Comparisons of pH and Phosphorus Levels in Pine and Deciduous Soils

Wendy Zoltak



Abstract: Five soil samples were taken from two different areas, pine and deciduous forests. The soils were then tested for their pH and P levels. The hypothesis is that the pH level of soil is going to be lower in a pine forest verses other areas, and the P level will be highest in the pine soil than in the other soils tested. The results showed that the pH levels of soil from a pine forest were acidic, but the phosphorous levels were zero in the pine soils.

Keywords: pH levels, Phosphorus levels, pine and deciduous soils, significant difference

Introduction: Pine needles contain tannins that are highly acidic. When the needles fall off the trees, they start to decompose into the soil. The soil should therefore have a low acidity level. For example, the pine soil may have a pH of 4.5 verses different types of soil having a pH of 6.6.

According to an experiment performed by Stefan Scheu and Matthias Schaefer in 1998, " soil microorganisms were primarily limited by phosphorous". I am hypothesizing that the P level will be high in a pine soil because of the acidity therefore only allowing for microorganisms that can live in high acidic soils in special conditions. Phosphorus is one of the essential nutrients required for growth (Lory,1999). If P levels were low than I would expect to see low vegetation and animal species. In both areas I saw plenty of vegetation growth. I am inferring that there will only be diverse species of microorganisms that can live in the acidic soil, therefore leading to the high P levels.

Methods: Five soil samples were collected from a pine forest area in Greenfield Park located on 124th and Lincoln Avenue. Five soil samples were collected from a deciduous forest from the same park. The samples were collected on October 24,th 2000 at 9:00am. The temperature was about 12.1 C΄ and it was sunny. Ten sterile plastic bags were used to hold the soil samples, and a sterile scoop was used to dig about 2.5centimeters into the ground to collect the soil.

The soils had to be randomly selected in order for the experiment to be true. A yellow disk was used to toss in the air to determine where to start digging. The initial spot was selected by randomly walking twelve meters into each forest going west for the pine forest and walking east for the deciduous forest. Once the soils were all collected, the samples were taken to be tested using a soil test kit.

The pH was first tested. Sterile test tubes provided in the kit had quantitative lines marked on them. A tube was filled to the four-mark line with pH indicator. To fill three scoops of soil to mix with the test tube containing the indicator, a .5g scoop was used. The tube was capped and then shaken for one minute. The sample was set down and was read after ten minutes by using the pH chart provided in the kit. This step was repeated for the rest of the samples.

To test the soil for phosphorous, several steps were taken. First, a sterile test tube was filled with P indicator to line six. Next, three scoops of soil were added. The solution was shaken for one minute, and then set down and left to let the sediment drop to the bottom. Once the soil sediment was on the bottom of the tube and the liquid was clear, the next step could be completed. Using a sterile dropper, the soil liquid was sucked up and added to another sterile tube to the three-mark line. Then six drops of the P extract was added to the new tube and mixed together. Next, a P tablet was added to the tube and shaken. The tube was then set down to let the pill dissolve. Once the whole pill was disintegrated into the liquid, the P chart provided by the soil kit was used to determine the P level in the soil. This procedure was repeated for the remaining soil samples.


Results: As you can see from the charts above and the t-test of .03, there is a significant difference between the pH levels of pine and deciduous forest’s soils. For example, the pHs for the non-pine soil was all 8, which is basic and just above neutral. The pine pH’s ranged from 5 to 8. Most of the levels tested were acidic with a few basic samples. The phosphorous results were not graphed or t-tested because there was no P found in any of the soil samples using this particular P kit.

Discussion: The pine soils were found to have a lower acidic level than a higher level. The results for the pH are significant amongst the two but I believe it is because there were not a lot of samples and because the pH for the non-pine soil was constant throughout. I was hoping for the pine pH levels to be more in the 4 and 5. There was one sample with a pH of five.

I thought it was also peculiar that the pH for the non-pine soils was all the same. I thought they would be different because they were random samples of soils with different decaying material on top of the soil. I also noticed in the area that there were a lot of Rhamnus cathartica and Rhamnus frangula species. These species are from the buckthorn family and are very invasive. They are also known to grow in low nutrient soils (WI-DNR,1999). This is another reason why I thought perhaps the deciduous soils would be more basic after I collected the samples.

If the test was done over again, I would like to take more than five samples of each area, and I would like to go to more parks in the county. I would also like to try a different pH tester to see if the accuracy of another test.

As for the P levels not appearing in any of the samples leads me to believe that there was a possible mistake in the testing procedure or that Wisconsin has very low P levels in soil. I believe both theories could be possible. I need to find more information on Wisconsin’s soils on P levels or I need to run some new tests with new soil samples.

Overall, the procedures and methods used to give significant results for the pH groupings. Pine soils are more acidic than deciduous soils and the hypothesis can be supported.


Lory. A. J., April 1st, 1999. "Agricultural Phosphorus and Water Quality" Department of Agronomy and Commercial Agriculture Program.

Scheu. S., Matthias. S., 1998: "Bottom-Up Control of the Soil Macrofauna Community in a Beechwood on Limestone: Manipulation of Food Resources". Ecology: Vol.79,No.5,pp. 1573–1585.

WI-Dept. of Natural Resources, April 30th, 1999. "Common Buckthorn, (Rhamnus cathartica)"…invasive/factsheets/buckthorns.htm