Impacts of retained wheat stubble on canola in southern New South Wales
S. E. Bruce A B C , J. A. Kirkegaard A , J. E. Pratley B and G. N. Howe AA CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia.
B Charles Sturt University, Wagga Wagga, NSW 2678, Australia.
C Present address: CSIRO Sustainable Ecosystems, GPO Box 284, Canberra, ACT 2601, Australia. Corresponding author: Email: sarah.bruce@csiro.au
Australian Journal of Experimental Agriculture 45(4) 421-433 https://doi.org/10.1071/EA04133
Submitted: 13 July 2004 Accepted: 4 November 2004 Published: 23 May 2005
Abstract
Field experiments were conducted in southern New South Wales to determine the effect of surface-retained wheat stubble on the emergence, growth and yield of canola. The 5 experiments included treatments to investigate the impact of stubble load, stubble cultivar and level of decomposition as well as the impact of different environments on the crop response. Overall, 5 t/ha of surface-retained wheat stubble reduced the rate of emergence, plant establishment (mean reduction 33%), vegetative biomass (–56%) and yield (–23%), although the impact varied with site and season. Laboratory experiments assessing the phytoxicity of stubble revealed the possible role of allelopathy in the growth response at 1 site; however, there was no correlation between laboratory phytotoxicity of different stubble cultivars and their impact on canola growth at any other site. Wheat stubble comprising thinner stems (lower straw linear density) had a greater impact on emergence at 2 of the sites, indicating a possible role of reduced light penetration in the growth response. Colder temperatures on the surface of the stubble also reduced emergence and growth, and caused seedling death at the coldest sites. The experiments confirm the widely observed phenomenon of poor canola growth in surface-retained wheat stubble, and suggest several possible mechanisms for the effect, although further studies are required to determine their relative importance in different environments.
Additional keywords: stubble retention, canola, hypocotyl, direct drilling, phytotoxicity, allelopathy, phytotoxins, allelochemicals, leachates.
Acknowledgments
We thank Sara Hely for technical support and staff at the CSIRO Ginninderra Experiment Station for assistance with the field experiments. Mr Peter Holding, Mr Bernard Hart and Mr Murray Long kindly provided land for the experiments. Warren Müller from CSIRO Maths and Information Sciences provided statistical advice. Funding from GRDC is gratefully acknowledged.
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