Ecology Lab (BIO357)

Lab One (Part Three)                                                                         Lab Sampling

In this lab we will be going we are going to make measurements on the samples we brought back from the field.  As with the field trip, we will divide up into small groups and each group will focus on a particular procedure.  An outline of the procedures has been prepared.  Please, become familiar with all the procedures before lab.  These procedures will use the two soil cores collected in the last lab.  One core will be used to determine soil texture and the other to determine soil chemistry.  Soil chemistry will include measurement of the pH and the amount of Nitrate, Phosphorus, Potassium and humus in the soils.  As a final note, these are all standard procedures for measuring soil properties.  When writing up the methods for your lab report, you do not need to outline all the procedures written here.  You can state that soil texture was measured as the relative abundance of gravel, sand and silt/clay.  Soil pH and nutrients were measured with a LaMotte Model STH-5 Soil testing Outfit using the methods provided.  Remember: you need to provide enough information such that another ecologist could repeat your studies.  A good rule of thumb in writing procedures, if the procedures are standard mention the procedure, but do not go into detail.  If the procedure is unique, new or unusual, then mention it in more detail.

Procedures: Soil Texture

Soil Texture is measured by comparing the relative abundance of the various sizes of soil particles.  Typically, when on talks about the soil texture, they are referring to the proportion of gravel, sand and silt/clay in a sample.  Soil texture is measured by shaking a dry soil sample through a series of increasingly finer sieves and weighing each fraction.  The total weight of the sample is taken as the sum of all the fractions.  The percent gravel is the proportion of soil found in the larger screens (#5, 10 and 35).  The percent sand is the proportion found in the smaller screens (#60, 120, and 230).  And the percent silt/clay is the proportion of soil found in the bottom tray. 

1.    The soil should be completely dry.  Gentle crumble the soil into its finer particles.  Separate out and remove any plant or animals material.

2.    Add soil to the sieve sequence and commence shaking (about 2 minutes).  The different soil particles will pass through the screens until stopped by the screen.

3.    Place the contents of each sieve into a weigh boat and weigh it.  Record your weights in the table at the back of the lab. 

4.    Calculate the %gravel as the total weight of materials in the #5, 10 and 35 sieves, divided by the total multiplied by 100%.  The % sand is calculated as the total weight in #60, 120 and 230 sieves, divided by the total and multiplied by 100%.  The %silt/clay is calculated as the weight in the bottom sieve, divided by the total and multiplied by 100%.

Test Procedures: pH

PH is a measure of acidity or alkalinity.  Soils can have a pH from 3.5 to 11.0, but plants grow well in the range of 5.0 to 8.5.  In soils with a low pH (acidic), some nutrients can reach toxic levels and the activity of soil microbes is greatly reduced.  Soils with a high pH (alkaline) generally have a lower micro-nutrient availability and some levels may be deficient.

1.           Fill the test tube (0204) approximately one-third full of soil.  Use the Demineralizer Bottle (1155) to add demineralized water to the tube, until it is filled to one-half inch from the top.  Cap and shake until the soil is well dispersed.

2.           Add 5 drops of Soil Flocculating Reagent (5643WT).  Cap and shake to mix.  Allow contents to settle before proceeding to Step 3.

3.           Use a 1 mL pipet (0354) to transfer 1 mL of the clear solution above the soil to one of the large depressions on a spot plate (0159).  Transfer a second 1mL sample to the other large depression on the spot plate.

4.           To the first sample on the spot plate, add two drops of Duplex Indicator (2221).  Compare the resulting color reaction against the Duplex Color Chart (1313).

5.           The wide range pH test result indicates which narrow range indicator and color chart should be selected to perform a more precise pH test.  Choose the narrow range indicator and appropriate chart with a mid-point that is as close as possible to the value obtained in the wide range test.

6.           Add two drops of the chosen narrow range indicator to the second sample on the spot plate.  Compare the resulting color reaction against the appropriate color chart to obtain a precise soil pH reading.

Test Procedures: Soil Chemistry (Nitrate nitrogen, Phosphorus, Potassium and humus)

Part One: Extraction

The following extraction procedure uses *Universal Extracting Solution (5173PS) to produce a single soil extract that is used in each of the following tests:  nitrate, phosphorus, potassium, and humus.

1.           Fill an Extraction Tube (0704) to the 14 mL line with *Universal Extracting Solution.

2.           Use the 0.5 g spoon to add eight level measures of the soil sample.  Cap and shake for one minute.

3.           Use a piece of filter paper and a plastic funnel to filter the soil suspension into a second extraction tube.  (Fold the filter paper in half and then in half again to form a cone that is fitted into the funnel.)  The filtrate in the second extraction tube is the general soil extract for use in the individual test procedures listed previously.

Part Two: Nitrate nitrogen

1.           Use a 1 mL pipet to transfer 1mL of the general soil extract to one of the larger depressions on a spot plate (0159).

2.           Add 10 drops of Nitrate Reagent #1 (5146).

3.           Use a 0.5 g spoon to add one level measure of Nitrate Reagent 2 Powder (5147).

4.           Stir thoroughly with a clean stirring rod.  Allow to stand five minutes for full color development.

5.           Match sample color with the Nitrate Nitrogen Color Chart (1315).  The result is given as pounds per acre nitrate nitrogen.  Multiply your result by 0.11 to convert to grams per meter².

Part Three: Phosphorus

***This test is extremely sensitive.  Special precautions should be taken to prevent contamination.

1.           Use a transfer pipet to fill a “Phosphorus B” Tube to the line with the general soil extraction.

2.           Add 6 drops of Phosphorous Reagent 2 (5156).  Cap and shake to mix.

3.           Add one Phosphorous Reagent 3 Tablet (5157).  Cap and shake until dissolved.

4.           Immediately compare the color that develops in the test tube against the Phosphorous Color Chart.  Hold the tube about one inch in front of the white surface in the center of the chart.  View the chart and sample under natural light for optimum color comparison.  The test result is read in pounds per acre Available Phosphorous.  Multiply your result by 0.11 to convert to grams per meter².

Part Four: Potassium

1)           Use a transfer pipet to fill a Potash “A” Tube (0245) to the lower line with the general soil extract.

2)           Add one Potassium Reagent B Tablet (5161).  Cap and shake until dissolved.

3)           Add Potassium Reagent C (5162) until the Potash “A” Tube is filled to the upper line.  Allow the Potassium Reagent C to run slowly down the side of the tube.  Swirl the tube to mix.  A precipitate will form if potassium is present.

4)           Stand the empty Potash “B” Tube (0246) on the Potassium Reading Plate, a rectangular piece of white plexiglass with a solid black line down the middle.  Place the tube directly over the black line.

5)           Fill a transfer pipet with the test sample from the Potash “A” Tube.

6)           Slowly add the test sample to the Potash “B” Tube, allowing it to run down the side of the tube.  Observe the black line down through the Potash “B” Tube.  Continue to add the test sample until the black line just disappears.

7)           Record the value where the level of the liquid meets the scale printed on the side of the Potash “B” Tube, as pounds per acre Available Potassium. 

8)           If the test result is equal to or greater than 400 pounds per acre, repeat the test on a diluted test sample as follows:

a)           Fill a Potash “C” Tube to the lower mark with the general soil extract.

b)           Add *Universal Extracting Solution to the upper mark and mix.

c)            Using this diluted extract follow Steps 1 through 7 above.  Multiply the test result by 2 to obtain pounds per acre Available Potassium.

9)    Multiply your result by 0.11 to convert to grams per meter².

Part Five: Humus

     Humus consists of the complex remains of fresh plant and animal residue after extensive chemical and biological breakdown.  It accounts for 60% to 70% of the total organic carbon in soils.

1.           Use the 0.5 g spoon to add four level measure of soil to a soil extraction tube.

2.           Use the Demineralizer Bottle to fill the tube to the 14 mL line with demineralized water.  Cap and shake to mix.

3.           Use a 0.5 g spoon to add two level measures of *Humus Screening Reagent Powder (5119).  If necessary, add more demineralized water to return the level of the liquid to the 14 mL line.  Cap and shake vigorously for one minute.

4.           Add 15 drops of Soil Flocculating Reagent (5643).  Cap and mix gently.  Allow to settle for several minutes.

5.           Use a piece of filter paper and a plastic funnel to filter the mixture into a second extraction tube.

6.           Compare the clear filtrate in the second extraction tube with the Humus Color Chart (1384).

Interpretation

The humus color comparator is labeled with values of 1,2,3,4, and 5.  The results are interpreted as follows: