Soil Quality - University of Hawaii

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

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