ABSTRACT

Canola cultivars were compared at a low rainfall and a medium rainfall site in South Australia in 1998 with two row spacings and a range of sowing rates. Cultivars that varied considerably for early plant vigour responded similarly to varying sowing rate, indicating that the same sowing rates could be used for hybrid, conventional and triazine tolerant cultivars of canola. Grain yield increased up to plant densities of about 50 plants/m² and was unaffected between 50 and 130 plants/m². Even at densities as low as 20 plants/m², maximum yield was only reduced by 12-16%. Row spacing had little effect except at the low rainfall site where 30cm rows produced 9% less yield than 15cm rows. This may be due to the reduced time from sowing to flowering for early maturing cultivars of canola, which reduces plant compensation in wider row spacings in low rainfall environments. Oil content was unaffected by row spacing or plant density. Therefore in stubble retention systems, growers can increase row spacing to allow stubble flow, with little or no effect on yield or quality, especially in medium to high rainfall environments.

INTRODUCTION

Sowing rates for canola in Australia have traditionally been about 5 kg/ha with the aim of establishing between 50 and 80 plants/m². In general, this has resulted in adequate plant stands except where pests such as insects, birds or mice have reduced plant numbers at or soon after plant emergence. Traditional row spacings have been between 15 and 18 centimetres; however, the increased interest in retention of stubble has seen many farmers increase row spacing to as much as 36 centimetres to allow for the flow of heavy stubbles through the seeding equipment. Breeding programs have now developed a range of canola cultivars which vary in early plant vigour. These cultivars vary from some hybrids and conventional cultivars which exhibit a high degree of early vigour to the triazine tolerant cultivars which produce very slow growth during winter.

The aim of this study was to determine the effect of row spacing and plant density on yield and oil content of canola cultivars which varied in early plant vigour at low and medium rainfall sites in South Australia.

MATERIALS AND METHODS

Split-plot trials were sown at Lameroo (low rainfall) and Bordertown (medium rainfall) in South Australia in 1998, with cultivars as main plots, row spacings (15 and 30 cm) as split plots and sowing rates (25, 50, 75, 100, 150, 200 seeds/m² ) as split-split plots. Cultivars used were Hyola 42 (hybrid) and Monty at Lameroo and Dunkeld and Pinnacle(triazine tolerant) at Bordertown. Cultivars at each site had similar maturity but differed in early plant vigour. Plots were 10 m long by 8 rows (15cm row spacing treatment) or 4 rows (30 cm row spacing treatment) and 4 replicates were used. All plots were weed free and received adequate fertiliser. Plant densities were counted on two quadrats per plot when the plants were at the two leaf stage.

Plots were harvested by machine to determine grain yield, while oil content was analysed using an NIRSystems 4500 scanning NIR spectrophotometer.

RESULTS AND DISCUSSION

Trials were sown on 6 May and 26 May at Lameroo and Bordertown respectively, within the normal range of sowing dates. Growing season rainfall (April to October) at Lameroo (267 mm) and Bordertown (358 mm) was similar to the long term average but was characterised by an early start and a dry finish, particularly at Bordertown.

Grain yield

While no difference in grain yield occurred between cultivars at Lameroo; at Bordertown the conventional cultivar Dunkeld yielded 28% greater than the TT cultivar Pinnacle. This yield penalty of TT canola in Australia has been reported elsewhere (Potter and Salisbury 1993). Row spacing had no effect on grain yield at Bordertown, but at Lameroo the 15cm row spacing produced significantly greater yield than the 30cm spacing (1450 and 1327 kg/ha respectively). Narrow rows have also been reported to give higher grain yields than wide rows in Brassica napus (Morrison et al. 1990).

Table 1. Effect of plant density on grain yield of canola cultivars at Lameroo and Bordertown in 1998

a,b Means followed by the same letter are not significantly different at P=0.05

Plant densities established at all sowing rates were slightly higher at Lameroo than at Bordertown

( Table 1.). This may be due to the drier conditions at sowing at Bordertown with a lack of rain through mid and late May. At both sites, grain yield increased up to plant densities of about 50 plants/m² and was unaffected between 50 and 130 plants/m². However, even at densities as low as 20 plants/m² maximum yield was only reduced by 12-16%. Similar results have been reported by McGregor (1987), Van Deynze et al. (1992) and Leach et al. (1999). No interaction occurred between cultivar and sowing rate, indicating that cultivars with considerable differences in early vigour responded similarly to varying sowing rate. Van Deynze et al. (1992) in Manitoba also reported a lack of cultivar by sowing rate interaction between conventional and hybrid cultivars, even where hybrids produced 24% higher yields and 50% higher total dry matter than conventional cultivars.

Grain weight

Grain weight was greater at Lameroo than at the higher rainfall site at Bordertown (Table 2). This was due to lower yields at Lameroo and more rainfall during grain fill than at Bordertown. At both sites there was a significant cultivar by sowing rate interaction for grain weight but no effect of row spacing. Grain weight increased as sowing rate increased. Increases in grain weight with sowing rate were also reported by McGregor (1987) and Leach et al. (1999). However; in this study, the cultivar that was most affected by sowing rate varied from the less vigorous Monty at Lameroo to the more vigorous cultivar Dunkeld at Bordertown.

Table 2. Effect of sowing rate and cultivar on grain weight (g/1000 grains) at Lameroo and Bordertown in 1998

Oil content

Oil content was not affected by cultivar, row spacing or sowing rate at Lameroo, and was only affected by cultivar at Bordertown where Dunkeld (40.3%) produced more oil than Pinnacle (37.0%). A lack of any effect of sowing rate on oil content has also been reported by Morrison et al. (1990) and Leach et al. (1999) while Van Deynze et al. (1992) showed a small decrease in oil content as sowing rate increased to 9 kg/ha. Similarly, Morrison et al. (1990) found few consistent effects of row spacing on oil content. In practical terms it seems that row spacing and sowing rate can be varied with little effect on oil content; this is of particular relevance in Australia where farmers are paid a premium for oil content over 40% and penalised for less than 40%.

CONCLUSIONS

Cultivars that varied considerably for early vigour responded similarly to varying sowing rate. Therefore growers can use the same sowing rates for hybrid, conventional or triazine tolerant canola cultivars. Grain yield increased up to plant densities of about 50 plants/m² and was unaffected between 50 and 130 plants /m² . Row spacing had little effect except at Lameroo where 30cm rows produced 9% less yield than 15cm rows. This may be due to the reduced time from sowing to flowering of early maturing cultivars of canola, which reduces plant compensation in wider row spacings in low rainfall environments. Therefore in stubble retention systems, growers can increase row spacing to allow stubble flow, with little or no effect on yield or quality, especially in medium to high rainfall environments.

ACKNOWLEDGEMENTS

Financial support was provided in part by the Grains Research and Development Corporation of Australia. We thank Peter and Fred Maynard, Lameroo and Kraig Johnson, Bordertown for making land available for trials.

REFERENCES

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2. McGregor, D.I. (1987) Effect of plant density on development and yield of rapeseed and its significance to recovery from hail damage. Canadian Journal of Plant Science 67,43-51

3. Morrison, M.J., McVetty, P.B.E. and Scarth, R. (1990) Effect of row spacing and seeding rates on summer rape in southern Manitoba. Canadian Journal of Plant Science 70,127-137

4. Potter, T.D. and Salisbury, P.A. (1993) The role of triazine resistant canola in Australia. 9^th Australian Research Assembly on Brassicas, Wagga Wagga, October 1993, pp. 87-91.

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