Figure 1: Soil pH
Figure 1. pH Straw vs. No Straw
Note: This graph compares the pH of the conditions of soil with straw and soil without straw. The data shown in the graph is the average (mean) and standard deviations with respect to the entire class. “X” on the graph represents the average pH for each condition. The unpaired t-test, assuming unequal variance was found and came out to p = 0.398. This value is greater than the p = 0.05 value, meaning that the data is not statistically significant. After finding out our mathematical values we can then conclude that there is no statistical difference between the pH of soil with straw and soil without straw.
Method
Before data could be mathematically calculated the soil had to be tested in the lab. The soil gathered from the garden was put into tubes with deionized water and was then mixed with a vortex to combine. The soil was then incubated at room temperature for 30 minutes before using a pH probe to determine the pH values.
Evidence
The pH of condition one, soil with straw, had an average of 8.13125 compared to the pH of condition two, soil without straw which had an average of 8.00375. While still very similar in pH, the pH of soil with straw is roughly 1.6% greater than the pH of soil without straw. The standard deviation of soil with straw was 0.2574844 compared to the soil without straw which was 0.3233723. This means that the standard deviation of the soil with straw is lower than the standard deviation of soil without straw, therefore there was less variability in the pH values from the soil with straw data. The p-value from the t-test performed was p = 0.398 which is greater than the threshold value p = 0.05 meaning there is no statistical significance. Therefore, there is no statistically significant difference between the two pH conditions.
Conclusion
Condition 1 (soil with straw) and condition 2 (soil without straw) both provide unique pH values when it was originally thought that the values would be different from each other. After performing the t-test to compare the two values from the standard deviation, it was instead proven that there was no significant difference between the pH values. Thus, despite initial confidence, the p values found show that there is no significant difference, and we cannot be confident with these results.
Explanation
There are many factors that go into changing the pH of soil. Several of these factors include the rock from which the soil was formed and the weathering processes that go into it like climate, vegetation, topography, and time (Queensland). The pH scale ranges from 0 to 14 with anything under 7 being acidic, over 7 being alkaline or basic, and 7 being neutral. The pHs found in this experiment were roughly 8, making them both basic pHs of soil. These pH values are unique to each other when it was originally thought they would be more different as one soil condition was covered with straw and the other was not. When obtaining the soil samples from Erie Street Community Garden, the soil underneath the straw was dark colored, moist, and soft but the soil underneath the straw was lighter, dry, and rocky. With these observations, it was hypothesized that the pHs would be different. It can then be concluded that the decomposition of the straw into the soil had no effect on the soil pH and therefore it made the pH values the same. Since they have the same pH, it cannot be proven that straw can affect soil differently or not.