Practical 3:Water Retention Capacity of soil

Practical 3: Water Retention Capacity of Soil

Picture 1. The crucibles before the first heating. (Loamy soil on the L.H. side and Clay soil on the R.H. side) Taken by Thomas Mudge on the 13/02/2014

Picture 2. The crucibles after the heating (Loamy soil L.H and Clay soil R.H). Picture taken by Thomas Mudge on the 16/02/2014

The results





Soil 1 is the Loamy soil. Soil 2 is the Clay soil

Conclusion

What can you conclude about the water retention capacity of your two soil samples?

The  Clay soil has better water retention capacity, because the first reading of the mass showed how much heavier the damp clay soil was than the damp loamy soil. The difference in the mass of the crucible was 0.7g. Taking this difference into account, there was still a difference of 3.7g, which we concluded was due to the extra water retained.

If you take the mass of the crucible out of the equation, the damp clay soil (no.2) weighed 10.2 grams and the same volume of damp loamy soil (no.1) weighed 6.5 grams.

It took longer for the clay soil to dry out.

After evaporation the loamy soil weighed 4.7 grams and the clay soil weighed 9 grams.

That means the loamy soil lost 1.8 grams of water and the clay soil lost 1.2 grams of water. Our results however were confusing, because if all the water was evaporated and that is what we were measuring, it appears from our results as though less water was retained in the clay soil, but we think this is because all the water didn't evaporate.

Questions:

 1. Which soil sample retained more water?

The Clay soil should have retained more water.

2. Which soil sample retained less water?

The Loamy soil should have retained less water.

3. Can you account/explain why there may be differences in water content between the two samples?

We think the clay soil would retain more water as this is the nature of clay soil. We believe not all the water evaporated. also there may have been less water added to the damp clay soil in the first place

4. Do you agree that the difference in mass between the two samples is the mass of water in the soil sample? Could it be anything else?

We believe the most likely explanation in the difference of mass is the water or moisture, because of the fact that we evaporated the moisture from the soil. However, at this temperature other changes could have taken place such as chemical changes.

5. What value is there in knowing the water content of your soil in your window farm?

It is important for a farmer to know how much moisture is in the soil, especially in a hot, dry area like the Western Cape is in summer. If a grower knows that the soil still has moisture he doesn't have to wet the soil, because the plant will be getting enough moisture already. This allows him to save money, water and energy costs. It is exactly the same with our window farm.

Discussion:

This practical was very interesting. It tested our lab skills and we learned a lot from that. What it was trying to demonstrate was that clay soil retains more moisture. However, our results were somewhat confusing. This gave us a concern and so instead of looking for a mixture of sol types for our window farm, we investigated alternatives. 

We spoke to a guy at the nursery and told him we want a potting soil that was rich in nutrients (like loamy soil), but had good drainage like sandy soil (as we plan to grow herbs) and also good water or moisture retention properties (like clay soils have).

He recommended a potting soil mixture that uses broken up cocconut husk which retains moisture, while still allowing drainage. This is mixed with a compost that is full of nutrients. This is what we used.