Stubble retention in cropping in South East Australia: benefits and challenges. Len Wade
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
Review Terms of Reference <ul><li>What quantitative data exist for SE Australia of yield benefits occurring as a result of retained stubble?? </li></ul><ul><li>What soil benefits may arise as a result of retaining stubble?? </li></ul><ul><li>What yield benefits would we expect to follow from the soil benefits identified?? </li></ul><ul><li>What other problems with stubble retention could suppress possible yield benefits?? </li></ul>
Views <ul><li>“ Conservation Farming” originated to prevent erosion in the USA Great Plains. </li></ul><ul><li>It is a combination of reduced tillage and stubble retention. </li></ul><ul><li>“ Stubble retention” is an essential component of conservation farming. </li></ul><ul><li>“ Yield benefit” was not originally claimed? </li></ul>
Where are we at in central and southern NSW? <ul><li>Growers have largely accepted reduced tillage/direct drilling/no till . </li></ul><ul><li>Growers have continued the practice of late burning of stubble . </li></ul><ul><li>Lag in adopting “conservation tillage” as we still late burn in southern NSW </li></ul><ul><li>Are “the answers known” – just need better extension to fix the problem?? </li></ul>
Drivers of adoption in central and southern NSW? <ul><li>Protection from water erosion? </li></ul><ul><li>Protection from wind erosion? </li></ul><ul><li>Increased moisture storage? </li></ul><ul><li>“ Increased” soil fertility, e.g. soil organic carbon? </li></ul>
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 <ul><li>Protection from water erosion (in the east of the region on sloping ground?) </li></ul><ul><li>Protection from wind erosion (in dry seasons on lighter soils?) </li></ul><ul><li>Increased moisture storage (in seasons with enough stubble?) </li></ul><ul><li>“ Increased” soil fertility, especially soil organic carbon – (small if any?) </li></ul>
Recent local long-term data <ul><li>Condobolin Stubble (1979-1999) </li></ul><ul><ul><li>Mean – 0.14t/ha </li></ul></ul><ul><ul><li>Range –1.21 to 0.56 t/ha </li></ul></ul><ul><li>Wagga Wagga (1979 to 2005) </li></ul><ul><ul><li>Mean – 0.05 t/ha </li></ul></ul><ul><ul><li>Range –1.08 to 0.95 t/ha </li></ul></ul>
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.)
<ul><li>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. </li></ul>Yield Difference (retained-burnt) Vs Growing Season Rainfall (mm)
Conclusions I <ul><li>Stubble blockages, trafficability </li></ul><ul><li>Diseases, including crown rots </li></ul><ul><li>Physical constraints (emergence, soil temperature, solar radiation ) </li></ul><ul><li>Nutrient availability, waterlogging </li></ul><ul><li>Interactions in wetter years </li></ul>
Conclusions II <ul><li>Stubble on the soil surface does improve water infiltration and storage, which is valuable for following crop growth. </li></ul><ul><li>Stubble retention has a negative impact on yield relative to late stubble burning, esp. in years of high growing season rainfall </li></ul><ul><li>The late burn does share some attributes with stubble retention systems, as stubble is at least retained for as long as possible. </li></ul>
Conclusions III <ul><li>Short-term impacts of stubble retention vs stubble burning have not been effectively separated from longer-term impacts </li></ul><ul><li>Some strategic tillage may be essential </li></ul><ul><ul><li>Disease management may require a partial retreat in the direction of cultivate and burn. </li></ul></ul><ul><ul><li>Tillage needed Vs nutrient stratification in no-till </li></ul></ul><ul><ul><li>Lime incorporation needed to remedy acid subsoils </li></ul></ul><ul><li>Smoke pollution from stubble burning may drive change, esp. for human health considerations </li></ul>
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
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