1. Soils and Growing Media
5.02 Discuss the soil profile and soil sampling for surface and subsurface layers

2. Soil Profile Layers of soil are called horizons:
O Horizon – Organic Matter (2”)
A Horizon – Topsoil (4”)
(most fertile, most organic matter, top or first layer).
Most smaller plants and grasses only grow in top 6” of soil.
B Horizon - Subsoil.
C Horizon - Parent Material
R Horizon - Bed rock

3. Soil Profile
All soil profiles do not have the same number or level of horizons
For example, a sandy soil may not have an “O” horizon if it has been under cultivation
Other soils may have a horizon missing due to erosion.
Most typical soils in NC will have a minimum of the A, B, and C or R horizons

4. Soil Profile
O horizon
Rich soil found where a plant cover has been in place for an extended time
Rich in organic matter in various stages of decomposition and is dark in color
It is the most fertile layer in the soil profile

5. Soil Profile
A Horizon
Is the topsoil and most fertile in the absence of an O horizon
A horizon lies just below the O horizon and is home to earthworms and soil organisms
Brown in color due to organic matter in the soil

6. Soil Profile B Horizon The subsoil
Clayey soil that has high mineral content
Usually brown or reddish due to the large amount of clay

7. Soil Profile C Horizon R Horizon Parent Material
Consists mainly of clumps of un-weathered rocks
R Horizon
Bed rock
Cannot be dug by hand and very few roots can penetrate the bedrock

8. Soil Horizons

9. Soil Structure How particles cluster together.
Sandy soils have loose structure
Silty soils have granular
Clayey has blocky or platy
Granular is best.
Plants have good root development
Water movement is at an appropriate rate
Doesn’t stay too wet or too dry

10. Soil Texture = Size of Particles
Sand
Clay
Silt

11. Sand
Large particles, low moisture and nutrient holding capacity.

12. Silt Medium sized particles and good moisture and nutrient
holding capacity.

13. Clay
Small particles
Has high water and nutrient holding capacity.

14. Loam Loam has almost equal parts of sand, silt, and clay
This is the ideal texture for most non-container outside plants

15. Soil pH Measures the acidity or alkalinity of soils
Ranges from is considered an acid soil, 7 indicates a neutral soil, and 8-14 is considered alkaline
Lime will raise the pH value (make it less acidic)
Calcium or sulfur will lower the pH value (make soil more acidic)

16. pH Ideal pH for most ornamental plants and turf is 5.5 to 7.0 Acid
Acid
Basic (alkaline)
Neutral

17. Other Soil Properties
Permeability is the rate at which water moves through the soil
Water holding capacity is the ability of a soil to hold water for plant use
Porosity is the amount of air space between soil particles

18. Other Soil Properties
About 50% of soil should be solid particles. 45% mineral matter, 5% organic matter
About 50% of soil should be pore space. About 25% of pore space should be filled with water, 25% air space
Soil structure is more important to producers who grow plants in natural soils because producers of container grown plants add ingredients to make growing media desirable.

19. Soil Sampling
Is essential for an accurate fertilizer recommendation for growing plants
Soil sampling procedures:
Create a visual grid of the area to be planted
For gardens and landscapes, take 5-10 subsamples from the site to be evaluated
Sample before the growing season

20. Soil Sampling Procedures: Use a stainless steel soil-sampling probe
Take the surface sample to tillage depth or about 3-4 inches for lawns, and 6-8 inches for crops
Mix the soil samples together

21. Soil Sampling Remove any grass, rocks or other material besides soil
Avoid unusual spots in the lawn or field.
Those areas need to be sent in a separate box
Place soil samples in a box, which you can obtain form the County Extension Office with Soil sample information sheet
Send the box and information to Agronomic Division Soil Test Lab in Raleigh for a free soil test