Soil Compaction & Cover Crops

Ray Weilrweil@umd.edu

Professor of Soil ScienceDept. of Environmental Science

and Technology.

Ray Weilrweil@umd.edu

Professor of Soil ScienceDept. of Environmental Science

and Technology.

Com

pact

ion

What is soil compaction?

Polarized light microscope

Compaction from traffic & tillage

AgriCanada

Chiseling

Without restricted

traffic, most field surfaces receive traffic

each year

Without restricted

traffic, most field surfaces receive traffic

each year

Damage to soil structure is worst when soil is wet and organic matter is low!

Lower organic matterHigher water contentWatts, C.W., and A.R. Dexter. 1997. Soil and Tillage Research 42:253-275.

Structural damage sensitivity index

Soil compaction: why the

concern? Physically impedes root growth

Limits water/nutrient uptake from subsoil

Reduces infiltration, drainage drought & ponding

Reduces Oxygen diffusion into soil – yes, roots need to breathe!!

Poor aeration favors fungal root diseases

Reduces fertilizer use efficiency

Increases risk of soil-applied herbicide injury

Physically impedes root growth

Limits water/nutrient uptake from subsoil

Reduces infiltration, drainage drought & ponding

Reduces Oxygen diffusion into soil – yes, roots need to breathe!!

Poor aeration favors fungal root diseases

Reduces fertilizer use efficiency

Increases risk of soil-applied herbicide injury

Crop stress due to impaired root function

Measuringbulk density

Less tillage , less long-term compaction

Soil strength (penetration resistance) measured withCone penetrometer.

http://www.bettersoils.com.au/module6/6_3.htm

< 1 MPa1 - 2 MPa> 2 MPa

CM_0CM_5

CM_10CM_15CM_20CM_25CM_30CM_35CM_40CM_45

So

il D

ep

th

0 1000200030004000500060007000Penetration Resistance, kPa

Hayden Farm, 03/04/03

CM0CM5

CM10CM15CM20CM25CM30CM35CM40CM45

Soi

l Dep

th

Penetration Resistance, kPa

Chestertown02/02 Plow pans and

traffic pans persist, even under no-till.

Plow pans and traffic pans persist, even under no-till.Plow Pan

Plow Pan

-20 70 160 250 340 430 520North ---South, Ft

0

60

120

180

Ea

st_

We

st, F

t

Hayden, kPa at 35 cm

-20 70 160 250 340 430 520North ---South, Ft

0

60

120

180

Ea

st_

We

st, F

tMap of Compaction levels varying within a field.1000 kPa = 145 PSI

Kilo Pascals (kPa) at 35 cm (14 inches) deep

Clay subsoil

Data of Gilker and Weil

Soil water content influence on soil strength

Penetration resistance is meaningful only in context of a certain moisture condition. So don’t let an equipment salesperson test your soil strength in the summer!

High bulk densityLow bulk density

More than Just Cover: Cover Crops as Multiple

Purpose Soil Quality Mgt. Tools

Soil organic matter

Soil organic matter

NematodesNematodes

Food web

Food web

Labile CLabile C

Soil Aggregation

Soil Aggregation

Nitrogen fertility

Nitrogen fertility

Weed suppression

Weed suppression

Nitrogen leaching

Nitrogen leaching

Soil water

Soil water

Cooler soil

Cooler soil

Bio-drilling

Bio-drilling

Cover crops

Cover crops

Crop growth

Crop growth

Bio-drillingBio-

drilling

Rye effect on topsoil bulk density (g/cm3) in Spring Rye effect on topsoil bulk density (g/cm3) in Spring

Data and photo from Sjoerd Duiker - PSU

With Rye w/o Rye

Both samples under manure spreader tracks on dairy farm operation

b

a

ab

ab

1.35

1.55

1.6

1.65

w/o Rye with Rye

Rye killed May 1

Rye killed May 15

1.35

1.4

1.45

1.5

1.55

1.6

1.65

w/o Rye with Rye

b

1.4

1.45

1.50-4” deptha a a

4-8”depth

Rye roots in a compacted soil

Not very good at soil penetration

Key differences are in the roots!

Forage radish

Forage radishRye

Rape

Forage radish: • kills itself• suppresses winter weeds

“Weil’s Law” of root/shoot ratio effects

1. If conditions above ground are limiting, the roots will suffer most.

2. If conditions below ground are limiting, the shoots will suffer most.

e.g. N deficiency or drought (soil limit) increases root/shoot ratio

e.g. late planting or crowding (above ground limit) decreases root/shoot ratio.

+N -N

1 2 3 4 5Seeding date (weeks after August 20)

0

1000

2000

3000

4000

5000D

ry m

atter

( shoot or

fleshy r

oot)

, kg/h

a

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Root/s

hoot ra

tio

Shoot

Root

Root/shoot ratio

Means of four sites

Effect of seeding date on forage radish root & shoot growth in fall

(measured Dec. 1)

Larger diameter roots have greater ability to penetrate compacted soil

1.14

1.25

1.32

1.16

1.57

1.43

Bulk densities (Mg/m3)

uncompacted compacted

Data from: Materechera, S, M. Alston, J Kirby, and A.Dexter. 1992. Plant and Soil 144:297-303.

10

20

0

Which answer to

compaction?

Ripper Radish

“Radish – Ripper”

Steve Groff

But – how to learn what the roots are doing down in the subsoil?

Changes in Soil Water Tension at 50 cm (20 inch) depth during summer as affected by preceding fall cover crop.

Wet

Dry

June July August

One approach: monitor crop use of water from the subsoil

Subsoil 17 in (42 cm) deepGroff farm – clay loam

Subsoil 16 in (40 cm) deepWye, Md – silty clay loam

Investigating roots with fiber optic camera: minirhizotron

First published proof of “bio-drilling” to alleviate subsoil compaction

Rapeseed root

Williams and Weil (2004)

• No: no pass• Medium: one pass• Heavy: two passes

• No: no pass• Medium: one pass• Heavy: two passes

3 compaction levels:3 compaction levels:

For each pass Wt: 1.19*104 kgcontact area: 1600 cm2 force: 7.44*104 N

For each pass Wt: 1.19*104 kgcontact area: 1600 cm2 force: 7.44*104 N

Compaction Experiment (Don’t try this on your farm!)

Rye and Radish Cover Crops in Dec. after compaction

Forage Radish roots under no or heavy compaction

Note: the whole experimental site was disked to 8 cm (3 inches) to provide a suitable seedbed before planting cover crops.

Core-break method to determine at root numbers with depth.

Taking soil core to a depth of 60 cm Counting root numbers at the breakage faces

Three cores per plot

Learning about roots the hard way – digging them up and counting them!

Differences of root numbers (per 32 cm2) at each depth are indicated by *; student t-test, a=0.05

Root penetration capability of 3 cover crop growing under heavy compaction Root penetration capability of 3 cover

crop growing under heavy compaction

Roots under high compaction

0

10

20

30

40

50

0 10 20 30 40 50 60 70Roots

FR

rape

Rye

* ***

**

*** *

**

*

FR had 2 to 4 times as many subsoil roots as

rye or rape

Roots per 32 cm2

So

il d

epth

, cm

So

il d

epth

, cm

Chen and Weil, 2010

45 cm2

Chen and Weil, unpublished

Roots of corn following rye, radish or no

winter cover crop

Roots of corn following rye, radish or no

winter cover crop

Late July

Plow depth

Managing soils to improve plants

plants soils

Stick around for the Q and A Panel!

Stick around for the Q and A Panel!

Think about…

We want to work with you!

If you are interested in using cover crops for….

• Early spring vegetable crops• Reduced or no-till planting

• Please fill out the survey and • pick up a sample of Tillage™ Radish

seed