Soils Lab

 

Introduction:  The anchor for all ecosystems is the producer level upon which all other consumers depend.  Providing the nutrients, water and other requirements for these producers is the soil.  Soil also helps to purify the water we drink, aids in decomposition and recycling of biodegradable materials.  In this lab we will investigate several soil properties.

 

Water Infiltration and Retention- The soils ability to absorb and hold water and nutrients is critical to the growth of plants and to environmental problems such as flooding and leaching.  For example clay soils hold nutrients well but swell when water is applied and then shrink and crack as the water is removed.  Sandy soils do not retain water but offer air spacing for plants.  Optimum soil conditions have mixtures of the three main soil components.

 

Retention-

To determine water retention-

1.      Mass a watch glass or other suitable holder.

2.      Add sand, silt or clay. Mass and then moisten, mass again.

3.      Dry in an oven for 1 hour (overnight if possible).

4.      Mass the samples again after drying.

5.      Calculate the water holding capacity as :

[(Dry – Oven Dry ) / (Wet  - Oven Dry) ] x 100 = WHC

 

Density- Dense soils have high strength, low porosity and poor plant growth potentialoils can become more dense due to compaction of heavy equipment or animal traffic.

  1. Weigh out 15 grams each of your available soil samples.
  2. Pour into a graduated cylinder and gently tap the cylinder to settle the particles.
  3. Measure the volume of the soil samples.
  4. Determine the bulk densities in g/cm3

Rank the samples on the basis of density:

 

 

Infiltration-

1.      Obtain three soil samples- topsoil, clay, sand or available samples.

2.      Half fill the funnel with the soil sample.

3.      Add approximately 20 mL of water to the funnel and record the time it takes to recover the water sample.

4.      Rank the relative rates for the samples provided.

 

 

 

 

 

 

Soil Texture-  Weathering breaks down rocks into fine particles of clay (0.002 mm), silt (0.002 to 0.05 mm) and sand (0.5 to 1.0mm).  The relative amounts contribute to soils ability to hold nutrients and water.

1.      Place 20 mL of your soil sample into a 100 mL graduated cylinder.

2.      Fill the cylinder to app 80mL line.

3.      Cover the cylinder and shake vigorously.

4.      Let stand for 5 minutes for the soil to settle.

5.      Estimate the volumes of each and record as % of total volume for clay, silt and sand.

6.      Use the soil texture diagram to determine the kind of soil in your sample.

7.      Clean out your graduated cylinder and discard the soil sample where instructed.

 


 

 

Soil pH- Acidity also plays a role in sole quality.  In general more acid soils have lower fertility than basic soils because positive H+ ions displace the positive K+, NH4+ etc. ions.  Calcium ions decrease soil acidity, hence a common approach of gardeners and farmers is to add “lime”  a source of  calcium.

1.      Place a sample of soil into the small graduate and fill with distilled water.  Shake and allow to settle for several minutes.

2.      Using pH paper test the water solution above the soil.  Pour off several mL for use in phosphorous testing.

3.      Does the soil source alter the pH?  Explain your reasoning for the differences.

 

 

Soil Nutrients- Soil fertility is measured by the amount of available nutrients.  Common nutrients are ammonium ions, calcium ions, potassium ions and phosphate ions.  These positive nutrients are held by negative charges.  Clay has negative charges while sandy soils do not.  Therefore soils with clay retain nutrients better than those without clay.

 

Nitrogen-

1.        We will use a nitrate ion probe to test for nitrate levels.

2.        Most agricultural crops require nitrate levels above 300 mg/L.

Determine the nitrogen levels of your soil samples.

 

Phosphorous-

1.   Place 2 mL of a control solution into a test tube and add 1 mL of Fe(NO3)3 solution.             A light brown precipitate should form.  Place 2 mL of soil sample from pH test step 2 into a small test-tube.

2.       Add  1mL of Fe(NO3)3 solution to your soil sample.   Check for a light brown precipitate.

 

 

Conclusion:

1.      Summarize your results in a table indicate the type of soil its retention and infiltration rate, density,  pH, nitrogen and phosphorous levels.  Rate the soils tested for their best use.

 

2.      Design three soils which would be classified as sandy loam, silty clay and clay loam.  Use the soil texture Chart.

 

3.      Modern sanitary landfills often use layers of soil to “seal” individual daily layers of

refuse,  which type of soil would you recommend?  Why?

 

 

4.      Briefly discuss how erosion and nutrient loss have become important soil conservation  issues to the  agriculture industry.