Agro/Hort 100 Intro to Plant Science

Soils

Soil Morphogenesis

Physical Properties of Soil

Chemical Properties of Soil

Soil Organisms

 


Physical Properties of Soil

  1. Soil Texture
  2. Soil Structure
  3. Soil Compaction

1. Soil Texture is the percent of sand, silt and clay in a soil.

The sizes of these particles fall into the following sizes:

Soils with specific ratios of these three particle types are usually represented on a Soil Textural Triangle.

 

Figure from GLOBE Teacher's Guide 1996

An ideal soil texture would be 40% sand, 40% silt and 20% clay.  Using the textural triangle what is the name for a soil with this composition?

Soil texture affects:

  • water retention
  • aeration
  • specific heat capacity
  • fertility or cation exchange capacity
  • tillage

 

image courtesy of Dr. Curtis Monger

1. Water Retention Sandy soils have the coarsest texture and therefore the largest pore sizes. These large pore sizes are too large to hold water through its cohesive property. Clay soils have the finest texture, therefore the smallest pore sizes. Clay soils are able to hold much more water because of their smaller pore size.
2. Aeration Sandy soils have the coarsest texture and therefore the largest pore sizes. These large pore sizes drain rapidly, and the sand particles do not compact, therefore these soils have the highest aeration volumes, and clay soils the lowest aeration volumes.
3. Specific heat capacity Because sandy soils hold very little water, they warm up faster in the spring and cool down sooner in the fall. In contrast, clay soils with higher water content, have high specific heat capacities. They warm up slower in the spring and cool down slower in the fall.
4. Fertility Clay soils have a greater surface area per volume and a higher cation exchange capacity and therefore are able to hold more ionized minerals or nutrients. Sandy soils have a lower cation exchange capacity and are able to hold fewer nutrients.

image courtesy of Dr. Curtis Monger

5. Tillage Because clay soils have the finest texture, they are harder to till and more likely to become compacted.


[Soils] [Agro/Hort 100] [Agro/Hort 100 Syllabus]


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Last Updated: February 9, 2001 Error: Unable to read footer file.