1. Paul Snyder, Secrest Arboretum, OARDC
What’s the Dirt on Soil?
Paul Snyder, Secrest Arboretum, OARDC

2. Why is soil important?

3. It supports life.
Living things need the proper temperature, oxygen, water, carbon and other nutrients.

4. What is soil?

5. How is soil made? Parent Material Weathering/Erosion Organic material
Soil Microorganisms
Bacteria, fungi, lichens, nematodes
Organic material

6. Parent Material Bedrock Igneous Sedimentary Metamorphic
Formed by the cooling and solidification of molten materials deep in the earth. (I.e. granite)
Sedimentary
Forms when loose material such as sand or mud are deposited by water or wind, are slowly cemented by chemicals and/or pressure into rock. (i.e. shale)
Metamorphic
Formed when igneous or sedimentary rock are subjected to heat. (i.e. marble)

8. Glacial deposits Wind deposits Water deposits Sand, gravel, clay
Loess soils
Wind deposited silt particles
Water deposits
Alluvial soils
Parent material was carried and deposited by moving fresh water.
Marine deposits

9. Volcanic ash Organic deposits Contain more than 20% organic matter.
Form under water as aquatic plants die.

10. Soil horizon Horizons are layers found within the soil
Soils change over time in response to their environment.
As soils age, minerals and smaller particles leach down to create a new horizon.

11. A: Topsoil. Surface mineral layer where organic matter accumulates
O: Organic matter. Made up completely of decayed plant and animal matter.
A: Topsoil. Surface mineral layer where organic matter accumulates
Best environment for microorganisms and roots.
E: zone of maximum leaching (iron, clay, and other minerals). Usually found in forest soils.
B: subsoil. The zone where minerals and particles from the A and E horizons accumulate.

12. C: The parent material. Lacks the properties of A and B horizons
C: The parent material. Lacks the properties of A and B horizons. Little touched by soil forming processes.
May include bedrock or other parent material
R: the bedrock.

15. Soil texture Soil texture is the proportion of three soil particles.
Sand: large
Silt: medium
Clay: small
Soil texture influences all other soil traits.

16. Macropores: largest pores.
Largely determine the movement of air and water through the soil.
Micropores: small pores
Retain water as it drains through the soil.

18. Silt

21. Nutrients and pH Macronutrients Micronutrients Chlorine Nitrogen Iron
Phosphorus
Manganese
Molybdenum
Potassium
Micronutrients
Nickle
Zinc
Calcium
Sodium
Magnesium
Silicon
Sulfur
Cobalt
Boron
Copper

23. Cation Exchange Capacity
Cation Exchange Capacity (CEC)
Refers to the soils ability to gain and hold nutrients (ions).
Clay and hummus hold cations.
High CEC: units (cmol/Kg)
Low CEC: less than 11
CEC influences fertilizer application
What type of soil has a high CEC?

27. Soil Compaction Occurs when pressure is applied to the soil surface.
Reduces the pore space
Can also crush soil aggregates.
Changes soil porosity and permeability.
Loss of macropore space
Loss of pathways for gas and water movement.
Wet soils are more prone to compaction than dry soils.
Soil particles slide past each other more easily.

28. Soil Compaction: Effects
Reduced porosity and permeability
Reduced air exchange.
Reduced soil available water.
Decreased water infiltration
Increased erosion due to greater run off
Restricted root growth

29. Soil Compaction: Plants
Plants try to compensate for compacted soil by changing their growth habits.
Roots are less branched and thicker.
While this protects roots from soil pressure, it decrease root function
Decreased ability to absorb water and nutrients

30. Tilling can alleviate soil compaction
Where tillage is not possible compaction presents a problem to many plant species.
Plow pans form as the result of repeated tillage operations.

32. Soil Amendments Amendments can help improve
Soil structure
Soil fertility
Drainage or water-holding capacity
Amendments should be incorporated into the top 4-6” of soil.
Layering effect of different textures
Can be tilled or incorporated by hand.
Soil may not need amended.

33. Use similar or native soil to backfill the hole.
Any organic amendments should not exceed the soil backfill by any more than 10% by volume.
Amend site soil as needed. (Usually not recommended). This allows the tree to establish into the native soil much faster. Why is it not sustainable to amend the entire site?
To have lasting impact you would need to amend a much larger site than just the planting hole.

34. Fungi
Mycorrhizae
Fungi that form a symbiotic relationship with plant roots that allows the plant to better absorb certain nutrients and water.
Mycorrhizae improve soil aggregation.
Ectomycorrhizae: Common on Woody Plants
Grow on the outer layers of cells
Endomycorrhizae: Common deciduous woody and herbaceous plants.
Grows inside plant cell walls.

35. Both types act as ‘extensions’ of the roots
Both types act as ‘extensions’ of the roots. Because fungal hyphae are thinner than roots they can penetrate small soil pores than root hairs.
Soil tillage disrupts fungal hyphae.
High phosphorus levels suppress mycorrhizae.
Most plants (65-95%) have mycorrhizal associations.

36. Soil Test Why should you soil test? Determine fertility needs
Levels may be too low, too high, or just right.
To make plant selections
To diagnose plant problems

37. When should you soil test?
Before planting
Before making plant selections
Before applying fertilizer
Samples can be taken any time of the year.

38. How to Collect Soil Samples
Use a soil probe or garden trowel
Take samples from the top 6-8” of soil
Remove organic matter (such as much/ grass) from soil sample.
Sample beds or law in a random, z or x pattern.
If sampling multiple garden beds, keep the samples separate.
Take samples from a given area.

39. Combine samples from similar area into a bucket Mix samples together.
Allow soil to dry at room temperature
Spread out on newspaper
Break into pieces the size of a grain of wheat.
Send sample to lab.

40. Sample A
Sample C
Sample B

41. Interpreting a Soil Test
Soil pH.
7 is neutral
6.5 is ideal for most plants.
5 is acidic
Above 7 is alkaline
Buffer pH (basically how easily can the pH be changed).
or Lime Test Index 68-70

42. Phosphorus (P) Potassium (K) Calcium (Ca) Magnesium (Mg)
30-60 Lbs/acre or ppm
Potassium (K)
Varies based on the CEC
Calcium (Ca)
800-16,000 lbs/acre or 400-8,000 ppm
Magnesium (Mg)
150-2,000 lbs/acre or 75-1,000 ppm.

43. CEC:11-50
Base Saturation
The extent to which a soil is saturated with exchangeable ions other than hydrogen or Aluminum
% Ca: 40-80
% Mg: 10-40
% K: 1-5