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What is limiting canola yield in southern New South Wales? A diagnosis of causal factors


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Lisson, S, Kirkegaard, JA, Robertson, MJ and Zwart, A 2007 , 'What is limiting canola yield in southern New South Wales? A diagnosis of causal factors' , Australian Journal of Experimental Agriculture, vol. 47, no. 12 , pp. 1435-1445 , doi: 10.1071/EA07041.

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During the 1990s there was considerable evidence from grower surveys and other regional statistics to suggest
that canola (Brassica napus) yields were declining in the medium and high rainfall areas of southern New South Wales
(NSW). A paddock survey was conducted across three regions of southern NSW over three consecutive seasons (2003–05)
to explore the importance of disease and other possible causes of low productivity. Under-performing paddocks were
identified by comparing measured paddock yields with simulated potential yields. The causes of the resultant yield gaps
were identified by analysis of the survey results with growers and consultants and from insights provided by the simulation
analysis. Seasonal water supply and emergence date accounted for around 70% of the variation in yield across the survey,
although no dependence on these variables was evident in 2005 as a result of high spring rainfall. A majority (95) of the
132 paddocks surveyed yielded to within 20% of the simulated potential yield. Disease, while significant in some
paddocks, was limited by the dry seasons, there was no evidence for widespread micronutrient deficiencies and most crops
were adequately supplied with nitrogen. There was no single cause of under-performance and the impact of those causes
varied across regions and seasons. Subsoil constraints (seven paddocks) and late season water stress (six paddocks) were
the most common factors associated with under-performance, while five paddocks had inexplicable yield gaps.
Restrictions to taproot growth were widespread, especially in the southern region where around 60% of paddocks had
significantly restricted taproots in all seasons (>3 on a 0–5 scale). Survey paddocks in which significant root restriction
was found were between 10 and 50% below potential yield. Subsequent soil profile analysis identified a range of possible
subsoil constraints including high soil strength, sodic or saline subsoils or subsurface acidity and further research is
warranted to determine their impact on canola productivity in the region.

Item Type: Article
Authors/Creators:Lisson, S and Kirkegaard, JA and Robertson, MJ and Zwart, A
Journal or Publication Title: Australian Journal of Experimental Agriculture
Publisher: CSIRO Publishing
ISSN: 0816-1089
DOI / ID Number: 10.1071/EA07041
Additional Information:

© CSIRO 2007

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