Soil fertility and conductivity
The materials required for this science fair project:
- 200g of sand
- 200g of clay
- 400g of loam
- 50ml of liquid fertilizer
- 800ml of water
- 4 beakers
- 1 DC12V battery
- 3 jumper wires with crocodile clips at both ends
- 2 copper electrodes
- 1 miliammeter
- 1 digital weighing scale
- 1 measuring cylinder
- 1 ruler
- 1 clock
1. For this science fair project, the independent variable is the type of soil used – sand, clay, loam and loam mixed with fertilizer. The dependent variable is the conductivity of the soil. This is determined by measuring the current conducted in the soil using a miliammeter. The constants (control variables) are the amount of soil in the beaker, the amount of water added, the temperature of the environment (which will remain at room temperature), the battery voltage and the distance between the electrodes.
2. Dry the samples of sand, clay and loam under the sun or in an oven, to remove moisture.
3. Label the 4 beakers ‘sand’, ‘clay’, ‘loam’ and ‘loam with fertilizer’. Measure out 200g of each type of soil and place in the appropriate beaker, Then, measure and add 200ml of water into each beaker. Add 50ml of liquid fertilizer to the beaker marked ‘loam and fertilizer’.
4. Leave the beakers aside for 30 minutes. This will allow the soil to absorb the water, as well as allow the mineral salts to dilute.
5. Insert 2 copper electrodes 5 cm apart in one beaker. Connect the ammeter and the DC12V battery to the electrodes. Record the current measurement in a table, as shown below.
6. Repeat step 5 with the remaining beakers.