Vegetation and The Differences in Soil Composition: Is This a Good Method of Prediction
Ecology November 2, 1998
Soil conditions differ between southeastern and central Wisconsin as does the vegetation found there. In Waukesha county located in the southeastern portion of the state, early vegetation maps show that southern mesic forest with sugar maples, basswoods and elms predominate while in Adams county in the central part of the state, prairie grasses, jack pines and scrub oaks are found (See Figure 1). Such differences in forest composition may be attributed to soil makeup and moisture content. Since the vegetation in central Wisconsin can survive on very little moisture held in the soil, it is conceivable to say that the plants that thrive there have either deep root structures or other adaptive mechanisms that allow them to grow under those conditions. In southeastern Wisconsin, different species of deciduous trees thrive because more moisture is held in the upper layers of the soil which allows for more productivity and diversity (Hole, 1976).
Agriculture in those areas also differ because of the composition of the soil. In the central portion of the state, irrigation and fertilization is needed whereas in the southern part, drainage is most often relied upon. Because of the sandy makeup of the soil in Adams county, farmers tend to grow legumes like clover and soy beans and root crops like potatoes. Fertilizer is applied due to the leaching that takes place due to the presence of so much sand in the soil. As the water drains through the soil horizons, nutrients like nitrogen and potassium are carried down with it. In Waukesha county, the soil has more clay thus causing the moisture to remain longer in the upper horizons.
Since most of the land in southeastern Wisconsin is urban, farmers miss out on this soilís ability to produce crops. Although this area is not without its problems, the soil there does not have to be fertilized as much as the soil in the central part of the state since leaching is not as prevalent. Because of the nonporous nature of the clay soil in Waukesha county, levels of nitrogen and potassium should be higher than those in the central part of the state (Hole, 1976).
Understanding and assessing the quality of soil can lead to the use of standards which protect it for future generations. When a sandy soil like the ones found in central Wisconsin are fertilized, the natural buffering system used to balance the pH is affected and may be exhausted as the soil becomes more acidic. When this happens, it is hard to regain the use of the soil for purposes of agriculture. Learning to gauge the natural mechanisms and assess how long they may be affective has become the basis for a research project in Europe. It is the hope of researchers that by understanding the natural systems used by the ecosystem and how human interaction has either helper or harmed the soil can lead to standards which would improve the quality now and for generations to come (Eijsackers, 1998). Based on the differences in soil composition and vegetation found in the central and southeastern parts of the state, the sandy soil in central Wisconsin will have lower levels of nitrogen, potassium and moisture which is more conducive to the growth of oak scrubs and pines than the clay like soil in southeastern Wisconsin which can support a wider variety of deciduous trees.
Two different locations along with eight sites per location were used in this study. The first location is found in Muskego, Wisconsin in Waukesha county. The second site is located in the town of Preston in Adams county. Eight different sites selected on each location was done so by closing eyes and throwing a plastic plate with an arrow on it after turning around. Once the plate was tossed, a die was rolled to determine how many extra meters away from plate in the direction of the arrow were walked off before the tests were conducted. A measuring tape was used to mark off the distance from the plate to the site. Tests taken using the soil from the sites include a soil profile using a small soil corer, pH, nitrogen and potassium levels using the LaMott soil kit, moisture content using a 58cm long moisture probe. Using the same corer as above, another sample was taken and used to determine the dry mass of the soil. The soil was put through a series of sieves, sizes 60, 100 and 200, and all were weighed using an OHAUS 310 gram Dial A Balance after it was dried under artificial lighting. All samples were stored in zip lock bags placed in a brown paper bag for transport. The soil used for the other tests was also placed into zip lock bags until needed. The profile and moisture measurements were done at the site while the pH, nitrogen and potassium tests were conducted after all of the soil at one location was collected. Nitrogen and pH tests were completed for all of the samples while five sites were used for the potassium test.
Once a site was randomly selected, the soil profile was conducted. That same soil was placed into a zip lock bag and used for the dry mass determination later. Another sample was obtained using the corer, placed in another bag, and used for the other tests after the eight sites were completed. The moisture probe was used next and the mean of the measurements used for statistical analysis. When this was completed, the process began again by returning to the starting point and repeating the motions. Tests were completed with the exception of the dry mass totals for location one on Thursday October 15, 1998. A light rain fell in the morning of the experiment and the rest of the day was cloudy and cool. The tests were conducted on the second location on Saturday October 17, 1998. A light rain also fell the morning of and the rest of the day remained cool and cloudy. All of the samples were collected in the morning one after the other and the tests were completed by that afternoon except for the dry mass tests. Those were completed on Wednesday October 21, 1998. The soil from each site was placed under lights and left to dry for two hours. The total amount of soil was placed on the balance and the measurement taken before being put through the sieves. After shaking for two minutes, the soil in each of the sieves was weighed and recorded.
Differences in the soil profile were measured in centimeters using a 12 inch ruler and recorded immediately. Also recorded was any noticeable color differences, changes in density or particle size and the appearance of rocks or pebbles.
The LaMott soil kit was used to determine the pH, nitrogen and potassium levels. For each of these tests, the directions that came with the kit were followed as was the color keys for interpreting the results. The indicator used for determining nitrogen levels was different shades of pink where light pink indicated trace levels and dark pink indicated high levels. The potassium levels were determined by a titration with indicator solution and the number of drops added corresponded to the level present. This is a measure of drops and the level it corresponds to: 0-8 drops = high levels, 10 drops = high levels, 12 drops = medium high, 14 drops = medium levels, 16 drops = medium low levels, 18 drops = low levels and 20 + drops = very low or trace levels of potassium. pH was determined by matching the color of the test tube to the corresponding color on the chart once the test was completed.
For the dry mass test, an OHAUS 310 gram Dial A Balance was used along with the sieves and the mass was recorded in grams for each of the measurements. Moisture was measured on a scale from 0-10 where 0 = dry, 2-4 = average dry, 4-6 = average, 6-8 = average wet and 10 = wet. Because more than one level was generally taken per site, the average of the moisture levels was used for the t-tests. To evaluate the results, t-tests were conducted on the pH levels, moisture levels, potassium levels and dry mass totals.
Location One-- Muskego, WI Waukesha County Southeastern Wisconsin October 15,1998
Site One Soil Profile: Middle of the Yard- Top 18 cm was light to medium brown, had a few rocks and was very clay like. The bottom 6 cm was lighter in color with more pebbles and rocks in it. It contained lots of clay especially near the bottom of the profile.
Site Two Soil Profile: Elm Tree- The top 8.5 cm was medium brown in color with very little clay. The next 4 cm was lighter in color with clay streaks present. The next 8 cm was very light brown in color and contained clay. The bottom 4 cm was tan in color, had some pebbles in it and was almost all clay.
Site Three Soil Profile: Ash Tree- The top 5 cm was a loose brown soil with the next 7 cm containing more clay and was more medium brown in color. The next 7 cm was light brown and contained clay and rocks. The bottom 4 cm was tan in color, very dense and contained clay.
Site Four Soil Profile: Between Two Different Ash Trees- Very hard to get samples on this site- The top 5 cm was light brown in color and was very clay-like. The bottom 9 cm was tan in color and contained dense clay. Both layers were very dense at this site.
Site Five Soil Profile: Maple Tree- This area was very rocky and hard to obtain a sample from. The top 5 cm was brown in color and not very dense. The next 5 cm was light brown in color, had a few pebbles and was very dense. The bottom 4 cm was tan in color and was very dense and rocky.
Site Six Soil Profile: Near Shed in Open Grassy Area- The top 7 cm was dark brown in color and not very dense. The next 9 cm was medium brown in color and had clay streaks running through it and the next 5 cm had more clay in it but was similar in color. The bottom 3 cm was more tan in color and contained more clay than the other layers and was very dense.
Site Seven Soil Profile: Burn Barrel- This area was very rocky and hard to get a good profile from. The top 17 cm was light brown in color and very dense because it contained lots of clay. The bottom two 2 cm was tan in color and contained more clay and pebbles than the other layer did.
Site Eight Soil Profile: Small Blue Spruce- The top 5 cm consisted of a loose medium brown soil with not a lot of clay present. The next 4 cm had more clay than the top but it was the same color. The following 12 cm was lighter brown and contained more clay than the upper layers did. The bottom 4 cm was very dense and rocky. It was tan in color and had more clay than the other layers had.
Location Two-- Town of Preston Adams County in Central Wisconsin October 17, 1998
Site One Soil Profile: Conifer Area- The top 8 cm was a brown, fine grainy soil. The next 8 cm was light brown and fine and grainy and the bottom 4 cm was sand.
Site Two Soil Profile: Oak Patch in the Valley- The top 6 cm was a brown, fine grainy soil and the next 3 cm began to change to a caramel color. The next 8 cm remained that caramel color like wet sand when digging on a beach but the sand was not wet and the bottom 4 cm was tan color sand.
Site Three Soil Profile: Tall Pines, Small Scrub Oaks, Not Very Heavy Cover- The top 9 cm was a fine, brown soil and the next two inches began to change to a caramel color. The bottom 9 cm was light tan colored sand.
Site Four Soil Profile: Open Area With Small Pines up to One Meter Tall With Small One Meter Oaks Growing Along Side and Moss Growing on the Ground- The top 3 cm was very dark brown soil with some texture to it. It was not all sand as before. The bottom 19 cm turned into a caramel color finely textured sandy soil.
Site Five Soil Profile: Near Driveway by Three Large pines and Smaller Ones- The top 6cm was very dark brown and textured. The next 6 cm began to turn more caramel in color and more grainy as well. The bottom 9 cm was very fine and grainy containing streaks of tan sand along with its caramel color.
Site Six Soil Profile: Big Oaks and Pines Along With Smaller Pines- The top 9 cm was a fine, light brown soil. The bottom 11 cm was caramel colored sand.
Site Seven Soil Profile: Open Area With Medium Oaks Surrounding It- The top 8 cm was very dark brown and textured soil. The bottom 9 cm began to change to light brown than caramel in color. It also turned very fine and sandy.
Site Eight Soil Profile: Edge of the Marsh- The top 8 cm was very textured and almost black in color. The bottom 8 cm was more gray in color, remained textured but had more sand in it than the top layer did.
The results of the rest of the tests are found in tables one and two. The results of the statistical analysis can be found in table three along with whether to reject or accept the Null hypothesis. The first two tables contain the data from each location separately while the third table combines the results of the t-tests.
Based on what is known about soils in Wisconsin, the central portion of the state responds quickly to seasonal change due to its sandy nature ( See Figure 2). Because of this, soil there can be tilled early for optimal spring growth. It is very sandy, excessively drained and is subject to erosion. Some other characteristics include moisture ranges from poor to excessively drained, sand composition up to 90 per cent and pH ranges from 5.1-5.9 which keeps the soil in the acidic category. The profile is highly mottled depending upon the location like near a marsh or in the forest (Hole, 1976).
In southeastern Wisconsin, the soil tends to be a yellowish to grayish brown and contains more calcium carbonate than the central part of the state because of the clay found there. Because of the clay and the natural buffering system that it has, the soil pH in Waukesha county tends to more neutral to basic, more silty and clay like and poorly drained because of the texture and pore size of the clay (Hole, 1976).
The acidic nature of the soil in central Wisconsin is caused by a combination of effects like rainfall, sand and leaching. During the early stages of acidification, the upper layers of the soil become highly acidic and as time goes by, the lower layers follow this pattern. Often clay is used to returned to the soil to a more neutral pH because it contains calcium carbonate. Other contributors to acidification are fertilizers and plant life like conifers (Bohn, 1979). Major exchangeable cations are calcium, magnesium, sodium, potassium and aluminum. These ions are easily manipulated by liming, irrigation and acidification. They are important to the health of soils especially in temperate regions like Wisconsin. Some of the ions listed are ingredients in many fertilizers added to improve the quality of the soil of a region. Too much fertilization can also have adverse effects on the ecosystems present (Bohn, 1979).
Based on the results of the experiment, the soil in central Wisconsin did fit the above profile by having a high sand concentration, acidic pH and low moisture. The soil in southeastern Wisconsin also fit the above profile. It had more texture coming from the clay found in the region. It was also more neutral in pH than in central part of the state and retained more water than the sandy soil in Adams County.
Statistical analysis revealed the Null hypothesis was rejected for the moisture test, pH, and the 60, 100 and 200 sieves dry mass weight experiments. The Null hypothesis was accepted for the potassium, total dry mass weight and the 200 + sieve dry mass experiment. These show that when the Null hypothesis is rejected, the data supports the hypothesis used in this experiment. When it is accepted, the hypothesis used in this experiment is rejected. Since some support and others reject the hypothesis used in this experiment, it is inconclusive whether the composition and nature of the soils is responsible for the differences seen in the vegetation in different parts of the state.
To correct for this next time, different tests should be conducted like phosphorous, calcium and sulfur. Adding these tests could give a better overall picture of the quality of soil found and possibly gauge whether the soils are different or not. The addition of the tests could also support the hypothesis used in this experiment. Other information that could have aided in supporting the hypothesis is to find out the nutritional requirements of the trees and other plants found in each area, whether they are compatible or whether some are a part of an early successional state that has not occurred yet. This may have shed more light on whether vegetation is a way of measuring the quality of the soil and differences between regions. Another important and overlooked aspect is the history of the regions used in this study. Did something happen to the area in the past which altered the vegetation in some way? How has the effects of urbanization affected the soil? What is the vegetation of other areas that have the same soil composition as the regions used and compare the vegetation there and the history of that area.
Other variables to consider are biological like the types of bacteria present in a region and what is their function? This can be compared to other regions to see whether there is a difference or not. When the species present are determined, their function in the natural cycles like nitrogen, sulfur, and phosphorous can be examined. When this is added to the results of the chemical analysis and the physical profile, a better evaluation of the overall quality and potential differences between regions can be ascertained. Looking at the whole instead of just portions can help to provide standards like those mentioned earlier. It is important to understand the basics about the soil so that some of the variables can be left out otherwise it would become impractical timewise to conduct a study like this (Stenberg, et al, 1998).
Bohn, H. (1979). Soil Chemistry. New York: John Wiley and Sons.
Eijsackers, H. (1998). Soil Quality Assessment in an International Perspective: Generic and Land-use Based Quality Standards. Ambio , 27, 70-77.
Hole, F. (1976). Soils of Wisconsin. Madison: University of Wisconsin Press.
Stenberg, B. et al. (1998). Integrated Evaluation of Variation in Biological, Chemical and Physical Soil Properties. Ambio, 27, 9-15.