Root Development in Soils. Root Growth Hypothesis—Minimum Effort.

Root Development in Soils

Root Growth Hypothesis—Minimum Effort

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

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

Characterizing undisturbed soil

• Shottower Silt Loam

Applying Compost: Profile Rebuilding

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

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)

• 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

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

Bur Oak and Elm Canopy after 3 yrs

Soil Treatment

PR UN ME ET

Ca

no

py

m2

0

5

10

15

20

25

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

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?

Partial support provided by the Tree Research & Education Fund