Field Research Report
Comparisons of soil: Land Development soil vs. Undisturbed Soil
November 28, 2001
For this experiment the soil from four different construction sites and one control around the East Side of Milwaukee were collected. The soil samples were taken and tested for pH, nitrogen, phosphorus, and potassium. The soil was collected to study if the pH levels, phosphorus levels, and potassium levels change when they are exposed and uprooted. I compared the uprooted soil to the “undisturbed” soil from Juneau Park. Aside from slight variations in mineral levels there wasn’t much difference between uprooted soil and soil that has not been disturbed.
Key Words: pH, nitrogen, potassium, phosphorus
Most development and construction work means uprooting and moving around soil. Urban sprawl is a growing threat to the health of our land and its productive soil resources. The soil and water conservation society says that between 1992-1997 16 million acres of land were converted to development land (Benson, 1999). My hypothesis for this report is that the soil that has been disturbed from construction sites will have a lower pH, lower nitrogen levels, no presence of phosphorus, and low potassium levels. I came up with this hypothesis to see if exposed soil would affect the pH, therefore sending a chain reaction of other minerals in the soil to be depleted necessary for plant and turf growth. Soil pH provides clues about soil properties and can easily be identified. The normal pH of soil for turf grasses, flowers, and shrubs measures around 6.1-6.9. Usually if pH rises above the 6.5 minerals such as phosphorus will become less available. The pH of soil tends to lower when rainwater leaches away at basic ions (calcium, magnesium, potassium, and sodium), and when there is a formation of strong organic and inorganic acids. (SUNY, 2000) Nitrogen is the mineral which is most important in the productivity of plant life, testing for deficiency of nitrogen can be important if one wants to save a garden, or even a farm. Most of the time when land development is being conducted nitrogen is depleted, and salinization can occur. Phosphorus is important to soil for strong roots and resistance to disease; however, when the pH of soil becomes too high the phosphorus can become trapped causing high phosphorus levels (Whitney, 1998). The last mineral that I tested for, potassium is important for the plants ability to create sugar. Potassium can also become trapped when there are extremes in the variations of soil pH.
Materials and Methods:
pH indicator solution
Nitrogen extracting solution
Phosphorus extracting solution
Phosphorus indicator solution
Phosphorus test tablets
Potassium Indicator tablets
Potassium test solution
Test Tube, calibrated 1-8ml (4)
Test tube brush
Measuring spoons (2), .25 g and .5g
Nitrogen, phosphorus, and potassium color charts
I went to four different construction sites all on the East Side of town. I took a fifth sample from Juneau Park as a control in order to compare the undisturbed soil with the land development soil. Three of the constructions sites were located on the 18 and 1900 blocks of north Commerce St. An additional sample was taken from the 1800 block of north Palmer St. Site 1 is on the east side of the 1800 block of Commerce St, Site 2 is located on the east side of the 1900 block of Commerce St, Site 3 is located on the west side of 1800 of Commerce St, and Site 4 is located on the east side of the 1800 block of Palmer St. To take the soil samples I obtained a LaMotte soil test kit that was available in class. There were four different tests that I performed for each site and I followed the directions provided in the soil test kit.
The first test I performed is the pH test:
1) Fill test tube to line 4 with pH indicator solution, squeeze bottle gently to control the amount dispensed.
2) Use .5 g spoon to add three dippers of soil sample
3) Cap and shake for one minute
4) Allow tube to stand for ten minutes to let soil settle
5) Match color reaction with pH color chart. Record results as pH.
1) Fill test tube to line 6 with Phosphorus extracting solution
2) Use .5 g spoon to add three dippers of soil sample
3) Cap and shake for 1 minute
4) Remove cap and allow soil to settle until the liquid is clear and above the solid
5) Use one pipette to transfer clear liquid and to a second clean test tube. Release bulb slowly to draw clear liquid into pipette. Do not pull up soil. Fill second tube to line 3.
6) Add 6 drops of Phosphorus indicator solution to soil extract in second tube.
7) Cap and shake to mix
8) Add phosphorus test tablet
9) Cap and shake to dissolve tablet a blue color will develop, match test color with phosphorus color chart. The colors on the chart range from light blue, which stands for trace to dark blue, which stands for high amounts of phosphorus.
1) Fill test tube to line 7 with Nitrogen extracting solution
2) Use .5g spoon to add two dippers of soil sample
3) Cap and gently shake for 1 minute, remove and allow soil to settle
4) Use a clean pipette to transfer clear liquid to second test tube. Release bulb slowly to draw clear liquid into pipette. Fill second test tube to line 3 with liquid.
5) Use .25g spoon to add two dippers of nitrogen indicator powder to soil extract in second tube.
6) Cap and gently shake. Wait 5 minutes for pick color to develop above the powder.
7) Match color with nitrogen color chart. The colors ranged from a very light pink, meaning trace to a very dark pink meaning high levels of nitrogen.
1) Fill test tube to line 7 with potassium extracting solution
2) Use .5 g spoon to add dippers of soil sample to test tube
3) Cap and shake for 1 minute
4) Remove cap and allow to soil to settle
5) Use a clean pipette to transfer the liquid to another clean test tube. Fill the second test tube to line 5.
6) Add one potassium indicator tablet to soil extract in second tube.
7) Cap and shake to dissolve tablet, a purplish color will appear.
8) Add potassium test solution, two drops at a time, and keep count. Swirl test tube after each addition to mix contents. Stop adding drops when color changes from purple to blue.
9) Use potassium end point color chart, keep an accurate count of the number of drops added, this will be used to determine the level of potassium.
10) 0-8…Very high, 10…high, 12…medium high, 14…. Medium, 16…. medium low, 18…low, and 20 or more drops is very low.
The pH for all five sites where each an 8 on a scale of 4-8.
The Phosphorus test uses colors in order to find out how high the levels were according to the color chart. I used numbers in order to better explain my results, 1-trace, 2-light blue (low), 3-medium light blue (medium), 4- dark blue (high). In four out of the five samples the phosphorus levels were at the highest level that the LaMotte soil test kit can test for.
The nitrogen test was similar to the phosphorus test only the color was pink. I used numbers in order to make a chart, 1-light pink (trace), 2-pink (low), 3-dark pink (medium), and 4- darkest pink (high). Looking at the chart, I was only able to find trace amounts of nitrogen in two of my five samples.
The last test done was the potassium test, which came up with the most variable results. It was the control site that contained the most potassium because during the testing, it had the most sensitivity to the potassium test solution. The sites that tested for more drops of indicator had the smaller amounts of potassium.
The results for this experiment did not support my hypothesis. I figured because the soil that I was working with was exposed to the air and elements for two months or longer, that the mineral levels would drop because nothing was growing there. The only part of the hypothesis that was supported was the low presence of nitrogen in the soil. As I explained in the introduction section if there is a very high or very low level of pH the amount of potassium in soil can be high. The pH of the soil was 8, therefore this could account for why not all of the soils had a high potassium level. My soil may also have been siltier and clay like form than I actually thought they were and could have accounted for why the potassium was high. When you have this type of soil, potassium is harder to leach (Schulte, 2000). What I did find out is that when the pH of the soil is greater than 7, phosphorus is more abundant, which might account for some of the high levels of phosphorus (Busman, 1998). The pH of my soil samples was all the same; I cannot explain why this happened. It could have been due to the fact that I had picked up samples that were all within less than ˝ mile radius of one another. Many other factors could include that the soil had been exposed to the air long before I started my research, it could include there was not enough rain to lower the pH (acid rain), or less chemical run off from the construction sites than I thought there would be.
Benson, J. 1999, Soil and Water Conservation Society. The State of the Land. Conservation Voices, April-May; 1982 and 1997 Natural Resource Inventories, NCRS, USDA.
SUNY College of Environmental Science and Forestry, 1999. Soil pH: What it Means. http://www.esf.edu/pubprog/brochure/soilph.soilph.htm
Busman, L., 1998. The Nature of Phosphorus in Soils. Phosphorus in the agricultural environment. http://www.extension.umn.edu/distribution/cropsystems/DC6795.html
Whitney, D A., 1988. Phosphorus Facts: Soil, Plant, and Fertilizer. Kansas State University Publications. Cooperative Extension Service.
Schulte, E.E., (2000) Understanding Plant Nutrients: Soil and applied potassium. Cooperative Extension Publications, University of Wisconsin-Extension. http://www.uwex.edu/ces/pubs/pdf/A2521.PDF.