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Root Development in Soils
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Root Growth Hypothesis—Minimum Effort
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Root Growth Hypothesis—Profile Rebuilding
• Measure depth and root length density in situ• Frequent measurement can reveal root birth and
death patterns (root turnover)• Soil genesis
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Four TreatmentsUndisturbed
Minimum Effort (a.k.a. Builder’s
Special)
Enhanced Topsoil
Profile Rebuilding
4 in (10 cm) topsoil
4 in (10 cm) topsoil, interface scuffed by tilling
Includes compost, subsoiling, and topsoil
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Characterizing undisturbed soil
• Shottower Silt Loam
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Applying Compost: Profile Rebuilding
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Preparing the plots: Pre TreatmentVegetation and topsoil scraped and stockpiled
8 passes with a compactor at
optimal moisture for compaction.
Bulk density = 2.0 g/cm3
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Tilling: “Enhanced Topsoil” and “Profile Rebuilding”For the ET and PR treatments, the topsoil was rototilled to a depth of 8 inches (20 cm).
ET: to disrupt interface
PR: to prepare planting surface (eliminate clods)
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• Similar to technique suggested by Kaj Rolf, Swedish researcher
• Can be used in confined spaces (median strips, parking lot islands)
• Addresses subsoil compaction
Subsoiling Technique Step 1: Apply 4 inches leaf litter compost
Step 2: Use backhoe to go down 2 feet, scoop, and allow to fall down to break up clods. Large clods may require a prod with the backhoe. Creates veins of compost deep in profile.
Step 3: Apply 4 inches reserved topsoil
Step 4: Rototill to 8 inch depth
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Soil Preparation Affects Growth in First Year
Burr Oak Elm First Lady Flowering
Cherry
Red Maple Swamp White Oak
0
100
200
300
400
500
600
700
Enhanced Topsoil
Minimum Effort
Profile Rebuilding
Undisturbed -Check
Aver
age
cros
s-se
ction
al tr
unk
area
incr
ease
dur
ing
year
on
e m
m2
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Bur Oak and Elm Canopy after 3 yrs
Soil Treatment
PR UN ME ET
Ca
no
py
m2
0
5
10
15
20
25
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Profile Rebuilding
• Short termAids in establishment
• We will be able to quantify how much canopy you get for your investment
• To be determined in the long term– Soil biogenesis– Carbon storage– Root production and depth– Soil water capture
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Questions to Pose
• Can we improve soil function for stormwater throughout a city?
• Can trees roots improve drainage from bioretention areas and make underdrainage unnecessary?
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Partial support provided by the Tree Research & Education Fund