Professor Len Wade discusses the benefits and challenges of stubble retention in cropping systems in South-East Australia. He finds that stubble retention can improve soil moisture storage and potentially increase soil organic carbon in the long-term. However, yield benefits of stubble retention compared to stubble burning are mixed and depend on growing season rainfall. In wet years, stubble retention may decrease yields due to issues like disease, slugs, and soil compaction. Strategic tillage or burning may still be necessary to manage these challenges.

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

5. Adoption in NSW (ABS 2001)

6. Estimated stubble loads at sowing

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

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.)

18. g.au 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. 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