removal of a subsoil constraint. when does it pay? imma farre, bill bowden, stephen davies &...
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Removal of a subsoil constraint.
When does it pay?
Imma Farre, Bill Bowden, Stephen Davies & Dennis van Gool
Department of Agriculture and Food Western Australia
Outline
The issue
Aims of the work
Methodology
Results
Conclusions
Take home message
Introduction
- Subsoil constraints lead to a reduction in root growth, which results in reduced yield.
- Constraint removal can have positive or negative effects on yield, depending on season, location, soil type and constraint level.
- Simulation modelling can be used to give an indication of the level of risk associated with removal of subsoil constraints.
- Aim: to assess the impact of soil type, location, season and severity of the constraint on the yield response of wheat to removal of a non-specific subsoil constraint.
Methods
APSIM-Wheat simulations
Loc: 30 locations in WA
Soil types: loamy duplex (heavy)loamy sand (light)
Years: 1957-2006
Constrained root growth at 20-40 cm depth:(non-specific constraint)
unconstrainedtypical severeextreme
Loamy Duplex
0
50
100
150
200
250
300
0 0.1 0.2 0.3 0.4Volumetric Water Content (%)
De
pth
(cm
)
ll15
dul
Loamy Sand
0
50
100
150
200
250
300
0 0.1 0.2 0.3 0.4Volumetric Water Content (%)
De
pth
(cm
)
ll15
dul
Results. Root depth (cm)
mean rooting depth, 1957-2006
level of constraint
Location Soil type none typical severe extreme
Mingenew
Loamy duplex 102 95 70 23
Mingenew Loamy sand 184 170 97 24
The different levels of subsoil constraints caused a reduction in final root depth (cm)
0
500
1000
1500
2000
2500
0 50 100 150 200
DAS
Ro
ot d
ep
th(m
m)
Mingenew, loamy sand, 1999
Yield response to removal of constraints
Yield response to removal of constraints
Assuming amelioration cost $40/ha and return $250/t grain
Return to amelioration
Average yield response to constraint removal
Loamy duplexTypical
Loamy sandTypical
Frequency of positive responses to constraint removal
Loamy duplexTypical
Loamy sandTypical
Loamy duplexTypical
Loamy sandTypical
Loamy duplexSevere
Loamy sandSevere
Conclusions
Wheat yield response to constraint removal is on average positive, but
can be negative.
The information on probability of positive response becomes important
in decision making.
Factors that have the major impact on the size and frequency of the
response:
1. Soil type
2. Severity of the constraint
3. Season
Conclusions
In summary for this study the following factors are associated with positive, variable or negative responses to constraint removal:
Likelihood of response
Positive Variable or Negative
Constraint is severe or extreme (Root depth < 30 cm)
Mild or typical constraints
Higher rainfall locations Low rainfall locations
Wetter seasons Drier seasons
Light soils(Deep roots are critical to access a available
water)
Heavy soils (more plant available water in top soil layers)
Take home message
Greater benefit if:
Severe and extreme constraintsTypical constraints & High yielding locations & Wet seasonsLight soils
Greater risk if:
Mild constraints & Low yielding locations & Dry seasons & Heavy soils
Thanks
Paper available - Hard copies - email: [email protected] - Online Proceedings of the Australian Agronomy
Conference 2010