Improving canola profit in central NSW: effect of time of sowing and variety choice

Leigh Jenkins¹ and Rohan Brill²

¹NSW DPI Warren, ²NSW DPI Coonamble

Key words

Canola, establishment, time of sowing, variety, flowering

GRDC code

DAN00129 – Variety Specific Agronomy Packages for Northern NSW

Introduction

Canola is an important winter crop rotation option in western NSW. The advent of new varieties in all four herbicide groups has enabled widespread adoption over recent years. As for all areas where canola is produced, timely and uniform establishment remains a critical factor in the success of the crop. Sowing date is known to be an important management strategy to optimise yield of canola in all canola regions.

Time of sowing is a compromise between ideal sowing conditions and the appropriate maturity cultivar to suit. Early sowing maximises vegetative growth (biomass) and the length of flowering period, but can predispose the crop to yield-damaging frosts at flowering and early grain fill. Later sowing may reduce frost risk but can result in poor vigour due to cold and/or wet soils at planting time, and an inability to complete seed maturity before the onset of high temperatures and moisture stress, reducing both yield and oil content.

NSW DPI recommends sowing canola from early-mid April to early May in the central-west zone (Condobolin-Nyngan), regardless of soil type. For western NSW regions, warm soil conditions in April which can enable more vigorous establishment of current varieties, are often offset by lack of soil moisture in the seedbed at planting time. This paper reports on the results of a trial conducted in 2012 to investigate the effect of three times of sowing on yield and oil content of seven canola varieties (hybrid and open pollinated), and evaluates the impact on length of flowering. A seeding rate component was also included in the trial (two varieties only) to compare the interactions between sowing time and plant population, especially to investigate if early sown low density crops (less than 15 plants/m²) yield comparably with early sown higher density crops (more than 20 plants/m²). 

2012 trial details

The 2012 canola time of sowing trial was conducted at Trangie Agricultural Research Centre on a grey vertosol (cracking clay) soil (Colwell 22 ppm, 0-10 cm). The trial was sown with 80 kg/ha Granulock SupremeZ (11 % N, 22 % P, 4 % S and 1 % Zn), using a Morris Contour Drill planter with the fertiliser placed directly with the seed. The trial was topdressed with 100 kg/ha GranAm (21 % N, 24 % S) on 1 June, ahead of 9 mm rain on 2 June.

Table 1 indicates the dates and respective conditions at each time of sowing. Dates and conditions were chosen to reflect typical risk scenarios experienced by growers across the region. Table 2 shows the variety treatments. There were seven varieties planted to compare a range of canola types, including early vs. mid season maturity, hybrid vs. open-pollinated, and herbicide tolerance: conventional, triazine tolerant (TT) and imidazolinone tolerant (CLF). All seed was sourced “as new” for this trial.

Table 1: Sowing dates, sowing depth and conditions for canola time of sowing trial, Trangie ARC 2012

Table 2: Variety characteristics, target plant population, number of seeds planted, seed size and actual sowing rate for canola time of sowing trial, Trangie ARC 2012

Note that total establishment was assumed to be 48% (rounded up to 50%) based on germination of 80% and field establishment of 60% (industry standard figures). Hence where 40 plants/m² was the target density, 80 seeds/m² were actually sown; and where 15 plants/m² was the target density, 30 seeds/m² were actually sown.

Note also that the canola varieties used in this trial were chosen to be representative of particular herbicide, plant type and maturity groups, therefore seed companies may market other varieties with similar or better potential to the varieties used in this trial.

Results

Effect of time of sowing on establishment

Date and days to emergence (as an average for all varieties) were recorded for the three times of sowing as TOS 1, 24 April (11 days); TOS 2, 4 May (8 days) and TOS 3, 28 May (14 days). Plant counts (Figure 1) were conducted progressively for each time of sowing once there was no recorded change in emergence scores (conducted three times per week).

Figure 1: Establishment of seven canola varieties with two target plant populations at three sowing times, Trangie ARC 2012

All varieties had reduced establishment from TOS 1, regardless of type (open pollinated or hybrid) or seed size. TOS 1 was moisture-seeked 5 cm deep into marginal moisture because there was no actual rainfall event in early April to plant on. It is possible that depth of sowing at TOS 1 may have had a greater effect on establishment than lack of moisture at sowing. For the standard target plant population (40 plants/m²), the average of all varieties was 16 plants/m², with only two hybrids (Hyola 555TT and 43Y85 CL) achieving greater than 25% establishment (i.e. plant count greater than 20 plants/m², from 80 seeds/m² planted). For the low seeding rate (target 15 plants/m²) the average was less than 7 plants/m² (i.e. less than 25% target establishment from 30 seeds/m² planted). The variety AV-Garnet had the lowest plant count at both seeding rates.

Establishment for all varieties at TOS2 and TOS 3 achieved greater than the target plant population, because plant establishment was greater than the assumed 50% on which seed rates were calculated. This could be due to either the shallower sowing depth and/or follow-up rainfall received post-sowing. TOS 2 dry-sown at 2 cm depth emerged quicker than either TOS 1 or TOS 3, once follow-up rain was received. The average plant counts for the standard sowing rate (target 40 plants/m²) was 48 plants/m² (60%) for both TOS 2 and TOS 3, whereas for the low sowing rate (target 15 plants/m²) TOS 2 achieved 18 plants/m² (60%) and TOS 3 achieved 20 plants/m² (67%).

In terms of variety effect, the three hybrids with seed size greater than 4 g/1000 seed weight (Hyola 555TT, 43Y85 CL and 44Y84 CL) averaged 74% establishment of seeds planted/m², compared to the four open-pollinated varieties with seed size of less than 4 g/1000 seed weight, which averaged 61% establishment of seeds planted/m².

Effect of time of sowing on length of flowering

Previous canola time of sowing trials have suggested that late sowing shortens both the vegetative and reproductive phases of canola through temperature and photoperiodic effects, as well as increased water stress during the grain fill period. Flowering observations conducted at weekly intervals to assess the impact of time of sowing on length of flowering are summarised in Figure 2 below to highlight 10% start flower, 100% full flower and 10% end flower.

Flowering descriptions are defined as follows:

• 10% start flower: the date when 10% of plants in the crop (plot) have commenced flowering
• 100% full flower: the date when 100% of plants in the crop (plot) are in full (maximum) flower, i.e. the crop is bright yellow with all branches flowering. Some early pods may be visible in the lower section of branches.
• 10% end flower: the date when 10% of plants in the crop (plot) have flowers remaining at the top of the branch. The lower 90% of the branch will have pods formed or forming.

Figure 2: Length of flowering of seven canola varieties with two target plant populations at three sowing times, Trangie ARC 2012

Note that the following observations are based on calendar days which do not take into account the difference in thermal time (accumulated day degrees) between each TOS treatment. Temperature effects are a major driver of plant growth and development in canola. As an example, TOS 1 would have accumulated more day degrees in the month of May than TOS 3. Note also that these comments are based on observational data which has not been statistically analysed.

For each canola variety, the length (calendar days) of the vegetative period was reasonably consistent regardless of time of sowing, within a range of approximately 10 days variation between TOS treatments. There were differences between varieties in average length of vegetative period. The longer season varieties Jackpot TT and AV-Garnet averaged over 100 days. The short season varieties 43Y85 CL and ATR-Stingray averaged 90 and 92 days respectively. The lower seeding rate lengthened the vegetative period for 44Y84 CL in TOS 1 only (by 4 days); but shortened the vegetative period for AV-Garnet by 4 days at TOS 1 and lengthened it by 5 days at TOS 2.

There were differences in the total length (calendar days) of flowering period as a time of sowing effect. For each canola variety in this trial (including those planted at lower seeding rates), total length of flowering period was shortened as sowing was delayed. Length of flowering periods averaged for all varieties were 62 days (TOS 1), 55 days (TOS 2) and 47 days (TOS 3). Some varieties showed a greater difference between TOS 1 and TOS 2 (e.g. 43Y85 CL, 13 days, and 44Y84 CL, 11 days), whereas other varieties were more impacted by the delay from TOS 2 to TOS 3 (e.g. AV-Garnet, 12 days and Jackpot TT, 10 days). The Pioneer Clearfield® varieties appeared to be more affected (up to 20 days shorter flowering period) than the triazine tolerant varieties. The lower seeding rate treatments had opposite effects on the two varieties. For 44Y84 CL_Low, flowering period was 1.5 days shorter at TOS 1 but 2-3 days longer at TOS 2 and TOS 3 than 44Y84 CL. For AV-Garnet_Low, flowering period was 4 days longer at TOS 1 but up to 5 days shorter at TOS 2 and TOS 3 than AV-Garnet.

Effect of time of sowing on yield

There were significant differences in yield (Figure 3) between variety and time of sowing. However there was no significant interaction between variety and sowing time, meaning that varieties performed relatively consistently regardless of when they were planted.

Figure 3: Grain yield (t/ha) of seven canola varieties sown at three sowing times, Trangie ARC 2012

l.s.d. (p = 0.05) Variety = 0.16 t/ha, Sowing time = 0.1 t/ha

The effect of time of sowing, averaged for all varieties, showed that TOS 3 was significantly higher yielding than TOS 1 (0.54 t/ha) and TOS 2 (0.11 t/ha). TOS 2 was significantly higher yielding than TOS 1 (0.43 t/ha). The lower yield of TOS 1 was likely due to a combination of factors including reduced plant establishment, frost damage as a result of early flowering and potentially higher rates of vegetative water use.

The hybrids 44Y84 CL and 43Y85 CL were the highest yielding varieties in this trial, with an average yield (across all sowing times) of 1.72 t/ha and 1.62 t/ha respectively. Jackpot TT and ATR Stingray were the lowest yielding varieties, with an average yield (across all sowing times) of 1.15 t/ha and 1.07 t/ha respectively.

The seeding rate treatment had a significant effect on yield (p = 0.002) in this trial. Averaged for the two varieties 44Y84 CL and AV-Garnet, the high seeding rate targeting 40 plants/m2 yielded 0.24 t/ha more than the low seeding rate targeting 15 plants/m2 (l.s.d. seed rate 0.14 t/ha, p = 0.05). There was no interaction between seeding rate and sowing time, meaning that the advantage of the higher seeding rate was observed for all sowing times.

Effect of time of sowing on oil content

There were significant differences in oil content between varieties (Figure 4), but no significant difference as a result of time of sowing. Jackpot TT had the highest average oil content (43.2%) of all varieties, with 44Y84 CL also higher than the other five varieties (42.1%). All other varieties averaged less than the minimum base oil content of 42%, meaning discounts would apply at delivery. The lowest of these were 43Y85 CL at 40.8% and Hyola 555TT at 40.6%

There was no significant effect of seeding rate treatments on oil content in this trial.

Figure 4: Oil (%) at 6% moisture of seven canola varieties averaged across three sowing times, Trangie ARC 2012

l.s.d. (p = 0.05) Variety = 0.6 %

Discussion

Previously published time of sowing trial data suggests that as a general rule, early sowing (early-mid April) predisposes the crop to greater frost risk during flowering. Delayed sowing (late May – late June in southern grain zones) can result in reduced yield potential due to a combination of factors including a shortened vegetative period (reduced crop biomass), reduced length of flowering period, and moisture and high temperature stress at grain fill.

This trial focussed on the early sowing period for western NSW, from mid-April to early May. TOS 1 (13 April) was moisture-seeked into marginal moisture at 5 cm depth, resulting in an average of less than 25% establishment of target plant densities. TOS 2 (26 April) showed that dry sowing can be a viable option for canola provided there is a reliable forecast of follow-up rain (15 – 20 mm). TOS 2 received 14 mm rain on 2 May and had begun emerging by 4 May. TOS 3 (14 May) was sown into good moisture and received 21 mm follow-up rainfall. Both TOS 2 and TOS 3 achieved greater than the targeted plant densities because the field establishment % was greater than the assumed 50 %.

The 2012 Trangie trial confirmed previous studies that length of flowering period is reduced as time of sowing is delayed, regardless of variety maturity. However the shortened flowering period of TOS 2 and TOS 3 compared to TOS 1 did not translate into reduced yield or oil content, with both TOS 2 and TOS 3 having significantly higher yields (as an average for all varieties) than TOS 1, and no significant difference in oil content.

The most likely contributing factor for the reduced yields of TOS 1 was greater frost damage. Frost impact data (number of aborted pods) was collected at the end of flowering but this data had not been analysed at the time of submitting this paper. Meteorological data from Trangie ARC weather station supports grower observations that 2012 had an unusually high number of frosts during the late winter – early spring period. There were 59 frosts (defined as less than 2°C recorded in Stevenson screen) from 1 May to 30 September in 2012. There were several periods of consecutive frosts from late July to early September. Some of these frost events were severe, for example three days of less than -3.0°C recorded 31 July – 2 August. Since TOS 1 commenced flowering earlier (average for all varieties 17 July) and flowered for a longer period than TOS 2 or TOS 3 (commenced on average 2 August and 16 August respectively) it is assumed that TOS 1 was more affected by frosts during flowering.

More research is required to investigate the effect of early sowing on vegetative water use. Since the early sowing date resulted in plants growing in May in relatively warm temperatures, water use may also have been higher, leaving less water available for grain fill.

Conclusion

Conditions at sowing can impact on crop establishment rates. Moisture seeking early (mid-April) into marginal moisture conditions may reduce establishment. Delaying sowing until there are better moisture conditions after an autumn break (early May), and even dry sowing (at a shallow depth) prior to the autumn break can be acceptable for canola provided adequate rainfall (15 – 20 mm) is received soon after sowing. In the 2012 trial if May had remained dry, the early deep sown treatment may still have resulted in a better outcome than not planting canola at all.  Seeding rates that target a lower plant population may reduce yield potential. However the greatest risk associated with early sowing is the impact of frost which may significantly reduce the yield potential of early planted (mid-April) canola in western NSW.

Acknowledgements

Canola seed was sourced as new for all 2012 VSAP trials, and the generous donations of the following are gratefully acknowledged: John de Lyall, Pioneer; Chris Fletcher, Pacific Seeds; Chris Roberts, Nuseed; and Ed Nixon, AgNVet Warren.

The assistance of Tim McNee (District Agronomist Nyngan), Jayne Jenkins and Robert Pither (technical assistance) in the conduct of these trials is gratefully appreciated.

Meteorological data for Trangie ARC weather station accessed by Kevin Moore.

GRDC project funding: Variety Specific Agronomy Packages for Northern NSW.

Contact details

Leigh Jenkins
NSW Department of Primary Industries
0419 277 480
leigh.jenkins@dpi.nsw.gov.au

Reviewed by

Don McCaffery – Technical Specialist (Pulses and Oilseeds) NSW DPI, Orange.