SOIL -- BEYOND JUST DIRT

Why do trees need good soil?

1. Structural support
2. Nutrients
3. Water
4. Oxygen

Image :http://wiki.ubc.ca/

The roots of trees are in the top 6 to 9 inches of soil. In the forest trees receive the four things listed above naturally. In an urban environment good soil is hard to find. In most urban sites I have found compacted soil, soil that has been leached of all the nutrients, or sites that have had all the top soil stripped away.



Soil horizons


O horizon-  Organic material- made up of leaves, wood breaking down, worms and insects.


A horizon-(top soil)  Mix of organic and mineral matter- made up of iron, clay, aluminum, and organic compounds.


B horizon- Sub soil-  made up of iron, clay, and aluminum.


C horizon- Parent rock- large pieces of rock.


E horizon - Bedrock 


In central North Carolina the A horizon is slim to none. If you have tried to dig in your yard in central NC you have seen the maybe inch of O and A horizon on top of hard red NC clay (B horizon).

Soil sample showing the O horizon, A horizon and B horizon. Sample was taken from a wooded area in central NC.

Soil elements and pH levels

The elements found in soil for a healthy tree are:

Primary- 

• Nitrogen-N
• Phosphorus- P
• Potassium-K 

Secondary-

 

• Calcium - Ca
• Magnesium- MG
• Sulfur- S

Micro nutrients- 

• Boron 
• Chlorine
• Cobalt
• Copper
• Iron
• Manganese 

For the best absorption of nutrients into the roots of trees the soil pH should be between 6.2 and 7.3.