jbgruver - 2/27/2021 11:22

Hi Mike,

Mineral soils with high clay content normally have the highest total porosity... in contrast high sand soils tend to have much lower total porosity.

As a result high clay soils hold on to much more water than high sand soils.

In terms of soil function, total porosity is much less important than the volume and connectivity of macropores (big pores that drain rapidly and allow most of the movement of air and water in soil) and the volume of large micropores that hold plant available water.

High sand soils tend to have a high volume of macropores but a relatively small volume of large micropores.

Silt loam soils with good structure tend to have the best balance of macroporosity (drainage) and large microporosity (plant available water).

High clay soils hold more water than silt loams but less of this water is plant available.

Joel
WIU Agriculture

BTW I just learned that one of my former students who is now a grad student at SD State played a key role in developing the cotton strip test that you recently posted about. I will email you off list about this.