1. Soils – what trees need to thrive
Meghan Midgley, PhD
Soil Ecologist, The Morton Arboretum
Transportation and Trees Workshop
March 2, 2017

2. Likely problems with roadside soils:
Compacted
Low nutrient availability
High salt loading
Due to location and road construction
soils are typically degraded
by processes intended to facilitate building construction, such
as vegetation clearing, topsoil removal, grading, and compaction

3. Overall goal: mimic natural soils

4. Overall goal: mimic natural soils
What are the characteristics of a forest soil?
More pore space
Organic matter
Structure

5. Soil compaction is the most prevalent of all soil constraints on road tree growth
Roots can’t penetrate

6. Soil compaction is the most prevalent of all soil constraints on road tree growth
Roots can’t penetrate
Low water availability

7. Soil compaction is the most prevalent of all soil constraints on road tree growth
Roots can’t penetrate
Low water availability
Not enough oxygen for roots

8. Soil compaction is the most prevalent of all soil constraints on road tree growth
Low water availability
Roots can’t penetrate
Not enough oxygen for roots
Too much carbon dioxide

10. Deep ripping alone is a short-term solution!

11. Soil profile rebuilding is a long-term solution
Spread compost 4 inches deep over the surface of the existing soil.
The process was developed by a Virginia Tech research group led by Dr. Susan Day. 

12. Soil profile rebuilding is a long-term solution
Spread compost 4 inches deep over the surface of the existing soil.
Use a backhoe to scoop a bucket of soil with compost on the top, lift it several feet in the air, and drop it.
Breaks up compacted soil into large clods
Creates veins of compost down 24 inches
The process was developed by a Virginia Tech research group led by Dr. Susan Day. 

13. Soil profile rebuilding is a long-term solution
Spread compost 4 inches deep over the surface of the existing soil.
Use a backhoe to scoop a bucket of soil with compost on the top, lift it several feet in the air, and drop it.
Breaks up compacted soil into large clods
Creates veins of compost down 24 inches
Spread 4-8 inches of topsoil on surface and rototill
Plant trees
Mulch or plant groundcover as desired.
The process was developed by a Virginia Tech research group led by Dr. Susan Day. 

14. Decreases in bulk density persist over time!
Creates veins of compost deep in the soil profile that hold soil channels open for root penetration.
The introduction of organic matter coupled with root activity can create conditions that will lead to formation of soil aggregates over time—leading to long-term soil quality enhancement.
Layman et al Urban Forestry and Urban Greening

15. Which is the best amendment?
Road-side soils have low nutrient availability
Which is the best amendment?

16. Scharenbroch and Watson’s CRUD plots
Compaction and Remediation of Urban Dirt

17. Scharenbroch and Watson’s CRUD plots
Compaction and Remediation of Urban Dirt

18. Nitrogen from fertilizer does not stay in the soil

19. Mulch and compost enhance tree growth most
Scharenbroch and Watson Arboriculture and Urban Forestry

20. Biosolids also enhance tree growth

21. Compost and biosolids are more efficient AND more economical than fertilizer

22. Road-side soils are inundated with salt
Kelsey and Hootman Deicing salt dispersion and effects on vegetation along highways.

23. Salt also reaches sites relatively far from roads
Kelsey and Hootman Deicing salt dispersion and effects on vegetation along highways.

24. Salt collects in white pine foliage
Kelsey and Hootman Deicing salt dispersion and effects on vegetation along highways.

25. Salt enhances water stress (in an already water-limited environment)

26. Salt enhances water stress (in an already water-limited environment)

27. Salt enhances water stress (in an already water-limited environment)

28. Salt enhances water stress (in an already water-limited environment)

29. Ionic stress: Sodium interferes with plant metabolic processes
Na+
Na+
Na+
Na+

30. Gypsum may not be the best solution
Sodium may be bound to water and clay in soil
Calcium in gypsum displaces sodium on clay
Sodium can be leached out
Calcium may also displace hydrogen on clay, increasing pH in an already high pH environment

31. Biochar may be a better solution?
TBD

32. Current best solution is to plant salt-tolerant trees

33. Current best solution is to plant salt-tolerant trees
Prevention!
Current best solution is to plant salt-tolerant trees

34. Right tree, right place
Don’t plant a large tree in a small space
Don’t plant a salt-intolerant tree in the highway median

35. Right amendment, right tree?
Forests with different tree compositions have different organic matter composition and nutrient availability

36. Soil C:N reflects litter C:N
roots
leaves
P < 0.001
P < 0.001
soil
P < 0.001 AM
ECM

37. Maple litters decompose more rapidly than oak littersAM
ECM
Midgley, Brzostek, and Phillips Journal of Ecology

38. Oak-hickory soils have a distinct organic layer
Maple-cherry-tulip poplar soils do not
Oak-hickory soils have a distinct organic layer while maple-poplar soils do not

39. Maple plot: inorganic N economy Oak plot: organic N economy
Low chemical quality litter: high C:N
High chemical quality litter: low C:N
Roots
Roots
Organic N
Organic N
AM fungi
Enzymes
Enzymes
Saprotrophs
ECM fungi
Inorganic N
NH NO3
Inorganic N
NH NO3
Phillips, Brzostek, and Midgley New Phytologist

40. Can we match amendments to trees?
Low C:N
High C:N
Leaf compost
Composted biosolids
biosolids
Wood compost

41. Can we match amendments to trees?
Low C:N
High C:N
Leaf compost
Composted biosolids
biosolids
Wood compost
Sugar maple
Shagbark hickory
Black cherry
Red oak

42. There is no silver bullet
There is no one perfect tree or soil program, because there is no one homogeneous urban environment or site.
Prevention is the best option.