Editing Soil structure (section)

===Columnar===

In the columnar structure, the units are similar to prisms and are bounded by flat or slightly rounded vertical faces. The tops of columns, in contrast to those of prisms, are very distinct and normally rounded. Columnar structure is common in the subsoil of sodium affected soils and soils rich in swelling clays such as the [[smectites]] and the kandite [[Halloysite]]. Columnar structure is very dense and it is very difficult for plant roots to penetrate these layers. Techniques such as deep plowing have helped to restore some degree of fertility to these soils.