measuring oxygen diffusion through cricket pitch...

Measuring oxygen diffusionthrough cricket pitch soils

Simon [email protected]

With:Dr I.T. James,Dr M.D. Bartlett

Outline

• Introduction

• Why do we need to aerate cricket pitches?

• What is aeration?

• Conceptual model

• Experimental results

Title picture courtesy of: JessicaHarper.com

Why do we need toaerate cricketpitches?

• A cricket square is a deliberately compacted soil butwhere efficient rooting is necessary

• Highly compacted soil is required in order to achievethe correct mechanical parameters for ‘good’ ball-surface interactions

• Compaction reduces pore size and connectivity

1.6 Mg m-3

Soil bulk density vs.porosity

1.2 Mg m-3

5 mm

Harris et al. 2003, FEMS Microb. Ecol. 44, 45-56

PORE MAPS FROM SOIL THIN SECTIONS

Why do we need toaerate?

This results in:

• poor gas exchange between the soiland atmosphere, particularly withincreasing depth

• reduced hydraulic conductivity

• reduced infiltration

www.ryanlawn.com/resource/aeration.jpg 28/05/2008

What does aerationdo?

Aeration treatments create macropores

Four principal methods:

• Spiking

• Drilling

• Blasting

• Slicing

www.wynnslawncare.com/.../core_aeration_pic1.gif 20/04/2010

Mechanical barrier orhypoxia?

• Density did not effectrootmass with depth

• Open to air at both ends

Dep

thm

m

Shipton, 2008 - Unpublished

Interactions between soilparameters influencing soiloxygenation status

Soil Conditions

Structure Moisture Respiration

Eo,

Total porosity

Θ, Water filled porosity

q,Soil respiration

Eg,gas filled porosity

d, effective thicknessof water film around root

D, coefficientof macrodiffusion

De, effectivediffusion coefficient

Oxygendiffusion rate

C(x),

O2 concentrationwith depth

Lan,Oxygenation depth

Plant growth Redox processes

Soil aeration and its role for plants – J. Gliński, W. Stępkniewski (1985), CRC Press

1D diffusion model

• Based on a 1D model of O2 concentration in the soilprofile

• The model is linked to each individual soil type by soilwater characteristics

• Soil is broken down into layers; factors affecting O2

concentration are constant within each layer

Layered soil profile

Layered breakdown of soil profile


Di – Diffusion coefficient of layer i

qi – Respiratory quotient of layer i

Hi – Lower boundary of layer i

CHi – Concentration of O2 at Hi

ai – Size of layer I

z – Depth

1HC

2HC

3HC

0C00 z

1H

2H

3H

1a

2a

3a

1q

2q

1D

3q

2D

3D

Depth Concentration

Diffusion constant

• Uses soil water characteristics of a soil to calculatediffusion constant

• Links model to specific soil types

b

D

D3

2

100

1003100

0

04.02

D0 – Diffusion coefficient of oxygen in airε100 – Air filled porosity at a soil water potential of -1 m H2Oε – Air filled porosity for any given Db – Campbell soil water retention parameter (after Campbell, 1974)

Campbell, G.S. 1974. A simple method for determining unsaturated conductivity from moisture retention data. Soil Sci. 117:311-314Moldrup, P. et al. 2000. Predicting the gas diffusion coefficient in undisturbed soil from soil water characteristics.Soil Sci. Soc. Am. J. 64:94-100

-1.0 -0.8 -0.6 -0.4 0.0S

oil

wate

rsuction

(Log

m)

0

2

3

4

5

-1.0 -0.8 -0.6 -0.4 0.0

So

ilw

ate

rsuctio

n(L

og

m)

0

2

3

4

5

b = 9.09; r² = 0.98b = 9.91; r² = 0.96

b = 9.53; r² = 0.97b = 10.2; r² = 0.99

i) ii)

b = 9.85; r² = 0.99b = 7.84; r² = 0.97

b = 13.3; r² = 0.98b = 5.48; r² = 0.99

Air filled porosity (Log Air filled porosity (Log

Shipton, unpublished

Linear regression of soil water potential and air filled porosity to determinethe Campbell water retention parameter, given as the gradient of the line

1.2 Mg m-3 (●), 1.4 Mg m-3 (□), 1.6 Mg m-3 (▲), 1.8 Mg m-3 (○)

Soil 1 Soil 2

k

kkk

n

kiii

kD

HzqHzaq

HCzC2

2

)(

2

11

1

Concentration of O2 atdepth, z

Key factors include:

• Soil bulk density

• Soil moisture content

• Respiratory quotient


Simulations

• Two soils were used in the simulations

• Both soils are representative of those used in moderncricket pitches

• Two simulations were run for each soil type

Simulation A

Simulation A:

• Bulk density constant

• qi was different foreach layer

00 z

1H

2H

3H

1a

2a

3a

1q

2q

1D

3q

2D

3D

Depth

1.2 g cm-3

1.6 g cm-3

1.4 g cm-3

1.8 g cm-3

● Soil 1

○ Soil 2

Simulation A

• General trend of decreased O2 concentration at depthwith increasing bulk density

• Bulk density of less than 1.4 g cm-3 not likely to be amanagement problem

• Rapid diminishment in O2 with depth at 1.8 g cm-3

• Likely to lead to shallow rooting

Simulation B

Simulation B:

• Bulk density of layer:1 < 2 ≤ 3

• Layer 3 = 1.8 g cm-3

• qi was different foreach layer

00 z

1H

2H

3H

1a

2a

3a

1q

2q

1D

3q

2D

3D

Depth

Simulation B

Circles: ●Upper – 1.4 g cm-3

Lower – 1.6 g cm-3

Triangles: ▼Upper – 1.4 g cm-3


Squares: ■Upper – 1.6 g cm-3


Simulation B

• General trend of rapid diminishment of O2 below thecompacted layer

• Compacted layer represents not only a mechanicalbarrier to root growth but also a respiratory limitation

Model Conclusions

• Model implies a mechanism whereby decreases inroot depth with increasing bulk density are related todiminishing availability of O2

• Trends highlighted indicate the importance ofsufficiently penetrating aeration techniques

• Current practise recommends aeration for potentiallythe wrong reasons

Model limitations &assumption

• Averaging assumptions over the 200 mm layers

• Diffusion is the only method of gas exchange

• One-dimensional gas movement

• Based on Fick’s law

• Limitations for describing gas movement inporous media

Real-time diffusionthrough soil

• 35 cm of compacted soil

• 4 gas wells at specific depths

• Purge soil with nitrogen thenmonitor the influx of oxygenfrom the atmosphere

Real-time diffusionthrough soil

Atmospheric air 20.86%

Measuring pitch gasses

Soil atmosphere atCranfield Day 1: weather was fine and dry

Day 2: weather was raining and wet

Conclusions

• Density is not itself a limiting factor to root growth

• Oxygen diffusion through compacted soils is slow

• Aeration may need to be more targeted towardsimproving gas exchange and hydraulic conductivity

Measuring oxygen diffusionthrough cricket pitch soils

Simon [email protected]

With:Dr I.T. James,Dr M.D. Bartlett

measuring oxygen diffusion through cricket pitch...

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