Soil Water Holding Capacity

This experiment measures how much water a soil sample can retain after being saturated and drained. By comparing the dry and hydrated weights of a soil sample, students can calculate its water holding capacity and understand how soil composition affects water availability for plants.

1. Spread a collected soil sample evenly on a baking tray to a depth of about 0.5 cm.
2. Place the tray in an oven or incubator set at 105°C and dry the soil completely.
3. Using heatproof gloves, remove the tray and allow the soil to cool to room temperature on a heatproof surface.
4. Weigh an empty 100 mL beaker and then zero the scale.
5. Add about 50 g of the dried soil into the beaker and record the exact initial weight.
6. Set up a funnel on a retort stand and insert filter paper inside the funnel.
7. Transfer the 50 g of dry soil into the funnel.
8. Place an empty 100 mL beaker beneath the funnel to collect any drained water.
9. Measure 100 mL of water in a measuring cylinder and pour it slowly over the soil in the funnel.
10. Cover the funnel top with cling wrap to minimize evaporation, and poke small holes with a toothpick to maintain air pressure.
11. Leave the setup overnight to allow drainage.
12. After draining, weigh the hydrated soil (still in the filter paper) and record the final weight.
13. Calculate the amount of water retained by subtracting the initial soil weight from the final soil weight.
14. Determine the water holding capacity as a percentage.
15. Repeat for other soil types.

Soil Water Holding Capacity Determination Practical Experiment - ThomasTKtungnung:

Water holding capacity - Chemistry with Mrs V:

📄 Water holding capacity of soil experiment - Gene Technology Access Centre: https://gtac.edu.au/wp-content/uploads/2022/02/Transpiration-water-holding-capacity-of-soil-experiment-v1.0.pdf

• Test different types of soil (clay, sand, loam) to compare water holding capacities.
• Use different soil particle sizes or organic content levels to see how they affect results.

• Use heatproof gloves when handling the hot oven, trays, or soil.
• Ensure all equipment removed from the oven is placed on a heatproof mat.
• Do not leave the oven unattended while drying soil.
• Avoid touching hot metal equipment directly.
• Handle glassware carefully to prevent breakage.
• Clean and dry all equipment thoroughly after use.

• Which type of soil would you expect to have the highest water holding capacity, and why? (Clay soils generally hold more water due to smaller particles and greater surface area.)
• Why must the soil be completely dry before starting the experiment? (To ensure accurate measurement of only the water added and retained.)
• What effect might organic matter have on the soil’s water holding capacity? (Organic matter increases water retention by improving porosity and binding water molecules.)
• How could soil structure influence plant growth and transpiration rates? (Soils with better water retention provide more consistent moisture for roots, supporting photosynthesis and transpiration.)
• Why is it important to prevent evaporation during the draining period? (To ensure any loss of water measured is due to drainage, not evaporation.)