Environmental Engineering Reference
In-Depth Information
Waterlogged soils form the basis of the paddy system of rice cultivation in many tropical
and subtropical regions. The typical soil profile of a rice paddy is shown in Figure 19.11.
The sheet of water at the soil surface supports algae, which keep the water oxygenated
and some of which are able to fix atmospheric nitrogen. Below it is a brown aerobic
horizon and below that a thick blue-grey gleyed layer.
High-yielding varieties of rice require a high level of nitrogen. Nitrates which form in
the surface soil layer are able to diffuse into the anaerobic reduced soil horizon below.
Here they are reduced to the nitrogen (N
2
) and nitrous oxide (N
2
O) gaseous forms and are
lost to the
Figure 19.10
A luvisol soil, showing the effects of clay
translocation.
