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Stubble retention in cropping in South East Australia: benefits and challenges. Len Wade
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Stubble retention in cropping in South East Australia: benefits and challenges. Len Wade


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A presentation from the WCCA 2011 event held in Brisbane, Australia.

A presentation from the WCCA 2011 event held in Brisbane, Australia.

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  • 1. Stubble Retention in Cropping in South-East Australia: Benefits and Challenges Professor Len Wade, Charles Sturt University, Locked Bag 588, Wagga Wagga NSW 2678 5 th World Congress on Conservation Agriculture and 3 rd Farming Systems Design Conference Brisbane, 27 September 2011
  • 2. 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??
    • “ 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?
  • 4. 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??
  • 5. Adoption in NSW (ABS 2001)
  • 6. Estimated stubble loads at sowing
  • 7. 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?
  • 8. 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).
  • 9. 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
  • 10. 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?)
  • 11.  
  • 12. 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
  • 13. 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.)
  • 14.
    • 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.
    Yield Difference (retained-burnt) Vs Growing Season Rainfall (mm)
  • 15. Conclusions I
    • Stubble blockages, trafficability
    • Diseases, including crown rots
    • Physical constraints (emergence, soil temperature, solar radiation )
    • Nutrient availability, waterlogging
    • Interactions in wetter years
  • 16. 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.
  • 17. 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
  • 18. ACKNOWLEDGEMENTS/REFERENCES Peter Cornish (1987). Effects of wheat residues and tillage on the water balance of a red earth soil. 4 th Australian Agronomy Conference, La Trobe. 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).