waste is the third leading contributor of
nitrate discharge, following behind agricultural biotic nitrogen fixation and
atmospheric deposition of nitrogen. Also, animals release a significant amount
of nitrogen as atmospheric ammonia, which returns to the soil through wet or
dry deposition, and eventually is converted into nitrates through the process
of nitrification, which is completed by bacteria decomposers (Jordan, Weller,
1996). For our experiment we tested the hypothesis that urban yards that
support dogs have higher nitrate levels than urban yards that do not support
dogs.
Materials and Methods
On September 15, 2006, between the hours of 10 a.m.
until 5:30 p.m., we gathered soil samples from twenty different yards; ten of
those yards belonged to dog owners, and ten yards belonged to people who do not
own dogs. The materials that we used during this experiment are as follows: a
Kesson Graduated Metric Tape Measure, model OTR5OM, an A-1000 Suunto compass, hand-made
paper plate Frisbee, and a Lamotte Combination Soil Testing Kit, model SPH-14.
We started by determining which yards supported dogs and which did not by
making a list of each based on people that we knew. At each location we randomly determined a
testing site by tossing a Frisbee from the back door of the house. We recorded
each location within the yard by using a compass and a tape measure to
determine the distance and direction away from the yard-owner’s back door.
Then, we took a sample of the soil directly beneath where the Frisbee landed by
using a 0.5 mL soil scoop. We took three scoops of soil and placed it into a
test tube labeled with the location. All soil samples were taken back to our
house to conduct and analyze the tests.
Before we could begin to test the nitrate
level we had to perform an extraction procedure on the soil, which consisted of
three main steps. First, we filled an extraction tube with 14 mL of Extracting
Solution. Second, we added the soil to the solution, placed a cap on the test
tube, and shook the test tube for one minute. Last, we filtered the soil
suspension into another test tube by using a funnel and filter paper. We
repeated this procedure with all twenty of our samples. After the extraction
process, we were able to test the nitrate level.
The procedure for determining the
nitrate level in the soil sample consisted of four steps. The first step was to
transfer 1 mL of the soil extract to a spot plate by using a 1 mL pipette.
Next, we added 10 drops of Nitrate Test
Reagent #1 to the soil extract. Then, we added 0.5 grams of Nitrate Reagent #2 to the soil extract
solution. Lastly, using a clean stirring rod, we stirred the solution and
allowed it to process for five minutes before reading the results. We read and
recorded the results of the tests by comparing the colors of the solutions to a
Nitrate Nitrogen Color Chart.
Results
Table 1 shows the nitrate levels in all twenty yards.
Figure 1 shows that the average nitrate level in yards with dogs was 52.27
kilograms per hectare, while the nitrate level in yards without dogs was 22.73
kilograms per hectare. The standard deviation for the yards with dogs was 31.3,
whereas the standard deviation for the yards without dogs was 11.5. A T-test
was also conducted which resulted in a P-value of 0.015, which is statistically
significant.
|
Address of Dog Owners |
Location in Yard (from back door) |
Nitrate Level (kilograms per hectare) |
|
|
8.2 meters, 160 degrees |
22.73 |
|
|
4.9 meters, 132 degrees |
113.64 |
|
|
7.6 meters, 10 degrees |
22.73 |
|
|
2.9 meters, 23 degrees |
113.64 |
|
405 W. Boulevard |
5.0 meters, 73 degrees |
45.45 |
|
|
6.3 meters, 197 degrees |
22.73 |
|
|
8.1 meters, 96 degrees |
22.73 |
|
|
5.6 meters, 275 degrees |
45.45 |
|
|
6.3 meters, 58 degrees |
45.45 |
|
|
6.0 meters, 210 degrees |
68.18 |
|
|
|
Average: 52.27 |
|
Address of Non-Dog Owners |
Location in Yard (from back door) |
Nitrate Level (kilograms per hectare) |
|
|
9.7 meters, 232 degrees |
22.73 |
|
504 W. Boulevard |
12.3 meters, 12 degrees |
22.73 |
|
|
16.8 meters, 69 degrees |
11.36 |
|
|
9.9 meters, 165 degrees |
22.73 |
|
|
3.2 meters, 87 degrees |
11.36 |
|
|
4.7 meters, 63 degrees |
45.45 |
|
|
9.9 meters, 220 degrees |
22.73 |
|
|
11.1 meters, 209 degrees |
45.45 |
|
2524 |
6.6 meters, 130 degrees |
11.36 |
|
|
4.9 meters, 10 degrees |
11.36 |
|
|
|
Average: 22.73 |
Table 1. Location of each test and the results
of each site
Figure 1. Nitrogen Content
of the Soil in Yards Without Dogs versus Yards With Dogs
Discussion
Our results supported our hypothesis. We discovered
that dog-owners’ yards had a higher level of nitrate content than
non-dog-owners’ yards. One study found that 40% to 70% of nitrates are excreted
in the dog’s urine and the remainder of it is in the feces (Zeballos et al,
1995). This supports our findings that larger amount of nitrogen could be found
in dog-owner’s yards, as a result of nitrates being introduced into the soil through
defecation. Also, animal feces break down naturally into the soil, and do not
amount to hazardous nitrogen conditions because it is a biodegradable organic
compound. The levels of nitrates that occur in the soil are influenced by the
amount of available oxygen for bacteria to use during decomposition, the amount
of leaching due to precipitation, and the temperature of the environment. When
there are large levels of nitrates in the soil, they can be leached into the
groundwater or absorbed in rainwater runoff, which creates potential hazardous
conditions for human and animals if ingested. When nitrates are reduced to
nitrites in the body, they have the ability to oxidize hemoglobin in the blood which
creates difficulties in the transport of oxygen in the blood (Loehr, 1978).
If we were to conduct this experiment again, we would
make sure to do it after a significant amount of time has passed, approximately
five to seven days, since precipitation has occurred. We would do this so that
the nitrates would not be leached from the upper horizons of the soil, and we
would be able to get a more accurate measurement of the nitrate levels in the
soil.
LITERATURE CITED
Jordan,
T., Weller, D. (1996). Human Contributions to Terrestrial Nitrogen Flux.
Bioscience,
46, 655-654 Retrieved September 23,
2006 from JSTOR database.
Loehr,
R. (1978). Hazardous Solid Waste from Agriculture. Environmental Health
Perspectives,
27, 261-273, Retrieved September 23,
2006 from JSTOR database. Zeballos, G., Bernstein, R., Thompson, C., Forfia,
P., Seyedi, N., Shen, W., Kaminski, P.,
Wolin, M., Hintze, T. (1995). Pharmacodynamics of
Plasma Nitrate/Nitrite as an Indication of Nitric Oxide Formation in Conscious
Dogs. Circulation, 91, 2982-2988.
Retrieved October 25, 2006 from Google Scholar.