The Effect Vegetative and Non-Vegetative Areas have on Moisture Levels in the Soil




Tracy Hedrick



Fall 2009



            I tested soil moisture level among different areas of the stream in Madison Park, Wauwatosa, WI.  I selected an area with a small stream to see if there were any differences on a smaller scale.  Using the soil moisture meter I measured the amount of moisture in the soil.  After collecting and interpreting the data, I was able to tell which areas had more moisture.  The areas of thick vegetation were defined as having more than 10 trees and thin vegetation consisted of less than 10 trees.  The thick vegetative areas did not have more soil moisture (mean 8.4, SD: 2.01) than thin vegetative areas (mean 8.1, SD: 2.02).  The p-value was 0.38. 

Keywords: vegetation, moisture, soil



            Gallardo, et al. (1996) states that root systems grow in areas where there is high nutrient and water availability.  Because of this, I chose to test soil moisture near a stream.  Ruiz-Sanchez, et al. (2005) stated that plant roots that grow horizontally cover more surface area.  The purpose of this experiment was to test soil moisture levels among two different areas of vegetation, thick and thin.  My hypothesis stated that areas of thick vegetation would have higher soil moisture meter levels than areas of thin vegetation (agreeing with Ruiz-Sanchez, et al. study since the thin root systems would absorb more water than thick on the surface because thick vegetative root systems would be further down into the ground).  We would be able to use this information to help learn more about the root systems and the amount of water that gets taken up from the roots. 



Materials & Methods


An area was scouted out in between Madison Park and the Fountains of Wauwatosa apartment complex, Wauwatosa, WI.  Area selected on a sunny Sunday morning, November 1, 2009 at approximately 10:00 am.  The area was haphazardly selected from the Northeast end of the stream.  Two different areas were determined by the noticeable difference in vegetation within a short distance, ten measurements were recorded per site.  Area 1 was the thick vegetation and area 2 was the thin vegetation.  Measurements were taken from the sites at 5 m apart and 5 m up from the stream.  Measurements were taken from the site using a Benchmark 100 ft fiberglass tape measure.  I first calibrated the soil moisture meter to make sure it was reading properly.  Then I stuck the probe of the LIC Soil Moisture Meter (Alverno inventory #: 20327) approximately 5 cm into the soil and recorded the results.  Originally I stuck the probe into the ground approximately 10 and 15 cm in but all of the readings were 10 because it had rained for a few days prior to the experiment.  When I used 5 cm, I started to get different results.  At each location measurements were taken 5 m apart, soil moisture levels were recorded, and classification of thick or thin vegetation of the area was noted. 



            I input my data into Excel 2007 for Windows and found the mean, standard deviation as well as using a type 1, 1 tail t-test.  After performing a type 1, 1 tailed t-test to compare the data of the different areas, the p-value of 0.38 was found.  No statistical significant difference was found in the soil moisture levels among thick and thin vegetation (p-value 0.38).  A mean of 8.4 for thick vegetation and 8.1 for thin vegetation was found for the different areas tested (Figure 1).   The standard deviation was 2.011 for thick vegetation and 2.025 for thin vegetation.  It was found that thin vegetative areas had less soil moisture than found in thick vegetative areas, but not enough to make a significant difference.


Figure 1. The soil moisture level was not significantly higher in thick vegetative areas (mean 8.4) and lower in thin vegetative areas (mean 8.1).  






As Ruiz-Sánchez, et al (2005) states, the fine root systems of my thin area may spread horizontally and cover a greater area of soil.  The thin area of my testing had a flatter landscape than the thick area did; which also allowed for a greater spread horizontally.  It is widely known that grasses have a horizontal root system as trees have more of a vertical root system.  Grasses were found more in the thin area of my study as trees were found in the thick vegetative area as described above.  The thick area was more inclined possibly due to erosion.  

A root system that is more horizontal may allow the uptake of soil moisture (especially after rainfall) than that of a vertical system since the water would have to filter down further into the soil to be taken up by the tree roots there.  Farley & Fitter, (1999) state that plants have a horizontal spread of +20cm will be able to obtain localized nutrients in the soil (ex. from leaching of tree litter after rainfall) and that this can be advantageous in comparison to vertical root system spreads.  This proved my hypothesis, and gave a clear explanation why the moisture levels would be lower in areas of thin vegetation. 

If I were to do this experiment again I would choose a testing area with a similar landscape to prevent any impact on my findings.  The fact that the landscape was pretty flat for the thin area of vegetation along with the shallow horizontal root systems of that area could have lessened the soil moisture levels as well as the sun being able to beat down on it without a lot of shade.    The area of thick vegetation included an incline allowing for water to run down into the stream easier than the flat (thin) area.  The thick vegetation also had a lot of shaded areas which would not allow the sun to penetrate through to dry the soil as effectively as non-shaded areas. 

Literature Cited

Farley, R.A., & Fitter, A.H. (1999). Temporal and spatial variation in soil resources in a deciduous

woodland. Journal of Ecology, 87(4), 688-696.  Retrieved November 5, 2009 from EBSCOhost database. 

Gallardo, M., Jackson, L.E., & Thompson, R.B. (1996).  Shoot and root physiological responses to

localized zones of soil moisture in cultivated and wild lettuce.  Plant, Cell and Environment, 19(10), 1169-1178.  Retrieved November 5, 2009 from Wiley InterScience database.

Ruiz-sánchez, M.C., Piana, V., Ortuño, M.F., Tapia, L.M., & Abrisqueta, J.M. (2005). Spatial root

distribution of apricot trees in different soil tillage practices. Plant & Soil, 272(1/2), 211-221.  Retrieved November 5, 2009 from EBSCOhost database.