cover crops & soil compaction
DESCRIPTION
Presented to Delaware Vegetable Growers in January 2012TRANSCRIPT
Soil Compaction & Cover Crops
Professor of Soil ScienceDept. of Environmental Science
and Technology.
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…
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• Early spring vegetable crops• Reduced or no-till planting
• Please fill out the survey and • pick up a sample of Tillage™ Radish
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