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D. Grey

Agriculture Victoria, Rutherglen


Canola was grown at 18 sites across northern Victoria in the years 1993-1995. The optimum water-use efficiency calculated for canola was 18 kg/mm/ha, which is greater than values used in the industry and reported in the published literature. The evaporative loss of rain was 112 mm, which is similiar to reported values for wheat.

Key Words: Canola, water-use efficiency, nitrogen

Canola has become an important part of cropping rotations in Victoria. It appeals to farmers because it provides good gross margins and increased herbicide and crop rotation options. Canola is an effective break crop, as following cereal crops yield well, suggesting a biofumigative effect. A factorial experiment was set up to test canola's responses to nitrogen and sulphur across northern Victoria. Water-use efficiency (WUE) was calculated to compare the relative responses of canola to nitrogen.

Materials and methods

Eighteen sites across the Wimmera, North Central and North East regions of Victoria were sown to canola in 1993, 1994 and 1995. At sites with a pHCaCl < 4.8, fine ground limestone (2.5 t/ha) was incorporated to 10 cm depth to raise the pH to 5.5. Factorial combinations of sulphur (0, 5, 10, 20, 40 kg S /ha applied as fine ground gypsum, 16% S) and nitrogen (0, 50, 100, 200 kg N/ha applied as urea, 34% N) were laid out in a randomised complete block design with three replicates. Plots were 20 m long (15 m at two sites) and 1.42 m wide. Nitrogen was pre-drilled at 10 cm depth immediately prior to seeding. Canola (Brassica napus cv. Oscar) was sown at 7 kg/ha, with 100 kg/ha triple superphosphate (20%P, 1%S), using a cone seeder. Gypsum was applied by hand after sowing. Crops were windrowed at the 40% brown seed stage and yields obtained using plot harvesters. Rainfall data were obtained from farmer records and from meteorological stations at Rutherglen and Dooen.


Growing season (April-October) rainfall (GSR) varied from 263-367 mm in 1993, 120-184 mm in 1994 and 358-490 mm in 1995. Fig. 1 shows the effects of GSR and nitrogen fertiliser on canola yields. GSR was used, since no measurements of subsoil moisture were made. Following the procedure of French and Schultz (1), a potential yield line was drawn to provide an upper boundary to the data points. This line intersects the x-axis at 112 mm of rainfall, and has a slope of 18 kg/mm/ha. The scatter of points also shows good responses to nitrogen fertiliser at many of the sites. Since there were few responses to sulphur in these experiments (2), only the yield data for the 0 kg S/ha treatment are presented.


The ideal growing season of 1993 (no waterlogging) and the dry season of 1994 provided a good spread of growing season rainfall data and give confidence to the positioning of the potential yield line. The two clusters of points to the left of the line represent sites that were thought to have good stored soil moisture reserves at sowing. The 1995 season was characterised by periods of waterlogging at most sites. The data suggest that growing season rainfall in excess of 375 mm causes yield depressions due to waterlogging.

Figure 1: The effect of growing season rainfall and fertiliser nitrogen on the grain yield of canola grown across northern Victoria in 1993, 1994 and 1995.

There have been few published studies on the WUE of canola. WUE values of 10-12 kg/mm/ha are widely used in the canola industry, based on the field experience that the actual WUE is approximately 60% of that for wheat (H. van Rees, pers. comm.). For rainfed canola at Tatura (Victoria), the WUE calculated from the data of Taylor et al. ranged from 7 to 14 kg/mm/ha (3). Even though these crops were sown in mid-late June, the values are consistent with those above. The increased WUE of plot-grown canola can be attributed to edge effects. If the whole crop WUE of canola is close to 12 kg/mm/ha then the plot edge effects have increased yields by about 50%. From figure 1 the loss of rainfall by direct evaporation was estimated to be 112 mm, which is very close to the 110 mm reported for wheat in South Australia (1). Thus, the value reported in this paper supports the 110 mm figure used by the industry for calculating canola WUE.


The WUE of plot-grown canola in Victoria was estimated to be 18 kg/mm/ha and the evaporation figure was 112 mm. In seasons when growing season rainfall exceeds 375 mm, canola WUE is likely to decrease due to waterlogging.


The original project work by B. Walker, E. Buckley and J. Jones, and financial support of the Grains Research and Development Corporation, is gratefully acknowledged.


1. French, R.J. and Schultz, J.E. 1984. Aust. J. Agric. Res. 35, 743-764.

2. Grey, D.L and Jones, J. 1995. Proc. 1st Vict. Cropping Zone Tech. Update Conf. Longerenong, pp. 59-60.

3. Taylor, A.J., Smith, C.J. and Wilson, I.B. 1991. Fert. Res. 29, 249-260.

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