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Soil Texture

Soil texture is a soil property used to describe the relative proportion of different grain sizes of mineral particles in a soil. Particles are grouped according to their size into what are called soil separates. These separates are typically named clay, silt, and sand. Soil texture classification is based on the fractions of soil separates present in a soil. The soil texture triangle is a diagram often used to figure out soil textures.

A sandy soil is one with large particles that drains quickly but holds nutrients poorly.

A clay soil is composed of extremely small particles, with a large capacity for holding water and dissolved plant nutrients. Un-amended clay soil is sticky, heavy, and hard to breathe. It tends to expand when wet and crack apart when dry.

A silt soil is one with medium-size mineral particles, larger than clay and smaller than sand. Silt adds little to the characteristics of a soil.

The term loam refers to a soil with a combination of sand, silt, and clay sized particles.

Instructions: Soil Texture

Day 1:

1. Place 20 mL of soil sample in the 100 mL graduated cylinder. (If you are using a 50 mL graduated cylinder, fill with 10 mL of soil)

2. Add water until the total volume of soil and water is 100 mL (if you are using a 50 mL grad cyl, fill to the 50 mL line)

3. Cover the top of the graduated cylinder with BOTH Parafilm AND your hand. Shake for one minute. You may have to shake the cylinder to mix the water and soil thoroughly.

4. Label your cylinder with tape (Names and class period) and set on a side counter.

Day 2:

5. The different soil materials will settle to the bottom at different rates depending upon their particle sizes: sand size > silt size > clay size.

6. Estimate the volume of the sand, silt and clay layers using the marks on the graduated cylinder. There should be at least three reasonably distinct layers in the graduated cylinder representing sand (bottom), silt (middle) and clay (top). There may also be a dark humus layer above the clay layer, or possibly floating on top of the water.

7. Using the soil texture triangle, find the spot on the diagram that corresponds to the fractions of sand, silt and clay in your soil test. Write down the name of your soil texture.

8. For example, the soil texture as determined by the triangle for a soil with 50% sand, 12.5% silt and 37.5% clay is a Sandy Clay Soil. You can now use this soil texture classification when estimating water, and fertility requirements of your soil, as well as choosing the best amendment for your soil.

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Soil Texture Data and Analysis

Record your data in your research notebook

Table 1: Data collected on our sample _________________________ showing percentages of different soil components

Soil component mL of component Percentage of component (ml of component/total ml)

Sand (at bottom) Silt (in middle) Clay (at top) Total (sum of all three ml)

Using the soil triangle below, determine what type of soil you have:

______% Sand ______%Silt ______% Clay Soil Texture ______________________________

Table 2: Class results on soil texture (fill out yours, get results from others during discussion): Sample Name % sand % silt % clay Soil Texture

Determined from Triangle

Garden Bed Lawn

Oklahoma Sample

Potting Soil

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Soil Permeability Permeability is the measure of the size and connectedness of the open spaces in a rock or soil. Generally materials of a larger particle size (and that are well-sorted) are more permeable.

Instructions: Soil Permeability

1. Fold a piece of filter paper in half. Fold in half again. Gently push corners together to form a cone. Open the cone so that it resembles a funnel and place in the mouth of a vial. Repeat until you have 4.

2. Put 10g of sand to one funnel. 10g of clay in the second funnel. 10 g of Garden Bed Soil in the third funnel. And 10 g of Lawn Soil in the fourth funnel.

3. Using the graduated cylinder. Slowly pour 10 ml tap water to each funnel. 4. Wait for 10 minutes. 5. Collect the water now settled in the container and carefully pour it back into the now-empty graduated

cylinder. Record the amount of water drained through the pot on the data table. 6. Calculate the percentage of water retained by all samples. Record this on the data table. 7. Now calculate the rate of drainage by dividing the amount of water drained in each vial by the amount of

time it took for the water to drain. Record this on the data sheet. 8. Clean-up this station. Pour the wet soil in the appropriate bucket and throw away the filter.

Soil Permeability Data and Analysis

Record your data in your research notebook

Table 3: Soil Permeability Data.

Soil Sample Starting water volume

Ending Water Volume

Time to drain

Sand

Clay

Garden Bed

Lawn

Table 4: Soil Permeability Calculations

Our Data Class Average

Soil Sample % retention Rate of

drainage % retention Rate of

drainage

Sand

Clay

Garden Bed

Lawn

Questions: 1. Compare the texture and permeability of the Garden Bed and Lawn soil. 2. Use data from the lab to explain which soil will have better drainage.

Explain why loam soil will result in the most oxygen for roots? 3. What problems could occur in the Oklahoma garden soil? Use data from the lab to explain the

problem.

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Soil Density Soils that are very dense have high strength, low porosity, and poorly support plant growth. Soils can become compacted in many ways such as overgrazing by livestock or a high amount of traffic over the soil.

Instructions: Soil Density

Materials: sand samples, clay samples, soil samples, 50-100 mL graduated cylinder, paper towels,

IMPORTANT: Samples must be DRY – you can leave a small amount of soil out to dry on a paper towel overnight or place in the drying oven.

1. Weigh out 15 g of your soil sample.

2. Pour into a dry 50-mL or 100-mL graduated cylinder. Tap gently on the table to settle the particles.

3. Determine the volume of soil in the cylinder.

4. Calculate the bulk density and record in a table like the one below.

5. Pour the sample back into the stock container. Tap out grad cylinder thoroughly but DO NOT WASH as the moisture will make it challenging for the next group.

Soil Density Data and Analysis

Record your data in your research notebook

Table 5: Soil Density Data

Our Data Class Average Data

Sample Mass Volume Density (g/mL)

Mass Volume Density (g/mL)

Sand

Clay

Garden Bed

Lawn

Questions: 1. How could soil become compacted in an urban garden setting?

2. What is one measure that could be taken to prevent and one way to remedy compacted soil in an urban

garden?

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Soil pH The acidity of soil determines the nutrient status of the soil. In general, more acidic soils (Lower pH) have a lower fertility than the more basic soils because the Hydrogen ions in acids displace the positively charged nutrient ions on the soil micelle. These nutrients can then be leached from the soil.

Instructions Soil pH

You will be using the Lamotte pH Module for Soil Macronutrients Kit. These are the directions that go with that kit. All materials should be stored in and returned to the blue kits when finished.

The figure to the right shows the procedure.

Soil pH Data and Analysis

Table 6. pH Data:

Our Data

Class Ave.

Sample pH pH

Garden Bed

Lawn

Questions:

1. Compare the acidity of the Garden Bed and Lawn soil – were they acidic, basic or neutral?

2. What does the pH tell you about the fertility of the soil?

3. How does pH influence the fertility of soil?

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Soil Nitrogen

Nitrogen is a part of every living cell. As a component of amino acids, the building blocks of proteins, nitrogen is a vital link in the world’s food supply. Nitrogen is directly involved in photosynthesis. It stimulates above ground growth and produces the rich green color characteristics of healthy plants. Nitrates, the available form of soil nitrogen, are produced through the decomposition of organic matter, the application of nitrogen fertilizers, and the fixation of atmospheric nitrogen by microorganisms in the roots of legumes. Soil nitrogen is depleted through harvesting crops, leaching by rainwater and denitrification.

Instructions for Soil Nitrogen

You will be using the Lamotte Nitrogen Module for Soil Macronutrients Kit. These are the directions that go with that kit. All materials should be stored in and returned to the blue kits when finished.

1. Fill a test tube (0755) to line 7 with *Universal Extracting Solution (5173) 2. Use 0.5 g spoon (0698) to add 4 level measures of soil. Cap and shake for one minute. NOTE: when

adding samples with high concentrations of carbonates to *Universal Extracting Solution (5173), swirl tube to mix for 30 seconds before capping to allow gases to escape.

3. Fold a piece of filter paper (0465) in half. Fold in half again. Gently push corners together to form a cone. Place cone in funnel (0459).

4. Place funnel in clean filtrate tube (0749) and filter suspension through the filter paper. The clear solution is the extract.

5. Use the 1 mL pipet (0354) to transfer 1 mL of soil extract to one of the depressions on the spot plate (0159).

6. Use pipet (0392) to add 10 drops of *Nitrate Reagent #1 (5146) 7. Use the 0.5 g spoon (0698) to add one measure of *Nitrate Reagent #2 (5147). Stir thoroughly with

plastic rod. Wait 5 minutes. 8. Match sample color to a color standard on the Nitrate-Nitrogen color chart (1315). Record your

measure as lb/acre nitrate-nitrogen.

Soil Nitrogen Data and Analysis

Table 7. Nitrogen Data:

Our Data Class Data

Sample Nitrogen Nitrogen

Garden Bed

Lawn

Questions:

1. What is the specific molecular form of nitrogen in this test?

2. Describe at least 2 pathways that this nitrogen could have taken to move from atmospheric (N2) to the current form.

3. Is the level of nitrogen adequate for most vegetables? If not, what could you do to fix it?

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Soil Phosphorus

Young plants absorb large amounts of phosphorus, which speeds seedling development and promotes early root formation. Rapid, early growth means hardier, stronger plants. In mature plants phosphorus is vital to the development of healthy seeds and fruit which contain large amounts of this essential nutrient. Only a small percentage of soil phosphorus is in available form and these phosphates move more slowly through the soil than other nutrients.

Instructions Soil Phosphorus

You will be using the Lamotte Phosphorus Module for Soil Macronutrients Kit. These are the directions that go with that kit. All materials should be stored in and returned to the blue kits when finished.

NOTE: This test is very sensitive to contamination. The work area, materials, and hands should be clean. Avoid exposure to fertilizer dust!

1. Fill a test tube (0755) to line 7 with *Universal Extracting Solution (5173) 2. Use 0.5 g spoon (0698) to add 4 level measures of soil. Cap and shake for one minute. NOTE: when

adding samples with high concentrations of carbonates to *Universal Extracting Solution (5173), swirl tube to mix for 30 seconds before capping to allow gases to escape.

3. Fold a piece of filter paper (0465) in half. Fold in half again. Gently push corners together to form a cone. Place cone in funnel (0459).

4. Place funnel in clean filtrate tube (0749) and filter suspension through the filter paper. The clear solution is the extract.

5. Fill the small graduated cylinder with 2.4 ml with soil extract. 6. Add 6 drops of *Phosphorus Reagent #2 (5166). Swirl to mix. 7. Add one *Phosphorus Test Tablet (5706A). Cap with Parafilm and swirl until the tablet disintegrates. 8. Remove cap. Hold tube ½” above the white area of the Phosphorus Color Chart (1312). Looking down

through the solution, match sample color to a color standard. Record as lbs/acre phosphorus. ** The color comparison should be done in natural light DO NOT ALLOW THE SOLUTION TO STAND FOR MORE THAN 10 MINUTES BEFORE MAKING THE COLOR COMPARISON

Soil Phosphorus Data and Analysis

Table 8. Phosphorous Data:

Our Data Class Data

Sample Phosphorus Phosphorus

Garden Bed

Lawn

Questions:

1. What does mean to say that the phosphorus is not in an “available” form?

2. Why is phosphorus often a limiting factor in ecosystems?

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Soil Potash (Potassium)

Potassium acts as a catalyst, a chemical agent that facilitates a number of chemical processes in the plant. Potassium promotes various aspects of plant metabolism – photosynthesis, efficient use of water and the formation of strong roots and stems. Well described as a “tonic” for plants, potassium strengthens natural mechanisms for the resistance of disease and extreme weather. Potash is pronounced Pot-ash rather than as Po-tash.

Instructions Soil Potash/Potassium

You will be using the Lamotte Potassium Module for Soil Macronutrients Kit. These are the directions that go with that kit. All materials should be stored in and returned to the blue kits when finished.

1. Fill a test tube (0755) to line 7 with *Universal Extracting Solution (5173) 2. Use 0.5 g spoon (0698) to add 4 level measures of soil. Cap and shake for one minute. NOTE: when

adding samples with high concentrations of carbonates to *Universal Extracting Solution (5173), swirl tube to mix for 30 seconds before capping to allow gases to escape.

3. Fold a piece of filter paper (0465) in half. Fold in half again. Gently push corners together to form a cone. Place cone in funnel (0459).

4. Place funnel in clean filtrate tube (0749) and filter suspension through the filter paper. The clear solution is the extract.

5. Fill a clean test tube (0755) to line 3 with soil extract. 6. Add one *Potassium Reagent B Tablet (5161). Cap and shake until tablet disintegrates. 7. Add *Potassium Reagent C (5162) to line 7. Allow it to run slowly down the die of the tube. Cap and

mix gently. A precipitate will form if potassium is present. 8. Place a Potash Tube “B” (0246) on the Potash Reading Plate (1107) directly over the black line. NOTE:

Face a window or some other source of daylight. 9. Use a pipet (0364) to add the treated test sample slowly to Tube “B” allowing it to run down the sides of

the tube while observing the black line through the solution. Continue until the line just disappears. 10. The height of the column of test sample is measured against the potassium scale on the tube. Record as

lbs/acre of potassium. NOTE: For extremely high readings, dilute the filtered extract and retest. Add the soil sample filtrate to line 3 of a clean test tube (0755). Dilute to line 6 with *Universal Extracting Solution (5173). Test following the procedure beginning with Step 5. Multiply final reading by 2.

Soil Potash/Potassium Data and Analysis

Table 9. Potassium Data:

Our Data Class Data

Sample Potassium/Potash Potassium/Potash

Garden Bed

Lawn

Questions:

1. Describe 2 sources of potassium for a soil that is depleted in this macronutrient. One should be from an organic (recently living organism) and one from a mineral source.