In 2012, averaged across all trials and varieties, establishment (as a percentage of seeds sown) at the 2.5 cm target depth was approximately 66%, with no difference between varieties. All varieties had reduced establishment at the 5 cm sowing depth compared to the 2.5 cm sowing depth with the exception of Pioneer 44Y84 (CL) that had the largest seed (Fig. 1). At the 7.5 cm sowing depth the difference between varieties and seed size became more marked as the largest seeded variety achieved 50% establishment compared to 20% establishment for the smallest seeded variety.

The effect of sowing depth on grain yield in 2012 was less marked than the effect on establishment. At Nyngan and Coonamble, the 7.5 cm target depth yielded approximately 250 kg/ha less grain than the 2.5 cm and 5 cm target depth. At Nyngan, Pioneer 44Y84 (CL) had no grain yield reduction at the 7.5 cm target sowing depth compared with the shallower sowing depths, however there was a significant grain yield reduction for all other varieties as a result of deep sowing. There was no effect of sowing depth on grain yield at Trangie.

In 2013 the overall establishment achieved was less than 2012. At the 2.5 cm sowing depth establishment was approximately 50% with no significant difference between varieties (Figure 2). All varieties had reduced establishment at the 5 cm sowing depth compared with the 2.5 cm sowing depth; however the reduction was less severe for the hybrids than for the open-pollinated (OP) varieties. Establishment was further reduced at the 7.5 cm sowing depth, with a similar hybrid advantage as occurred at the 5 cm sowing depth.

The effect of sowing depth on grain yield was greater in 2013 than 2012 but was still of a lesser magnitude than the effect of sowing depth on establishment. At Nyngan, the grain yield of Pioneer 44Y84 (CL), AV-Garnet^A and Hyola 555TT were all similar for the 2.5 cm sowing depth; however AV-Garnet^A and Hyola 555TT both had a significant grain yield reduction at the 5 cm and 7.5 cm sowing depths, while Pioneer 44Y84 (CL) did not suffer a yield penalty from deeper sowing. At Trangie, all varieties suffered a grain yield penalty as sowing depth was increased but this reduction in grain yield was less severe for the larger seeded varieties.

Is seed size or plant type the key?

To determine if improved establishment is related to hybrid breeding or simply seed size the seed of each variety was graded into two size categories; large (2 - 2.4 mm diameter) and small (1 – 1.4 mm diameter). Twenty seeds of each variety and seed size category were sown at depths of 2.5, 5 and 7.5 cm in pots and placed in a glasshouse.

Similar to the field trial results the 2.5 cm planting depth had the highest establishment percentage and increasing planting depth to 5 and 7.5 cm significantly reduced establishment by 32 and 51% respectively, averaged across all varieties.

The small seeded OP varieties had the poorest establishment for each planting depth (Table 2). The large seeded hybrid and OP varieties had significantly better establishment compared to their respective small seeded varieties at both the 5 cm and 7.5 cm planting depths. Small seeded hybrids had significantly better establishment than the small seeded OP varieties (Table 2). This establishment data suggests that large seed as well as the heterosis advantage of hybrids contributes to improved establishment.

Dry matter of 100 plants was measured 15 days after emergence to give an indication of early plant vigour. The large seeded hybrids had the greatest dry matter accumulation at all sowing depths. Compared with the large seeded treatments, the small seeded treatments (hybrid and OP) accumulated less dry matter and had a greater reduction in establishment where planting depth was increased. The early vigour advantage hybrids displayed over OP varieties that was observed for the large seeded treatments was not observed for the small seeded treatments, with hybrid and OP varieties accumulating similar dry matter per plant.

These glasshouse findings indicate that the establishment and early vigour advantage of hybrids is mostly due to their larger seed size, but also partly due to the heterosis advantage of hybrid breeding.  

Table 2. Plant establishment, days to emergence and 100 plant weights (15 days after emergence) for three hybrids (Pioneer 44Y84 (CL), Hyola 50 and Hyola 555TT) and three open pollinated (Pioneer 43C80 (CL), AV-Garnet and ATR-Gem) canola varieties segregated into large and small seed sown at three planting depths.

**Numbers within each section (e.g. Establishment) designated with a different letter are significantly (P=0.05) different.

Starter fertiliser trials

At each trial site in 2012 a phosphorus rate trial was also sown. The phosphorus product used was triple super which does not supply any nitrogen with the phosphorus. The phosphorus rates applied were 0, 5, 10 and 20 kg/ha, with the fertiliser being placed directly with the seed.

There was no effect of phosphorus rate on canola establishment on the cracking clay (Grey Vertosol) soil at Trangie. In contrast, increasing P rate significantly reduced the establishment of all varieties on the lighter textured soils at Nyngan (Red Chromosol) and Coonamble (Brown Chromosol) (Figure 2). All varieties experienced a similar reduction in establishment, regardless of seed size or plant type. 

Grain yield responded positively to phosphorus application at Trangie and Nyngan, which highlighted that the complete exclusion of phosphorus in order to improve crop establishment is not reasonable. 

Two further phosphorus trials were conducted in 2013, with the Trangie trial planted on a lighter textured soil (Red Chromosol) compared with a heavy (Grey Vertosol) soil in 2012. There was a significant establishment reduction at both sites as phosphorus rate (applied as triple super) increased (Figure 3). Further product comparisons at a common P rate showed that all major phosphate fertilisers (MAP, DAP, Single Super, Triple Super, Supreme Z) affected establishment to a similar degree. Despite the effect on establishment, grain yield still responded positively to phosphorus at Nyngan, with the 5 kg/ha P rate yielding 0.25 t/ha more than the nil P treatment but with no further yield increase beyond this rate.

For growers using a tine seeder it is generally possible (and recommended) to separate seed and fertiliser to avoid the negative effects of starter fertiliser. For growers with a disc seeder (or considering a disc seeder), there are several management options available such as:

• Planting on relatively narrow crop rows to reduce fertiliser concentration in the furrow.
• Plant canola early allowing greater root exploration, with potentially less phosphorus application required.
• Pay strict attention to closing devices. The firmer/heavier the closing device, the greater the negative impacts of phosphorus fertiliser.

Conclusion

To maximise grain yield potential canola needs to be planted early. This requires careful attention to detail in relation to crop establishment. Since the soil surface dries out more rapidly in early-mid April compared to mid-May, seed may need to be planted slightly deeper than optimal (up to 5-6 cm deep). In this early planting situation, pay strict attention to seed quality. Sowing large seed (> 5 g/1000 seeds) results in an increased likelihood of achieving an adequate establishment. For growers who wish to purchase seed, hybrid seed is generally larger than open pollinated seed. For growers who retain open-pollinated seed on farm for their own use, aim to clean seed with a 2 mm screen.

Phosphorus is essential for canola growth, but starter fertiliser may have an effect on crop establishment. Avoid high rates of phosphorus in direct contact with canola seed at sowing. Further research is required on phosphorus nutrition of canola, especially on the interactions between P application and sowing time and the effect that liquid phosphorus products may have on canola establishment.  

Contact details

Rohan Bril

Wagga Wagga Agricultural Research Institute

02 6938 198

rohan.brill@dpi.nsw.gov.au