Stubble Retention in Cropping in South-East Australia:

Benefits and Challenges

Professor Len Wade, Charles Sturt University, Locked Bag 588, Wagga Wagga NSW 2678

5th World Congress on Conservation Agricultureand 3rd Farming Systems Design Conference

Brisbane, 27 September 2011

Review Terms of Reference

• What quantitative data exist for SE Australia of yield benefits occurring as a result of retained stubble??

• What soil benefits may arise as a result of retaining stubble??

• What yield benefits would we expect to follow from the soil benefits identified??

• What other problems with stubble retention could suppress possible yield benefits??

Views

• “Conservation Farming” originated to prevent erosion in the USA Great Plains.

• It is a combination of reduced tillage and stubble retention.

• “Stubble retention” is an essential component of conservation farming.

• “Yield benefit” was not originally claimed?

Where are we at in central and southern NSW?

• Growers have largely accepted reduced tillage/direct drilling/no till.

• Growers have continued the practice of late burning of stubble.

• Lag in adopting “conservation tillage” as we still late burn in southern NSW

• Are “the answers known” – just need better extension to fix the problem??

Adoption in NSW (ABS 2001)

(b)

Stubble management method

Baled/grazed Ploughed Mulched Intact Other Burnt

Fre

quen

cy (

%)

0

10

20

30

40

50

60

Northern NSW Central NSW Southern NSW

Estimated stubble loads at sowing

Estimated stubble at sowing (nearest t/ha)

0 1 2 3 4 5 6 7

Fre

quen

cy (

% o

f yea

rs)

0

10

20

30

40

50

60

70

Merredin (Jarvis 1987)Wongan Hills (Jarvis 1987)Condobolin (Fettell pers comm)Wagga Wagga (Heenan et al and MC pers)

Drivers of adoption in central and southern NSW?

• Protection from water erosion?

• Protection from wind erosion?

• Increased moisture storage?

• “Increased” soil fertility, e.g. soil organic carbon?

Soil moisture storage at Wagga Wagga NSW in May 1985 under a range of stubble loads following 140 mm of rain, and 35 mm of

additional irrigation (Cornish 1987; Cornish and Lymbery 1986).

Stubble rate (t/ha)

0 2 4 6 8 10 12 14 16

Wat

er

sto

red

(m

m)

0

10

20

30

40

50

60

70

80

Average linear slope of soil organic C in the surface (0-10cm) over 21 years at a site at Wagga Wagga, NSW (after

Heenan et al. 2004).

        Soil organic C

Rotationa Stubble management

Tillageb Average slope (kg C/ha.yr)

T valuec

1 L/W Retained DD −8 NS

2 L/W Retained CC −199 ***

3 L/W Burnt DD −138 **

4 L/W Burnt CC −284 ***

5 W/W Burnt CC −389 ***

6 W/W(+N) Burnt CC −311 ***

7 S(grazed)/W Retained CC −72 NS

8 S(mulched)/W Retained DD 185 ***

9 S(mulched)/W Retained CC −4 NS

a L = lupins; W = wheat; S = subterranean clover

bDD = direct drilled; CC = three pass tillage

c significance of t value; NS, not significant; **, P 0.01; ***, P 0.001

Drivers of adoption in central and southern NSW

• Protection from water erosion (in the east of the region on sloping ground?)

• Protection from wind erosion (in dry seasons on lighter soils?)

• Increased moisture storage (in seasons with enough stubble?)

• “Increased” soil fertility, especially soil organic carbon – (small if any?)

Recent local long-term data

• Condobolin Stubble (1979-1999)– Mean – 0.14t/ha– Range –1.21 to 0.56 t/ha

• Wagga Wagga (1979 to 2005)– Mean – 0.05 t/ha– Range –1.08 to 0.95 t/ha

Relationship between growing season rainfall and the difference in grain yield between stubble retention and stubble burning (yield stubble retained-yield stubble

burnt) under direct drill sowing in a long term experiment (1979-1999) at Condobolin, New South Wales. Data point in red are years of no harvestable yield due to drought,

and those in blue are post drought years (see Fettell and Gill 1995; NA Fettell pers comm.)

Growing season rainfall (May- Oct; mm)

0 100 200 300 400 500Yie

ld d

iffe

ren

ce (

dd

re

tain

ed

- d

db

urn

t; k

g/h

a)

-1400

-1200

-1000

-800

-600

-400

-200

0

200

400

600

800

1979

198519861987

1988

1989

1990

1991

1992

1993

19961997

1998

1999

198019821994

(1981)

(1983)

(1995)

Ydiff = 1097 - 5.73.rainVAF = 73.7%

Relationship between rainfall parameters (GS, growing season, May-Oct; spring; winter) and mean difference in yield between stubble-retained and stubble-burnt/removed wheat crops in two long-term experiments (Billa Billa and Wagga Wagga; from Kirkegaard 1995). A fitted line (grey, broken) to the Wagga Wagga (GS) is shown – Reproduced from Fig. 27 of Scott et al 2010.

Rainfall (mm)

0 100 200 300 400

Me

an

yie

ld d

iffe

ren

ce

(t/

ha

)

-1.5

-1.0

-0.5

0.0

0.5

1.0Billa Billa (winter)Wagga Wagga (spring)Wagga Wagga (GS)

Wagga Wagga (GS; suggested fit)

Yield Difference (retained-burnt) Vs Growing Season Rainfall (mm)

Conclusions I

• Stubble blockages, trafficability

• Diseases, including crown rots

• Physical constraints (emergence, soil temperature, solar radiation)

• Nutrient availability, waterlogging

• Interactions in wetter years

Conclusions II

• Stubble on the soil surface does improve water infiltration and storage, which is valuable for following crop growth.

• Stubble retention has a negative impact on yield relative to late stubble burning, esp. in years of high growing season rainfall

• The late burn does share some attributes with stubble retention systems, as stubble is at least retained for as long as possible.

Conclusions III• Short-term impacts of stubble retention vs

stubble burning have not been effectively separated from longer-term impacts

• Some strategic tillage may be essential– Disease management may require a partial retreat in

the direction of cultivate and burn.– Tillage needed Vs nutrient stratification in no-till– Lime incorporation needed to remedy acid subsoils

• Smoke pollution from stubble burning may drive change, esp. for human health considerations

g.auACKNOWLEDGEMENTS/REFERENCES

Peter Cornish (1987). Effects of wheat residues and tillage on the water balance of a red earth soil. 4th Australian Agronomy Conference, La Trobe. www.agronomy.org.au

John Kirkegaard (1995). A review of trends in wheat yield responses to conservation cropping in Australia. Australian Journal of Experimental Agriculture 35, 835-848.

Brendan Scott, Phil Eberbach, Jeff Evans, Len Wade (2010). Stubble retention in cropping in southern Australia: Benefits and challenges. Graham Centre Monograph No.1. (105 p). www.csu.edu.au/research/grahamcentre