Improving the performance of canola

Transcription

1 The challenge - Keeping canola in the rotation Description Authors Collaborators Research Update - Southern Region (High Rainfall) - July 2004 John Kirkegaard, Susie Sprague CSIRO Plant Industry, Canberra Ph: , john.kirkegaard@csiro.au Peter Hamblin, Agritech Crop Research, Young NSW Best Bet Canola Project, (Grain Growers Association) C/- Harden District Rural Advisory Service FarmLink Canola Plus (GRDC) C/- Kirrily Condon, FarmLink, Temora Presented Chris Duff, Chandlers Landmark, Monteagle, chris.duff@landmark.com.au Orange, NSW Why keep canola in the rotation? The disease-break benefits of canola have underpinned the most rapid improvements in wheat yields in Australian history Wheat after canola yields on average 20% more than after wheat, and benefits can be measured in crops 2-3 years later Much of the economic benefit of canola derives from improvements in the following wheat crop rather than the canola itself If canola prices or yields are low, growing wheat on wheat can be profitable if risk factors are minimised. Improving the performance of canola Canola yields have been static or declining in southern NSW in recent years. The diseases Blackleg and Sclerotinia are key factors - when controlled or absent canola yields to its water-limited potential Blackleg can be controlled using varieties with good disease resistance,

2 isolation from last year's canola stubble (>500m) and seed or fertiliser fungicides in high risk situations. The management decisions come down to potential risk and cost The choice for Sclerotinia control is not as straight-forward - the disease is weather dependant and the correct spray timing is not black and white. Guidelines for economic control need refining Don't forget the basics - sowing time, soil ph, and careful attention to nutrition Canola will not grow well in retained wheat stubble (> 3 t/ha) spread across the sown rows. If necessary, canola can be established in wheat stubble successfully using sowing techniques to push stubble onto the inter-row (wider rows, narrow points and press-wheels and no covering devices). The challenge for canola The recent phenomenon of static or declining yields of canola in southern NSW has put some pressure on growers to consider reducing the area sown and increase the amount of back to back wheat crops. This has been exacerbated by a series of drier seasons in which cereals often outperform canola. It is worth re-considering the previous data indicating the magnitude of the expected benefits from canola in the system, while at the same time identifying and addressing the major causes for the declining canola yields. Canola impacts on wheat A compilation of 26 experiments involving Brassica break crops from 1988 to 1998 indicated that on average, wheat after brassicas yielded 20% more than wheat after wheat, although yield responses varied from a 104% yield increase to a 12% yield decrease. The two-year gross margin was 25% higher for canola-wheat than wheatwheat, and much of this benefit derived from improvements in the following wheat crop rather than the canola itself. The wheat failed to respond to a previous canola crop in only three of these 26 experiments, due to a dry finish or drought (1991 and 1994), inadequate N application or where initial disease levels were low. Although there have been some reports of poor wheat growth following canola, a recent survey suggests the problem is not widespread and can be readily controlled with attention to nutrition, herbicide and stubble management. The improved yield of following wheat crops was also associated with increased water and N uptake, particularly from the subsoil, that often resulted in higher grain protein. Canola also appears to have impacts further down the rotation. Field studies indicate that second and third wheat crops in a sequence can yield up to 13% more

3 when the sequence commences with canola rather than wheat. In some cases these residual benefits can be explained by the continuing benefits of lower root disease levels, in others the mechanism is unclear. Despite the generally increased yield of wheat after break crops, wheat is often grown after wheat due either to the lack of profitable break crops (in drier or unsuitable areas) or in response to higher relative prices for wheat. In a three year crop sequence experiment near Junee from the most profitable crop sequence was wheat-wheat-wheat. Low initial disease following a winter-cleaned pasture in 1993, a drought in 1994 and late stubble burns throughout the sequence minimised disease build-up. Wheat was also more profitable (or at least minimised loss!) in the drought. Other management strategies to reduce risk in wheat-wheat sequence include PredictaB soil disease tests prior to sowing, delayed sowing, and delayed or adjusted N topdressing to suit seasonal and/or disease conditions. Evidence of declining canola yields? Canola yields in southern NSW are at best static, at worst declining and most certainly below the average water-limited potential. The evidence for the declining performance of canola comes from several sources including: District average yields show a steady decline in shires in southern NSW since 1995 compared to nearby shires in central NSW Consultants report that the WUE of crops has also declined during that period, even for the leading growers Declining canola yields was consistently identified as the highest priority research area in a 2002 survey of 26 grower groups in the area. The expected performance of canola, around 50% of wheat yield, was no longer achieved and many growers were reducing the area sown. Growers and their consultants in the Harden area took the initiative to investigate the reasons for the poor canola performance by developing the Grain Growers Australia funded Best Bet Canola Management Project in The project involved leading growers, consultants and researchers and was focussed on identifying and overcoming the constraints to canola yield. The approach has been recently expanded into areas further west and south through the FarmLink Canola- Plus project, and in the north by Greenethorpe Grenfell Cropping Group. A GRDC-funded paddock survey across the whole region co-ordinated by FarmLink was also initiated in In this paper we present some of the key findings from the projects to date.

4 Disease - the key problem? The Best Bet Committee identified disease as the key factor likely to be limiting yields in the higher rainfall eastern areas ( mm). The diseases Blackleg and Sclerotinia were of most interest, and the experimental design and treatments reflected the focus on these diseases. Each site had three sowing dates (late April - mid June), two varieties (Blackleg rating 9 and 6.5), six fungicide treatments on seed and/or fertiliser, and foliar fungicide sprays for Sclerotinia. The group has now compiled three seasons of data from The results from the BBC project to date support the initial assertion that disease was a key factor limiting yields in the higher rainfall areas. In treatments and/or seasons in which both diseases were controlled, canola yielded to its water limited potential as estimated using the APSIM Canola simulation model. Key outcomes for Blackleg fungicide research are: (see Table 1) Both Jockey and Impact reduce lesions at cotyledon stage Jockey was ineffective in reducing lesions after the cotyledon stage Jockey and Impact can both reduce lodging and increase yield Impact was generally more effective but has higher cost No extra yield benefit from using both fungicides Maxim XL did not suppress the development of lesions or reduce lodging. Table 1: Effect of fungicide treatment on disease and yield in canola cv. Rainbow (Galong, sown 2003) Treatment % Plants Infected Cot 2-4 leaf 6-8 leaf % Lodging Yield t/ha 1. Untreated 41.3 a 84.7 a 90.7 a 10.3 a 2.17 a 2. Maxim 48.7 a 80.7 a 98.3 a 10.3 a 2.18 a 3. Jockey 9.3 b 85.3 a 83.4 a 7.3 b 2.11 a 4. Impact 7.3 b 18.7 b 46.8 b 1.0 c 2.33 a 5. Jockey + Impact 6. Maxim + Impact 0.7 b 6.7 b 26.4 c 0.7 c 2.32 a 6.0 b 20.7 b 34.5 bc 1.0 c 2.82 b Values followed by the same letter down a column are not significantly different at P <0.05 For updated advice on Blackleg control see "Australian Blackleg Management Guide" Key outcomes for Sclerotinia research are: (see Tables 2a, 2b)

5 Significant yield benefits from controlling Sclerotinia in 2001 but not in 2002/3 Optimum spray timing appears to be at 20-50% flowering and just prior to rain Petal infection levels are not a good predictor of stem infection levels or yield impacts Environmental conditions which result in high Sclerotinia are not fully understood or easily predicted Decision rules for economic spraying are currently not straightforward. Table 2a. Response to Sclerotinia control in 2001 Site % Yield Responses Yield Responses (t/ha) % Stems Infected Wallendbeen Galong Table 2b. Response to Sclerotinia control in 2003 Site Petal Test % % Stem Inf. Yield Response Economic Response Galong No No Grenfell t/ha No Wallendbeen No No Wallendbeen No No Cowra No No Don't forget the basics The Best Bet and FarmLink experiments have all utilised "best bet" approaches to canola production while investigating the impacts of disease. The results have reinforced the importance of early sowing, careful nutrient management and care at harvest to avoid unnecessary losses. Wheat stubble reduces canola growth Canola generally grows poorly when sown into surface retained wheat stubble (5 t/ha wheat stubble reduced yield by around 25%). Recent research has shown that the problem is due to the slower emergence of the canola seedling through the straw layer, the extra investment of dry matter in hypocotyl (stem) needed to emerge, and the colder minimum temperatures experienced by the growing tip above the straw layer. These all slow the growth rate and development of leaf area.

6 There was no evidence that phytotoxins from the straw (allelopathy) was involved. Sowing techniques using wider rows, narrow points and press-wheels that move stubble off the seeding row and into the inter-row alleviated the growth reductions associated with 5t/ha of surface-retained wheat stubble, and resulted in similar yield to burnt treatments. At lower rates of stubble (<2 t/ha) most sowing processes adequately push the straw off the seeding row and reduce impacts on canola. It is possible that allelopathy may be a problem if the wheat straw is pinned into the seeding row at sowing or if large amounts of straw are incorporated immediately (1-2 week) prior to sowing. Under these circumstances, rotting straw in close proximity to germinating seeds may cause phytotoxic effects on the seedlings. Disclaimer Any recommendations, suggestions or opinions contained in this publications do not necessarily represent the policy or views of the Grains Research and Development Corporation. No person should act on the basis of the contents of this publication without first obtaining specific, independent professional advice. The Grains Research and Development Corporation will not be liable for any loss, damage, cost or expense incurred or arising by reason of any person using or relying on the information in this publication.