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Soil Quality
What is it?How do we measure it?How do we enhance it?
5 Functions
of Soil
Medium forPlant growth
Recyclingsystem
Habitat forSoil organismsWater supply
and purification
Engineering Medium
DefinitionThe capacity of a soil to:1. Sustain biological productivity and
diversity2. Maintain environmental quality3. Promote plant and animal health
Source:Doran & Parkin, 1994)
J.L. Deenik J.L. Deenik
Brady & Weil, 2004
Good vs Bad
Soil Quality Assessment
• Look• Feel• Smell• Other ?
• Physical• Chemical• Biological
Descriptive Analytical
J.L. DeenikJ.L. Deenik
Soil Quality AssessmentIndicator Rationale
PhysicalTexture Retention and transport of water and chemicalsDepth of soil and rooting Estimate of productivity potential and erosionBulk density and infiltration Potential for leaching, productivity, and erosionWHC Water retention, transport, and erosivity
ChemicalTotal SOM C sequestration, potential fertility, and stabilityActive OM Structural stability and food for microbespH Biological and chemical activity threshholdsEC Plant and microbial activity threshholdsExtractable NPK Plant available nutrients, potential for environmental contamination
BiologicalMicrobial biomass Early warning of management effect on organic matterMineralizable N Soil productivity and N supply potentialSpecific respiration Microbial activity per unit microbial biomassMacroorganisms Potential influenceDoran & Parkin, 1994
Indicators’ Sensitivity to Management
• Water content• Respiration• Bulk density• pH• NPK
• Aggregation• Microbial
biomass• Active C• OM content
• Soil depth• Slope• Climate• Restrictive
layers• Texture• Mineralogy
Rapid Intermediate Permanent
• pH and EC• Bulk density• Depth of soil• Texture• WHC• Extractable NPK
• Total SOM• Active OM• N mineralization• Microbial biomass• Microbial diversity
Relatively Simple Difficult
Soil Quality Monitoring
• Intensive sampling• Expensive analysis• Field test kits?
http://www.bentonswcd.org/store/
Measuring Soil Responses to Management
• Sustainable Management• Stability in production and profitability• Protection and enhancement of the natural
resource base• Soil responds to
management• Assessment Approaches
J.L. Deenik
Cultivation and Soil Organic MatterS
oil O
rgan
ic M
atte
r (m
g/ha
)
Time After Start of Cultivation (years) Brady & Weil, 2004
Effects Due to Loss of SOM• Increased bulk density• Decreased soil tilth
– Poor soil structure • Decreased water infiltration
– Increased erosion• Decreased water holding capacity
– Increased susceptibility to drought• Decreased N mineralization potential• Decreased microbial biomass/activity• Decreased macrofauna
Management Effects on Soil Quality
Brady & Weil, 2004
Management Effects on Soil Quality
Management Effects on Soil QualityExamples from Hawaii
Tota
l N (%
)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Soi
l Org
anic
C (%
)
0
2
4
6
8
10
12
Soi
l pH
0
1
2
3
4
5
6
7UncultivatedCultivated
Ext
ract
able
P (p
pm)
0
100
200
300
400
500
600
700
Waimea soil:
Management Effects on Soil QualityExamples from Hawaii
Waimea soil:
Agg
rega
te S
tabi
lity
(5)
0
20
40
60
80
100
120
MB
C (p
pm)
0
200
400
600
800
1000
1200UncultivatedCultivated
HW
EC (p
pm)
0
500
1000
1500
2000
2500
N M
iner
aliz
atio
n Po
tent
ial (
ppm
)
0
20
40
60
80
100
120
140
160
180
Management Effects on Soil QualityExamples from Hawaii
HydrudandUstand Ustoll Perox Ustox
HW
EC
(mg
C k
g-1)
0
500
1000
1500
2000
2500
3000
3500
UncultivatedConventional Cultivation
HydrudandUstand Ustoll Perox Ustox
MB
C (m
g C
kg-1
)
0
500
1000
1500
2000
2500
3000
Hot H2O Extractable C Microbial Biomass C
Management Effects on Soil QualityExamples from Hawaii
N Mineralization Potential Aggregate Stability
Hydrudand Ustand Ustoll Ustox
N M
iner
aliz
atio
n P
oten
tial (
mg
N k
g-1)
0
50
100
150
200
250
300
Soil Suborder
Hydrudand Ustand Ustoll Perox
Agg
rega
te S
tabi
lity
(%)
0
20
40
60
80
100
120
UncultivatedConventional Cultivation
Management Effects on Soil QualityExamples from Hawaii
Compost ExperimentEffects of compost on Radish growth and N mineralization
0 11.2 44.8
Fres
h W
eigh
t (g/
plan
t)
0
10
20
30
40
50
60
70
% In
fect
ion
0
10
20
30
40
50
60
70
Fresh Weight % Infection
Compost Addition Rate (T/ha)
0 11.2 44.8
Mar
keta
ble
Yiel
d (g
/pla
nt)
0
10
20
30
40
50
0 11.2 44.8
N M
iner
aliz
atio
n P
oten
tial (
mg
NH
4+ -N k
g-1
-10
-5
0
5
10
15
20
25
a b c
Compost added at 10 and 40 T/acre
Management Effects on Soil QualityExamples from Hawaii
Effects of organic management on a Vertisol, Waianae
MB
C (m
g C
kg-1
)
0
200
400
600
800
1000
1200
1400
1600
HW
EC
(mg
C k
g-1)
0
500
1000
1500
2000
Agg
rega
te S
tabi
lity
(%)
0
10
20
30
40
50
60UncultivatedOrganic Management
• Cultivation has had a negative effect on soil quality.• Clear evidence that changes in SOM management are
required to improve soil quality.• Does improving soil quality directly improve crop
production?
Fundamental Questions
• Does improving soil quality parameters improve crop quality and production?
• Do the benefits of using green manure rotations outweigh the additional cost and labor?
• Are animal manures a viable option?
• What role does research play in helping farmers enhance soil quality
J.L. Deenik
Building Partnerships
Solution