EXPERIMENTS ON SOIL
Materials required: Measuring cylinder, water, soil sample.
Method:
- Add 200cc of water to 20cc of soil.
- Shake thoroughly and then leave to settle.
- Measure depth of the layers that settle out.
Observation: Humus floats, clay particles are suspended above a clay layer which is above a sand layer. Small stones settle at the bottom.
Conclusion: The particles settle according to their density and surface area.
To show drainage, permeability (porousity) and water retention capacity of a soil:
Materials required: Two funnels, sandy soil, clay soil, glass wool, water, two measuring cylinders, stop clock, two clamp stands.
Method:
- Plug the funnels on a clamp stand with glass wool.
- Half‑fill each of them with each of the soil samples.
- Cover both funnels with the same quantities of water,
- Use a measuring to collect water that runs through the soil samples for ten minutes.
Observation: More water is collected in the measuring cylinder under sandy soil than in that under clay soil. Conclusion: Sandy soil has higher permeability (porousity) and drainage than clay soil. Clay soil has higher water retention capacity than sandy soil.
To determine the pH value of a soil sample:
Materials required: Soil sample, petri dish, BDH indicator.
Method:
‑ Place a pinch of soil on a petri dish
‑ Soak it with BDH Universal Indicator and leave for 3 minutes.
‑ Tilt the petri dish so that the indicator drains out of the soil.
- Compare the colour of the indicator with the chart on the indicator solution bottle.
Observe and conclude the pH of the soil sample.
To determine the water rise or capillarity of a soil:
Materials required: 3 glass tubes, trough, muslin material, threads, 3 clamp stands, sandy soil, clay soil, loam soil.
Method:
‑ Pack‑fill each glass tube with a sample of dry soil.
‑ Cover one end of the tube with muslin material and tie it securely with a thread.
‑ Support the tubes with clamp stands with the muslin ends in water in a trough.
Observation:
After one hour sandy soil had higher rise but after one day, clay soil had the highest capillary rise.
Conclusion:
Clay soil has the highest capillarity followed by loam soil and sandy soil has the lowest capillary rise.
To show that soil contains living organisms:
Materials required: Test tubes, limewater, string, cork, soil samples, oven.
Method:
- Tie the soil sample in a muslin bag.
- Suspend the muslin bag using a string in a test tube containing some limewater.
- Cork the test tube.
- Arrange a control using a soil sample baked in an oven for 30 minutes.
Observation: The limewater in the test tube with unbaked soil turns milky while that in the test tube with baked soil does not turn milky.
Conclusion: Soil contains living organisms that respire to release carbon dioxide.
To determine the percentage of air in a soil sample:
Materials required: Soil sample, measuring cylinder, water, stirring rod.
Method:
- Put the soil sample in a measuring cylinder and record its volume A.
- Add water of known volume B.
- Stir and record the final volume C.
Observation: After stirring the level falls.
Conclusion: The soil sample contained air of volume (A+B) ‑ C.
Calculation:
Volume of soil sample = A
Volume of soil + water = A+B
Volume after stirring = C
Volume of air in soil sample = (A+B)‑C
%age of air in sample = (A+B)‑C x 100
A
To determine the percentage of water in a soil sample:
Materials required: Soil sample, beam balance, tray, evaporating basin (crucible), sieve, oven, dessicator.
Method:
‑ Spread freshly collected soil in a thin layer on a tray.
‑ Leave at room temperature until air‑dry.
‑ Pass the air‑dried soil through a sieve to remove stones.
‑ Put the air‑dried soil in a weighed evaporating basin or crucible and weigh both.
‑ Place the crucible in an oven at I00°C for 24 hours.
‑ Remove the crucible from the oven and allow it to cool in a dessicator.
‑ Weigh the crucible with the soil sample.
‑ Repeat the procedure until a constant weight has been attained.
‑ Keep the dried soil sample for further analysis.
Observation: The soil sample finally attains a constant weight.
Conclusion: The weight reduced due to loss of water by evaporation.
Calculation:
Weight of crucible = A
Weight of crucible + soil = B
Const. wt. of crucible + soil
after heating at 100°C = C
Weight of soil sample = B - A
Weight of water in soil sample = B ‑C
%age of water in soil sample = B - C x100
B - A
OR:
Weight of soil before heating = P
Constant weight of soil after heating at 100°C = Q
Weight of water in soil sample = P - Q
%age of water in soil sample = P - Q X100
P
To determine the percentage of humus in a soil sample:
Materials required: Soil sample kept from previous experiment, beam balance, crucible, oven, dessicator.
Method:
‑ Use the oven dried soil sample whose weight was P when air‑dry and Q after oven‑drying at 100°C to remove water.
‑ Put the oven‑dried soil sample in a crucible and heat in an oven to red‑hot at 400°C.
‑ Cool it in a dessicator and weigh again.
- Repeat the procedure until a constant weight R is achieved.
Observation: The soil has further reduced in weight.
Conclusion: The weight reduced after heating at 400°C is due to the loss or oxidation of humus.
Calculation:
Weight of air‑dried sample = P
Constant weight of oven‑dried
soil sample after heating at 100°C = Q
Constant weight of oven‑dried
soil sample after heating at 400°C = R
Weight of humus in soil sample = Q - R
%age of humus in soil sample = Q - R x 100
P