removal of a subsoil constraint. when does it pay? imma farre, bill bowden, stephen davies &...

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: imma.farre@agric.wa.gov.au - Online Proceedings of the Australian Agronomy

Conference 2010