ABSTRACT

From 1996 to 1998 two experiments were sown each year in Northern and/or Eastern Tasmania. Experiments were designed to determine the seed yield performance of a range of commercially available canola varieties. In 1996 only four varieties were evaluated, while in 1997 the number of varieties was expanded to 12 including four triazine tolerant varieties. Two more varieties were included in 1998. Sowing times ranged from April to October. Yields ranged from under 0.5 t/ha at an October sown site under severe moisture stress in 1996 to over 5t/ha at an Autumn sown non-irrigated site in 1998. The best seed yield from an irrigated site was 5t/ha for an August sowing in 1997. Significant differences between varieties occurred at each site with early maturing varieties generally giving the best seed yields. The triazine tolerant varieties were significantly lower yielding than the conventional varieties. The 1998 experiments illustrated the benefit of autumn sowing which yielded approximately 2t/ha more than the adjacent spring sown site. From this work preliminary variety recommendations can be made to farmers intending to grow canola. However further autumn sown experiments need to be conducted before any conclusive recommendations can be made for early sowings. Raised bed cropping will play an important role in the establishment of an oilseed industry in Tasmania as Autumn sowing will expand in traditional cropping areas allowing winter cropping of normally winter waterlogged soils. It is anticipated that an oilseed processing facility will be developed in Tasmania providing farmers in both traditional cropping and wool production areas with a viable cropping option.

INTRODUCTION

A range of factors are contributing to the interest in establishing an oilseed industry based on canola in Tasmania. Growers from both traditional dryland cropping and wool production areas require an option other than cereals for their cropping systems. It is anticipated that processing facilities will be established to receive crop from the 1999/2000 season. Evaluation of presently available varieties is being undertaken to determine the most suitable for Tasmania’s cool temperate climate.

Traditionally dryland crops have been mostly spring sown, however the introduction of raised bed cropping will change the emphasis to higher yielding autumn sown crops. Raised bed cropping has the potential to prevent crop losses in regions with soils subject to winter waterlogging problems. However it is anticipated that many growers will be inclined to grow spring sown canola. Traditional woolgrowers have increased the area sown to cereals in response to the decline in wool prices in recent years. Many of these growers can sow crops in autumn sow crops and generally consider crops, other than cereals, to be not viable. Canola is considered a viable option in these regions.

Work has been undertaken at various times to develop a canola/rapeseed industry in Tasmania. Garside (1975) conducted experiments in the early 1970’s that showed good yields could be obtained, however up until 1975 the only commercial crops were grown in 1972/73. These crops (150 ha) were spring sown in various regions of Tasmania. Due to the dry spring and summer weather yields were generally poor with a best yield of 2.5t/ha. Russell (1980) reported that in 1978/79 200 hectares were sown in the far North West of Tasmania with yields of 1 to 2.5t/ha. The following season 2000ha were sown across Tasmania with yields ranging from 0.5 to 2t/ha in Northern Tasmania and 3t/ha in the far North West. All the crops were spring sown. Each attempt to establish a sustainable commercial industry was unsuccessful primarily due to the lack of a local market.

Work reported by Mendham et al (1989) reported that high yields of over 5t/ha could be achieved with canola/rapeseed in Tasmania. Three cultivars of differing maturity were evaluated, Wesbell (late), Marnoo (mid season) and RU1 (early) in time of sowing experiments over six sowing times at a higher rainfall site in Northern Tasmania and a lower rainfall site in Southern Tasmania. Sowing dates ranged from May to October. Yields at the higher rainfall site ranged from 3 to 4t/ha from the May to early September sowings after which they declined with later sowings. Varietal yields were similar for each sowing with the exception of the May sowing where Marnoo yielded approximately 1t/ha greater than Wesbell and RU1. RU1 and Wesbell yielded similarly from the May sowing after which RU1 yielded far less than the other varieties until an early September sowing, after which yields became similar for each variety. At the low rainfall site RU1 yielded slightly less from the earlier sowings than the other varieties. From the late August sowing RU1 yielded slightly more than Marnoo and increasingly more than Wesbell for each later sowing. It was concluded that varietal earliness was only a slight advantage for late sowings, but the benefits were greater where moisture stress limited potential yield.

The objective of the present work is to identify the highest yielding commercially available varieties for Tasmania’s cool temperate climate. Two experiments conducted each year from 1996 to 1998.

METHODOLOGY

All experiments used a randomised complete block design with four replications. Plots were sown with a cone seeder into a prepared seedbed to which trifluralin had been applied and incorporated. The sowing rate for each variety was determined by target seedling densities of 80-120 plants/m². All plots were direct harvested after desiccation. Samples were weighed off header and sub-samples collected for laboratory analysis to determine oil percentages. Data was analysed by analysis of variance using the Rothamsted Genstat software package. Yield data was not adjusted for edge effect. Insects were controlled as necessary.

1996 Sites

Two sites were spring sown, one at the Cressy Research Station (CRS96) in the Northern Midlands of Tasmania and one at Cranbrook (C96) on the East Coast of Tasmania. CRS 96 was sown on the 29/10/96 and harvested on the 28/2/97. C96 was sown on the 16/10/96 and harvested on the 27/2/97. Plots were pre-drilled with pre-drilled with an NPK mix of 4-6-7 plus molybdenum and boron trace elements at 300kg/ha. Plots at both sites were 20m x 3m. Monthly rainfall is shown in Table 1.

Table 1. Rainfall (mm), plus irrigation (*), at Cressy and Cranbrook 1996/97

1997 Sites

One site at Cranbrook (C97) site was sown on the 27/8/97 and harvested on the 16/1/98. Another site at Formosa (F97), a property adjacent to Cressy Research Station, was sown on the 30/9/97 and harvested on the 11/2/98. C97 was pre-drilled with an NPK mix of 4-6-7 plus molybdenum and boron trace elements at 300kg/ha, while F97 was pre-drilled with 200kg/ha of the same fertiliser. C97 was top dressed with 240kg/ha of DAP prior to budding while F97 was top dressed with 90kg/ha of Nitram. The plot size for C97 was 20m x 3m and for F97 plots were 20m x 1.5m. Rainfall for both sites is shown in Table 2.

Table 2. Rainfall (mm), plus irrigation (*), at Cressy and Cranbrook 1997/98.

1998 Sites

An autumn sown site (CRS98AU) and a spring sown site (CRS98SP) were sown at the Cressy Research Station on the 28/4/98 and 25/8/98 respectively. CRS98AU was pre-drilled with an NPK mix of 4-6-7 plus molybdenum and boron trace elements at 600kg/ha while CRS98SP was pre-drilled with 300kg/ha of the same fertiliser. Plot sizes were 18m x 1.5m. CRS98AU was harvested on the 30/12/98 and CRS98SP was harvested on the 13/1/99. CRS98AU was topdressed with 60 kg/ha of nitrogen while CRS98SP received 70kg/ha of nitrogen. Rainfall for both sites is shown in Table 3.

Table 2. Rainfall (mm) at Cressy 1998/99.

RESULTS

The results (Tables 4 to 6) show significant differences between varieties at each site, with the exception of the C96 experiment. At all sites the best yields were from the earlier maturing varieties while the triazine tolerant varieties were lower yielding. The highest yielding experiment, CRS98AU, had the longest growing season (see Table 7) of 247 days, with the next longest growing season for the irrigated C97 experiment which was 174 days.

Table 4. Yield and oil results for 1996 experiments at Cressy and Cranbrook.

Table 5. Yield and oil results for 1997 experiments at Formosa and Cranbrook.

Table 6. Yield and oil results for 1998 experiments at Cressy.

* Oil % not available.

Table 7. Days to harvest from sowing for all experiments.

DISCUSSION

The objective of the experiments to determine the varieties most suitable for Tasmania has not been conclusive to date. It was expected that early maturing types varieties be more suitable for spring sowing when earliness should be an advantage. Variety yields from the autumn sown trial CRS98AU also showed that early maturing varieties are generally higher yielding than the mid and late maturing types. Autumn sowing was not expected to indicate that early maturity would be an advantage for higher yields.

The spring sown C96 experiment was not irrigated and suffered moisture and heat stress, as reflected in the yields. Dunkeld (mid to late maturing) yielded approximately half of Hyola 42 (early maturing), the highest yielding cultivar at this site. This suggested that late maturing varieties are at a disadvantage from late dryland sowings. This trend was repeated in the spring sown CRS96 experiment, although the yield differences were not as large and were not statistically significant. The penalty for late maturity appears in part to be reduced by irrigation reducing moisture stress. The consistent yields of Oscar, having the second highest yield at each site does not suggest mid season maturing varieties are penalised by late sowing. Ranking of yield performance of the varieties in both the 1996 experiments was the same.

The 1997 experiments were both irrigated, with the August sown C97 experiment having higher yields than the late September sown F97 experiment and having a 39 day longer growing season. The results from C97 were confounded by both Dunkeld and Range having reduced yield due to harvest losses of up to 20%. An addition of 20% yield for each of these varieties would increase their yields to be comparable with the highest yielding varieties, Monty, Oscar and Hyola 42. The yield differences between the trials where the earlier sown C97 experiment yielded approximately 2t/ha more than the later sown trial indicates time of sowing influences yield more than varietal maturity type.

The 1998 experiments were conducted on adjacent sites at Cressy Research Station to not only assess varietal performance but also provide a reasonable comparison between early and late sowing. The highest yielding varieties in both experiments were dominated by early maturing types. Scoop yielded much better than in the 1997 trials. Monty and Hyola 42 were again the most consistent varieties across both experiments. The time of sowing appeared to have a greater influence on yield than varietal differences.

The experiments clearly show the advantages from earlier sowing. With the exception of the results from 1996, the experiment with the longest growing season resulted in the highest yield. The experiments in which the highest yields were recorded in 1997 and 1998 had a longer growing period of 39 and 105 days respectively compared to the other experiments in each of those years.

CONCLUSION

Preliminary varietal recommendations can only be made for spring sowing. Early maturing varieties showed the most consistent yield performance, while the yields of the mid to late maturing types were generally lower. Further autumn sowing evaluations are required before conclusive variety recommendations can be made to growers. Other factors must also be considered such as blackleg tolerance, early vigour and oil percentages. Based on the results from these experiments and agronomic data from mainland Australia, Monty is presently considered the most reliable variety under Tasmanian growing conditions for all sowing times.

The experiments do show the advantages of early sowing as yield declined with later sowings. Raised bed cropping in Tasmania will shift the emphasis to autumn sowing in areas of traditional winter waterlogging soils with expected higher yields from early sowing. Future work will focus on autumn sown trials, with some on raised beds, to determine varietal performance under conditions conducive to high yields.

ACKNOWLEDGMENTS

Thanks must be expressed to Nick Waschman, Rob Decesare, and Gary Martin for their technical support, Stuart Smith for scientific support and guidance in this project, and Wayne Burton and Dave Robson for seed and general advice.

REFERENCES

1. Garside, A., (1975), Rapeseed, varieties, times of sowing and cultural recommendations, Tasmanian Journal of Agriculture, August 1975 121-126.

2. Mendham, N.J., Russell, J., & Jarosz, N.K., (1990), Response to sowing time of three contrasting Australian cultivars of oilseed rape (Brassica napus), Journal of Agricultural Science, Cambridge 114 275-283

3. Russell, J., (1980), Rapeseed in Tasmania, Tasmanian Journal of Agriculture, August 1980 57-61.