Rohan Brill (left) and Karl Moore (NSW DPI technical officer) checking canola trials before harvest.
PHOTO: Bob Freebairn
- Hybrid canola varieties yielded 36 per cent more than open-pollinated varieties in a two-year northern NSW GRDC-funded research project that involved 24 experiments
- Large-seeded hybrids tended to establish better than open-pollinated varieties when sown deeper than normal, a common requirement in northern NSW and Queensland
- Plant populations of about 20 plants per square metre were generally optimum for all varieties and seasonal conditions
Trial sites included Coonamble, Nyngan, Trangie, Moree, Blackville, Caroona, Garah, Mullaley, Spicers Creek and Gilgandra. These represented a range of soil types, from sandy loam to heavy vertosol, and climatic conditions, from low rainfall to medium-to-high rainfall.
Variety type yield differences were the highlight feature of the GRDC-supported Variety Specific Agronomy Packages (VSAP) study. The study examined the interaction between variety choice and various agronomic practices, including sowing rate, sowing depth, and phosphorus and nitrogen nutrition, and the impact on yield and quality.
Rohan Brill, from the NSW Department of Primary Industries (DPI) Wagga Wagga Agricultural Institute, led the study. Also involved were Matthew Gardner, from AMPS Agribusiness, Tamworth (formerly NSW DPI), Leigh Jenkins, from NSW DPI Trangie, and NSW DPI Tamworth-based Stephen Morphett, Rod Bambach and Bruce Haigh.
Averaged across all sites and seasons, the hybrid entries yielded 0.4 tonnes per hectare more than open-pollinated varieties: 1.5t/ha compared with 1.1t/ha. This 36 per cent yield advantage represents a substantial gain in profitability, even with higher seed costs.
Triazine-tolerant (TT) varieties were also generally lower yielding than non-TT varieties; however, hybrid TT varieties maintained a consistent advantage over open-pollinated TT varieties.
The advantage of hybrids was most pronounced in the more western environments and where the majority of the grain yield was derived from moisture stored prior to sowing.
Of the 24 experiments there was little evidence for the need to manage hybrid canola varieties differently to open-pollinated varieties.
The main exception was within the seeding-depth experiments (Figure 1), where genotypes with larger seed (usually hybrids) generally showed less yield reduction than smaller-seeded varieties when sown deep.
For example, at Nyngan in 2013, a small-seeded open-pollinated variety had a reduced yield of 1.3t/ha where seeding depth increased from 25 to 75 millimetres. However, there was no significant yield reduction in the large-seeded hybrid variety because it was able to maintain acceptable establishment rates despite the deeper sowing.
Figure 1 The effect of seeding depth on the grain yield of six canola varieties at Nyngan in 2013
The ability to establish plants adequately from relatively deep sowing is important for being able to sow at optimum dates. Soil is often dry on the surface but placing the seed deeper into residual summer moisture will improve the likelihood of establishing a canola crop on time.
Grain yield response to nitrogen application was positive in all experiments and was not reduced by high nitrogen application (up to 120 kilograms/ha nitrogen) in any experiment.
The application of nitrogen often reduced oil concentration; however, was more than compensated for by the extra grain yield.
Mr Brill says the data supports the view that nitrogen management of newer hybrid canola varieties does not need to differ significantly from management of open-pollinated types.
The research showed grain yield generally responded positively to increasing plant population, up to 20 plants per square metre, regardless of variety type (Figure 2).
Overall there was no further yield increase with further increases in plant population. This suggests target populations for newer hybrid varieties are similar to open-pollinated varieties.
There are often complications in converting a target plant population to a sowing rate as hybrid varieties have fewer seeds per kilogram (which means the same number of seeds will weigh more); however, they often have a higher establishment rate so less seeds need to be sown.
A further advantage of canola varieties with superior seedling vigour, such as most hybrids, is their greater ability to suppress weeds and to yield higher in weedy situations.
Figure 2 Grain yield response of four canola varieties to five plant populations at Nyngan in 2013.
Results detailed in a paper, ‘Competitive ability of Australian canola (Brassica napus) genotypes for weed management’, published in November 2014 in Crop & Pasture Science, found weed biomass at flowering was generally reduced by 50 per cent more in the presence of the strongly competitive genotypes than the least competitive. This means lower weed-seed production and reduced seedbank replenishment.
Significant differences in canola grain yield were recorded between weedy and weed-free plots, depending on crop genotype, presence of weeds and season.
For example, crop yield tolerance to weed competition (where 0 per cent equals no tolerance and 100 per cent equals complete tolerance as far as yield reduction is concerned) in a dry year with a heavy ryegrass population ranged from 0 per cent for a poor-seedling-vigour, open-pollinated variety to 30 to 40 per cent for a high-seedling-vigour hybrid.
The weeds study was undertaken by Professor Deirdre Lemerle, from the Graham Centre for Agricultural Innovation (an alliance between Charles Sturt University and the NSW DPI), and David Luckett, Peter Lockley, Eric Koetz and Hanwen Wu, from the NSW DPI Wagga Wagga Agricultural Institute. The researchers all work on several related GRDC-funded projects.
Professor Lemerle noted that competitive crops are a low-cost tactic for integrated weed management to reduce dependence on herbicides and retard the spread of herbicide-resistant weeds.
Further details of Mr Brill’s research can be found in a paper titled ‘Effect of genotype choice and agronomic management on canola performance in Northern NSW – 2012 and 2013’ presented at the recent Australian Research Assembly on Brassicas conference.
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