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Transcript of 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Shipton, 2008 - Unpublished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
Soil aeration and its role for plants – J. Gliński, W. Stępkniewski (1985), CRC Press
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
Soil aeration and its role for plants – J. Gliński, W. Stępkniewski (1985), CRC Press
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
Lower – 1.8 g cm-3
Squares: ■Upper – 1.6 g cm-3
Lower – 1.8 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