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)

3623 E. American Avenue Oak Creek, WI 53154

8.2 meters, 160 degrees

22.73

1036 Illinois Street

Racine, WI 53405

4.9 meters, 132 degrees

113.64

6511 Greenridge Drive

Racine, WI 53406

7.6 meters, 10 degrees

22.73

1802 Park Avenue

Racine, WI 53403

2.9 meters, 23 degrees

113.64

405 W. Boulevard

Racine, WI 53405

5.0 meters, 73 degrees

45.45

2051 Brogham Lane

Racine, WI 53404

6.3 meters, 197 degrees

22.73

3625 E. American Avenue

Oak Creek, WI 53154

8.1 meters, 96 degrees

22.73

2423 Harrison Avenue

South Milwaukee, WI 53172

5.6 meters, 275 degrees

45.45

1124 Virginia Street

Racine, WI 53405

6.3 meters, 58 degrees

45.45

1932 Linderman Avenue

Racine, WI 53405

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)

1514 Wisconsin Avenue

Racine, WI 53403

9.7 meters, 232 degrees

22.73

504 W. Boulevard

Racine, WI 53405

12.3 meters, 12 degrees

22.73

1508 S. 15th Avenue

South Milwaukee, WI 53172

16.8 meters, 69 degrees

11.36

429 Shelley Drive

Racine, WI 53405

9.9 meters, 165 degrees

22.73

1709 Rapids Drive

Racine, WI 53402

3.2 meters, 87 degrees

11.36

1906 Mars Avenue

Racine, WI 53402

4.7 meters, 63 degrees

45.45

2200 Douglas Avenue

Racine, WI 53402

9.9 meters, 220 degrees

22.73

2836 Osbourne Boulevard

Racine, WI 53405

11.1 meters, 209 degrees

45.45

2524 W. Abbott Avenue

Milwaukee, WI 53221

6.6 meters, 130 degrees

11.36

431 Shelley Drive

Racine, WI 53405

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.