AP Environmental Science 12

Soil Lab

Name:Date:Block:

Objective

To test soils for their texture and chemical composition and to relate the results of these tests to the fertility of the soil

PART I: 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 clay, silt or sand. The soil texture triangle is a diagram often used to figure out soil textures once the proportion of clay, silt and sand is known.

Materials

1

100mL graduated cylinder

Soil sample

Water

Ruler

Procedure (Soil Texture)

1. Fill the graduated cylinder with approx. 25mL of your soil sample

2. Add 50mL of water to the graduated cylinder

3. Cover the graduated cylinder and shake the mixture well for about 2 minutes.

4. Allow the cylinder to sit and settle out

5. Once the soil has settled, there should be three distinct layers. Measure the volume of each layer and the total volume of the sample

Bottom Layer (Sand) Volume (mL)

Middle Layer (Silt) Volume (mL)

Top Layer (Clay) Volume (mL)

Total

Volume (mL)

6. Calculate the percentage of each layer and enter your results in the chart that follows

% Sand

% Silt

% Clay

7. Now, use these percentages and the soil texture pyramid below to identify the type of soil in your sample.

Using the soil texture pyramid, the soil texture is ___________________________________

8. In the field, soil analysis may be limited by time constraints. Follow the instructions in the chart Guide to Texture by Feel to determine the identity of your soil.

By feel, the soil texture is _____________________________________________________

Follow-Up Questions

1. What is the relationship between soil texture and the amount of water that can pass through?

2. What is the best type of soil for plant growth?

3. What are the causes of erosion?

4. What can be done about erosion problems?

5. Do you think your soil would be subject to erosion? Why or why not?

PART II: PERMEABILITY

Permeability is the amount of water that can flow through a soil. It is important for water to be able to travel through a soil so that the soil doesnt get waterlogged, but soils must also be able to retain (hold onto) water so that water is available for plant roots.

Materials

2 funnels

Soil sample

Sand sample

100mL graduated cylinder

Filter paper

Procedure (Soil Permeability)

1. Take two funnels and place filter paper in the bottom of each

2. Fill one funnel halfway up with soil

3. Quickly pour 100mL of water into the funnel

4. Record the time required for all the water to drip through the soil by stating the timer when you pour and ending when most of the water has percolated through the soil.

5. Repeat the procedure with pure sand.

Time

Soil

Sand

Analysis

1. How do the percolation times compare for soil and sand?

2. What does this tell you about your soil?

3. What type of soil has the fastest infiltration ratesand, silt or clay?

4. Why would a farmer need to know the soil permeability of his land?

PART III: POROSITY

The spaces that exist between soil particles, called pores, allow gases and moisture to collect and pass through soils. The soils ability to retain water is strongly related to the size of the particles that make up the soil. Water molecules hold more tightly to the fine particles of a clay soil than to the coarser particles of a sandy soil, so clays tend to retain more water.

The maximum amount of water that a given soil can retain is called the field capacity, whereas a dry soil is said to be at wilting point. Water available for plants is within the range of a soils field capacity and wilting point.

Materials

250mL beaker

100mL graduated cylinder

Soil sample

Procedure

1. Fill a 250mL beaker with soil to the 200mL mark. Tamp it down gently.

2. Fill a 100mL graduated cylinder with 100mL of water

3. Gently pour all the water onto the surface of the soil until it is completely saturated and begins to pool on the surface

4. Measure the amount of water left in the graduated cylinder. The amount of water used is the amount of pore space in your sample.

5. Calculate the porosity of your soil

The porosity of this soil sample is: _____________________________

Follow-Up Questions

1. What soil texture will result in the most oxygen for plant rootssand, silt or clay?

2. If a soil has a high porosity, will it be able hold onto water? Explain.

PART IV: 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 (Na, K, P, etc.). These nutrients can then be leached from the soil.

Procedure

1. Follow the directions in the soil test kit to test the pH.

The pH of this soil sample is: _____________________________

Follow-Up Questions

1. Was your soil acidic, basic or neutral?

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

3. How does pH influence the fertility of soil?

PART V: 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 worlds food supply. Nitrogen is directly involved in photosynthesis. It stimulates above ground growth and produces the rich green color characteristic of healthy plants. Nitrates, the available form of soil nitrogen, are produces 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.

Procedure

1. Follow the directions in the soil test kit

The nitrogen level of this soil sample is: _____________________________

Follow-Up Questions

1. What could you do to increase the nitrogen levels of your soil?

PART VI: 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 (phosphates) and phosphates move more slowly through the soil than other nutrients.

Procedure

1. Follow the directions in the soil test kit

The phosphorus level of this soil sample is: _____________________________

Follow-Up Questions

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

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

PART VII: 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 metabolismphotosynthesis, efficient use of water and the formation of strong roots and stems. Potassium strengthens natural mechanisms for the resistance of disease and extreme weather.

Procedure

1. Follow the directions in the soil test kit

The potash level of this soil sample is: _____________________________

Follow-Up Questions

1. Besides fertilizer, how does potassium get into the soil?