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
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).
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?)
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.)
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)
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.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