When rain falls, water passes through the soil, washing minerals, humus and nutrients from the A horizon down into the B horizon. This process is called leaching.
Most plant roots are located in the A horizon, and leaching can sometimes interfere with their growth if nutrients are washed beyond their reach.
Sometimes, in extremely wet conditions, minerals build up at the bottom of the A horizon. They can become cemented together to create hardpan. This is an impermeable layer that water is unable to flow through, and so the soil above the hardpan becomes waterlogged.
Impermeable:
something that will not allow water to pass through it.
: Figure 16.5 Hardpan Hardpan
: Figure 16.6 Soil profile showing where nutrients have been leached out of the grey layer
(i) Name the five ingredients of soil. (ii) What percentage of a typical soil sample is water? (iii) What is humus? (iv) Explain the term leaching. (v) Explain how a hardpan is formed. (vi) Draw and label a soil profile in your copybook.
/ I can explain what the five ingredients of soil are. / I understand what soil texture is. / I can draw and label a soil profile. / I can explain leaching.
