The majority of canola growers are now highly experienced in agronomy and work with farm advisors and agronomists on ‘as need’ basis. However from time to time it is useful to get back to basics to check you are doing all you can to maximise yield. Don’t forget why we are growing canola in 2017 when the world is well supplied with wheat; we grow canola to make money and naturally, to supply a well sought-after commodity.
When it comes to variety selection, select a variety with the best package of yield, oil, maturity to suit and disease resistance available. Plant breeders continue to be focused on bringing better products to market. Remember, they have thousands of plots in the ground for evaluation so that you can choose one or two of the best. Look at proven performers over two seasons by comparing not just across location but when grown in a similar location to your farm on www.nvtonline.com.au
With paddock selection, there are a number of attributes to consider. There is the overall soil health including soil pH, soil structure and fertility, the timing of the crop in the rotation, the herbicides used in the previous year and plant-back periods, also remember the weed seedbank history.
Canola-growers experienced a wetter season across the cropping regions of Southern and Western Australia in 2016. The impact of this wetter season now poses some challenges when planning for this year’s crop.
While canola is a small seed we know that great soil structure is better for the oxygen levels in soil, the infiltration of water, soil biology, and healthy root growth. Canola is tap-rooted and roots will commonly explore down to 1.5-2.0 metres.
Sodic soils are dispersive, meaning they repel the take-up of water. They literally get wetter, because the water sits on top and cannot penetrate the profile, or they get drier. The water on top never has a chance to infiltrate so it evaporates more quickly meaning it isn’t there for the crop to access.
These sodic soils require fixing or amelioration before even considering canola. An uneven plant population is worse than a low plant population with canola. An input like gypsum to ameliorate the sodic soil also requires soil moisture to start working, usually the first 50mm in a season, so it makes sense to apply it well before the autumn break. Animal manures can supply organic matter and nutrients at low levels and can also help to ameliorate the soil from sodicity (high exchangeable Sodium > 5%). Mechanical amelioration may be required in severe situations.
Nitrogen, Phosphorus and Sulphur are the top 3 nutrients required by canola. While residual organic nitrogen can supply some of the crop’s Nitrogen requirements, additional nitrogen fertiliser will be needed to maximise yield potential. Early nitrogen intervention is critical to achieving yield potential through accumulation of biomass between emergence and 4-6 leaf. Research results further support this as shown in chart 1.
Chart 1. 2016 Pioneer time of sowing trials, Yield: NDVI (Early Biomass) Correlation.
Canola is not as efficient at recovering soil Nitrogen from the ground as a wheat plant, (Laura Watson, CSIRO, February 2017, GRDC Soil and Plant Nutrition Workshop, Griffith) so it does yield more where there is surplus Nitrogen to its crop requirements.
Monitor the health of the crop throughout all crop stages and be responsive to meeting the crop needs dependent on seasonal conditions.
Consider what happened the year before. If paddocks were waterlogged, it is likely that denitrification of nitrogen occurred in anaerobic conditions and leaching and run-off events were also likely. These events coupled with increase yields in many environments meant an exit of Nitrogen from the system. However, with a wet spring, soils with reasonable to good organic matter are likely to have mineralised nitrogen in warm, wet conditions. Soils lower in organic matter will have been more reliant on top-dressed Nitrogen to meet crop needs, but many growers were challenged to apply Nitrogen with supply and paddock trafficability issues.
We are always balancing the supply of Nitrogen and the supply of soil water in a rain-fed situation. They are both essential and when we have one without the other, the crop experiences stress and growth slows or comes to a halt.
Many cropping soils have adequate levels of Phosphorus in the soil-bank and for most soil types this benchmark is above 30-35 Colwell P. Early Phosphorous is essential for setting yield potential and growth under cold conditions.
Canola does need Sulphur (S) but it doesn’t require as much as originally thought, using approximately 3.0 kg/ha per tonne of canola. An application of 400-500 kg/ha Gypsum to a paddock will often supply enough Sulphur for 3 high-yielding canola crops, allowing for some movement and loss in the paddock. If unsure about Sulphur levels then get this nutrient tested along with your deep N test. Sulphur is mobile and it may be sitting down further in the soil profile.
Article produced by –
Rob Wilson, Canola Market Development Manager – GenTech Seeds
Lisa Castleman, Senior Land Services Officer – Riverina Local Land Services