Figure 2: Moisture Content
Figure 2. Moisture Content Straw vs. No Straw
Note: Percent moisture for the two conditions, straw and no straw, are being compared here. Class data was taken, and the mean data are graphed with standard deviations. We collected the data by drying out the soil samples to figure out how much mass in the sample was due to moisture, then expressing this value as a percentage. The mean for straw is 24.87% and no straw was 17.37%, indicated by x’s on each box and whisker plot. The unpaired t-test assuming unequal variance was taken and yielded a value of p = 0.065, which is greater than the 0.05 threshold, thus the data is not statistically significant. There is no significant difference between the moisture content of straw and no straw soil.
Method
To figure out the moisture content of the samples from our two conditions, we started by weighing a sample of soil then drying that sample for one week in a 100 degree C oven. After a week, we weighed the dried soil and computed a percent moisture content. This is done with the equation (mass before – mass after)/mass after x 100. The reason this equation works is because the mass before minus mass after represents just the water from the sample, then you divide by the mass of just the soil, because the mass after is just soil with all the water dried out. Effectively, the equation describes (water/soil mass) x 100%.
Evidence
The straw moisture content had an average of 24.9% while the no straw condition had a 17.4% moisture content. This means that the soil covered in straw had approximately 40% more moisture than soil with no straw. The standard deviation of our straw condition was lower (6.15) than standard deviation of no straw (8.54), which means that there was less variability in the moisture values from the straw data. The p-value from our t-test was 0.065, which does not have statistical significance because it is greater than p=0.05 which is the threshold for statistical significance. There is not a statistically significant difference between the two conditions.
Conclusion
Condition 1 and condition 2 (straw and no straw areas) have unique moisture contents upon first look at the data, and initially, we were quite confident that the two conditions provide different moisture contents, but when we performed a t-test to compare the standard deviations, there was no significant difference between the moisture contents. In conclusion, there are unique moisture contents, but we cannot be confident that these are correct because there is no statistically significant difference.
Explanation
Different types of mulch affect the moisture content and water retention of soil. In a study conducted at the Japan International Research Center for Agricultural Sciences in 2018, researchers evaluated the changes in moisture content when different fertilizers or mulch were applied. The mesh mulch had the highest water retention while the unaffected control had the lowest water retention. The other types of mulches, including putting organic material on the soil (which presumably has similar properties to using straw mulch), also had higher moisture contents than the control, which indicates that any sort of intervention will improve water retention (Raysid et al). However, our data does not support this conclusion because there was no statistically significant difference between the moisture contents of each condition. The benefit to making sure soil is properly irrigated and retaining as much moisture as possible is improving plant health. According to a study done by researchers in Poland, there are many adverse effects on plants due to drought. Molecular and physiological changes in the plants lead to smaller organs being grown, and this reduced biomass decreases the overall productivity of the plants (Galezewski et al). Daryanto et al. conducted research on maize and wheat, and 40% less water led to 39% and 20% lower yields for these two crops. The conclusion that can be drawn from this research is that adding mulch to soil would most likely benefit the plants being grown in the Erie Street Community Garden, but the current mulch system of having straw on some areas and no straw on others is not causing a significant difference, so it is not as effective as other potential mulching methods. This could be due to not having enough straw, not enough moisture, the straw wasn’t sitting and decomposing long enough, or other extenuating circumstances.