Problem
How does the porosity of soil affect the permeability and what soil type has the best advantage from its' porosity and permeability?
Hypothesis
The pebbles will be more permeable than sand because they are more porous and the amount of space between pebbles allows for the transmission of water to occur easily.
Parts of the Experiment
Independent Variables: type of soil
Dependent Variables: permeability of soil
Controlled Variables: temperature, amount of water, jar size
Experimental Group: pebble and sand groups
Dependent Variables: permeability of soil
Controlled Variables: temperature, amount of water, jar size
Experimental Group: pebble and sand groups
Materials
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Pre-Lab Questions
1. Define the following:
a. Porosity: a measure of how much of a rock is open space
b. Permeability: the rate of flow of a liquid or gas through a porous material
c. Water holding capacity: the specific ability of a particular type of soil to hold water against the force of gravity
d. Solution: a homogeneous mixture of two or more substances in which the molecules or atoms of the substances are completely dispersed
e. Suspension: a dispersion of fine solid or liquid particles in a fluid
2. What industries would find it important to know the structure of the soil?
Agriculture, construction, and mineral extracting industries, such as mining, would find it important to know the structure of the soil.
3. Using what you know about North Carolina now, would large scale use of septic tanks work well?
No it would not because water would get stuck in clay because clay has a low permeability and North Carolina has a lot of clay.
4. Use the soil triangle to decide what type of soil the following are.
a. 10% Clay, 60% Sand, and 30% Silt
Sandy loam
b. 60% Clay, 20% Sand, and 20% Silt
Clay
c. 20% Clay, 20% Sand, and 60% Silt
Silt loam
d. 20% Clay, 40% Sand, and 40% Silt
Loam
a. Porosity: a measure of how much of a rock is open space
b. Permeability: the rate of flow of a liquid or gas through a porous material
c. Water holding capacity: the specific ability of a particular type of soil to hold water against the force of gravity
d. Solution: a homogeneous mixture of two or more substances in which the molecules or atoms of the substances are completely dispersed
e. Suspension: a dispersion of fine solid or liquid particles in a fluid
2. What industries would find it important to know the structure of the soil?
Agriculture, construction, and mineral extracting industries, such as mining, would find it important to know the structure of the soil.
3. Using what you know about North Carolina now, would large scale use of septic tanks work well?
No it would not because water would get stuck in clay because clay has a low permeability and North Carolina has a lot of clay.
4. Use the soil triangle to decide what type of soil the following are.
a. 10% Clay, 60% Sand, and 30% Silt
Sandy loam
b. 60% Clay, 20% Sand, and 20% Silt
Clay
c. 20% Clay, 20% Sand, and 60% Silt
Silt loam
d. 20% Clay, 40% Sand, and 40% Silt
Loam
Procedure
Determining Soil Texture
1. Using the soil assigned to your group, follow the directions to classify the type of soil you have. Then, record the results in the table below, including the percentages of each type of soil.
1. Using the soil assigned to your group, follow the directions to classify the type of soil you have. Then, record the results in the table below, including the percentages of each type of soil.
Hydrologic Soil Analysis
- Using a mortar and pestle, crush enough soil to fill about 1/3 of the jar provided.
- Remove any pieces of rock larger than about 2mm (between 1/16” & 1/8”).
- Put the soil into the jar and fill it with water, leaving about an inch of space at the top, and put the lid on the jar.
- Shake the jar for a couple minutes.
- Allow the contents of the jar to settle.
- After about a minute, put a line at the top of the sediment that settled first. This is sand.
- After a couple hours put a mark at the top of the sediment that settled next (someone from the group will have to come back later to do this). This is silt.
- After two days mark the top of the last later of sediment. This is clay (it will probably not all settle, some of it can float in there for many days.)
- Measure the total height of the sediment in the jar in cm. Measure the thickness of the sand, silt and clay layers and calculate the percentage of each. Record these measurements in the table below.
- Make sure to include a picture of your final results.
- Use the soil triangle to determine the type of soil you have. Compare this to what you determined by feel.
Data Table 1: Soil Composition
Determination of Permeability
1. Suspend the soil column about 1 inch above a beaker.
2. Put 100mL of water into a graduated. Designate one member as the timekeeper and one as the recorder. When everyone is ready, pour the water onto the wet sand. The timer should time how long it takes until the first drop of water comes out of the bottom of the column. Set up a data table to record this information. Watch the column until there is not more water standing above the soil and no more dripping through the column. Record this time as well.
3. Repeat with the pebbles column.
2. Put 100mL of water into a graduated. Designate one member as the timekeeper and one as the recorder. When everyone is ready, pour the water onto the wet sand. The timer should time how long it takes until the first drop of water comes out of the bottom of the column. Set up a data table to record this information. Watch the column until there is not more water standing above the soil and no more dripping through the column. Record this time as well.
3. Repeat with the pebbles column.
Data Table 2
Lab Questions
1. Considering all the samples analyzed by your class in the first three parts, do you find any relationship between texture and composition?
There is a relationship between texture and composition because of the permeability and porosity of the samples. Samples that stayed together when combined with water were composed more of clay. Other samples fell apart or became mushy when water was added, showing that they were primarily composed of sand.
2. Compare and contrast the texture analyzed by feel and hydrologically. How do your results compare? Explain any discrepancies.
After feeling the sample, we decided our soil was sandy clay loam based on the flow chart. The sample was gritty and could be stretched into the shape of a ribbon. After testing it hydrologically, we found the sample was loamy sand. There is not much difference between the two results which lie on each side of sandy loam on the soil triangle. Loamy sand is not able to be stretched into a ribbon according to the flow chart which is the largest difference between the results.
3. Do you believe one type of soil composition test (by feel or with water) is more reliable than the other? Explain your answer.
I believe the hydologic soil composition test is more reliable because it compares different layers of the soil sample and separates the components with the properties of the water. This shows what components make up the soil sample and can also provide a specific number or percentage on the amount of each component. The test by feel can easily confuse two soil samples since some properties are difficult to judge by feel.
4. How might the composition of soil affect the growth of plants? Think about wet and dry conditions.
Plants need specific soils to aid their growth, mostly in the placement of their roots. Sand is not ideal for many plants because its' properties limit the amount of water it can hold. Clay is not ideal for many plants either because it can hold a lot of water and could lead to excess water for the plants which is detrimental. It also limits the movement of roots. Silt has properties of both clay and sand which makes it ideal, however other combinations may be needed to meet the individual needs of the specific plant.
5. What characteristic of soil is most important in determining water holding capacity?
The size of particles is the most important because it determines how much water can infiltrate the sample. Clay has smaller particle size making it able to carry more water. Sand has a larger particle size, allowing it to hold less water.
6. Imagine a sloping field of very sandy soil and a sloping field of soil with a very high clay content, each with an identical drainage ditch at the bottom. In a prolonged heavy downpour, do you think one ditch will be more likely to flood then the other? Why?
I think the drainage ditch in the sandy soil area would flood quicker because sand is not able to hold as much water as clay is. Clay has a higher water holding capacity so it would take longer to flood.
7. If you have two fields of crops, one in which the soil was mostly sand and the other mostly clay, which would you have to water most often and why?
You would have to water the sand field most often because its' porosity allows water to quickly flow through it. Clay can hold water for a long time and wouldn't need to be watered as often.
8. Use the information you have collected about the local soil samples and suggest how this would affect agriculture and building in the area.
Clay would be ideal for building on top of because it is more compact and would be safer than building on top of sand. It would not be wise for clay to be used in mass agriculture use because the roots would not be able to grow since the clay is so tight and packed together. The porosity and permeability of sand would be better for agriculture, especially if mixed with clay or silt to obtain the useful properties of each soil type. Farmers would want a mixture that holds a good amount of water without being waterlogged and also has space for roots to grow.
There is a relationship between texture and composition because of the permeability and porosity of the samples. Samples that stayed together when combined with water were composed more of clay. Other samples fell apart or became mushy when water was added, showing that they were primarily composed of sand.
2. Compare and contrast the texture analyzed by feel and hydrologically. How do your results compare? Explain any discrepancies.
After feeling the sample, we decided our soil was sandy clay loam based on the flow chart. The sample was gritty and could be stretched into the shape of a ribbon. After testing it hydrologically, we found the sample was loamy sand. There is not much difference between the two results which lie on each side of sandy loam on the soil triangle. Loamy sand is not able to be stretched into a ribbon according to the flow chart which is the largest difference between the results.
3. Do you believe one type of soil composition test (by feel or with water) is more reliable than the other? Explain your answer.
I believe the hydologic soil composition test is more reliable because it compares different layers of the soil sample and separates the components with the properties of the water. This shows what components make up the soil sample and can also provide a specific number or percentage on the amount of each component. The test by feel can easily confuse two soil samples since some properties are difficult to judge by feel.
4. How might the composition of soil affect the growth of plants? Think about wet and dry conditions.
Plants need specific soils to aid their growth, mostly in the placement of their roots. Sand is not ideal for many plants because its' properties limit the amount of water it can hold. Clay is not ideal for many plants either because it can hold a lot of water and could lead to excess water for the plants which is detrimental. It also limits the movement of roots. Silt has properties of both clay and sand which makes it ideal, however other combinations may be needed to meet the individual needs of the specific plant.
5. What characteristic of soil is most important in determining water holding capacity?
The size of particles is the most important because it determines how much water can infiltrate the sample. Clay has smaller particle size making it able to carry more water. Sand has a larger particle size, allowing it to hold less water.
6. Imagine a sloping field of very sandy soil and a sloping field of soil with a very high clay content, each with an identical drainage ditch at the bottom. In a prolonged heavy downpour, do you think one ditch will be more likely to flood then the other? Why?
I think the drainage ditch in the sandy soil area would flood quicker because sand is not able to hold as much water as clay is. Clay has a higher water holding capacity so it would take longer to flood.
7. If you have two fields of crops, one in which the soil was mostly sand and the other mostly clay, which would you have to water most often and why?
You would have to water the sand field most often because its' porosity allows water to quickly flow through it. Clay can hold water for a long time and wouldn't need to be watered as often.
8. Use the information you have collected about the local soil samples and suggest how this would affect agriculture and building in the area.
Clay would be ideal for building on top of because it is more compact and would be safer than building on top of sand. It would not be wise for clay to be used in mass agriculture use because the roots would not be able to grow since the clay is so tight and packed together. The porosity and permeability of sand would be better for agriculture, especially if mixed with clay or silt to obtain the useful properties of each soil type. Farmers would want a mixture that holds a good amount of water without being waterlogged and also has space for roots to grow.
General Analysis & Conclusions
Evaluation of Hypothesis: My hypothesis proved to be correct because the pebbles had a higher permeability than sand. The sand did not allow any water to pass through it while the pebbles drained water almost instantaneously.
Accuracy of Results: At first, my group didn't add enough water to our soil sample so we had to add more water before we were able to determine the composition of the substance using the "Soil Texture by Feel Flow Chart". Also, none of the sand samples were able to have water pass through the bottle. We waited an additional two minutes for any water flow. Perhaps the results should have been measured over a longer period of time. There may have been an error between the groups in when the water actually began to flow because it is difficult to judge when it happens so fast.
Application: Soil analysis is an important tool for many reasons and testing soil can help in the choosing of the most efficient soil for the specific use. Wayne Cahilly has a method he uses to determine soil composition and quality which could be used in many homes in order to improve gardening. On a larger scale, Cahilly's method could be implemented into large agricultural farms. The method can be practiced using common household items and is a time saving alternative to sending a soil sample to the lab. By using a jar, a cookie tray, soap, and the other necessary items for the test, soil composition can be determined and gardeners will be aware whether they should be adding more clay, sand, or silt to their soil.
Citation: Cahilly, Wayne. "How Is Your Soil Texture?" Fine Gardening. N.p., n.d. Web. 19 Apr. 2013.
http://www.finegardening.com/how-to/articles/hows-your-soil-texture.aspx
Accuracy of Results: At first, my group didn't add enough water to our soil sample so we had to add more water before we were able to determine the composition of the substance using the "Soil Texture by Feel Flow Chart". Also, none of the sand samples were able to have water pass through the bottle. We waited an additional two minutes for any water flow. Perhaps the results should have been measured over a longer period of time. There may have been an error between the groups in when the water actually began to flow because it is difficult to judge when it happens so fast.
Application: Soil analysis is an important tool for many reasons and testing soil can help in the choosing of the most efficient soil for the specific use. Wayne Cahilly has a method he uses to determine soil composition and quality which could be used in many homes in order to improve gardening. On a larger scale, Cahilly's method could be implemented into large agricultural farms. The method can be practiced using common household items and is a time saving alternative to sending a soil sample to the lab. By using a jar, a cookie tray, soap, and the other necessary items for the test, soil composition can be determined and gardeners will be aware whether they should be adding more clay, sand, or silt to their soil.
Citation: Cahilly, Wayne. "How Is Your Soil Texture?" Fine Gardening. N.p., n.d. Web. 19 Apr. 2013.
http://www.finegardening.com/how-to/articles/hows-your-soil-texture.aspx