Still time to give some canola crops nitrogen boost

Canola growers in low to medium rainfall areas experiencing a good start to the season still have time to apply top-up nitrogen.

Development officer Jack Bucat said crops across the Grainbelt were developing more rapidly than usual, due to early sowing and warm conditions.

Department research, funded by the Grains Research and Development Corporation, had shown that growers in low to medium rainfall areas could apply nitrogen, right up until early flowering.

“This could be good news for growers, especially those who may have missed the traditional pre-bolting timing,” Ms Bucat said.

“Research has shown there is little yield penalty or impact on oil content from delaying top-up nitrogen from the typical timing of six to eight weeks after sowing through to twelve weeks or around the start of flowering.”

The results from 17 trials across the Grainbelt from 2012-14 showed the timing of top-up nitrogen had very little effect on the final crop results.

Ms Bucat said, in general, for the same total rate of applied nitrogen, the time when the fertiliser was applied had very little effect on crop performance.

“For example, in 14 out of 16 trials, a typical nitrogen rate for low rainfall areas of 25-30kg N/ha applied as split applications, top-ups or in one dollop at seeding, four, eight or 12 weeks after seeding produced similar yields and oil,” she said.

“At higher rates of 50kg N/ha, more typically used in medium rainfall areas, similar yields and oils were produced if the nitrogen was applied in splits or top-ups – but oils decreased if all the nitrogen was applied 12 weeks after sowing, which is not a normal practice.

“While we recommend farmers continue with the common strategy of applying nitrogen in the first eight weeks after sowing, these results provide growers with the confidence to delay their decisions until closer to flowering if conditions earlier are uncertain.”

Ms Bucat stressed the recommendations and results pertained to canola crops in low to medium rainfall areas and did not apply to high rainfall areas.

“In higher rainfall areas with higher yield potential, it is important to apply most of the nitrogen by eight weeks after sowing, as growers need to set up reasonable crop biomass and yield potential,” she said.

“Trials are continuing in high rainfall areas to determine if canola continues to respond to nitrogen past 12 weeks after sowing, if conditions remain favourable to increase potential yield.”

To determine the amount of nitrogen to apply, growers should consult their agronomist or use a nitrogen calculator, like the N Broadacre app, to determine the most economic rate.

These tools run specific scenarios for soil types and rotations to determine how much nitrogen is supplied from the soil and the most economic nitrogen rate for a range of target yields.

Ms Bucat said there were two important points to consider when deciding how much top-up nitrogen fertiliser to apply.

“With early and consistent rainfall across much of the Grainbelt, soil mineralisation may have increased nitrogen supply from the soil in many areas,” she said.

“Growers also need to be realistic about their target canola yields and factor in the risk of frost, disease, insect attack and heat stress, which could impact canola crops as the season progresses.”

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