Applying foliar nitrogen towards the end of flowering keeps the crop green for longer. This maintains an efficient green leaf and pod canopy to sustain photosynthesis and produce carbohydrates during the important seed fill stage; therefore creating more yield potential.
There are three key stages when nitrogen should be applied to oilseed rape – autumn for the optimal establishment, spring for optimum canopy structure and growth before flowering and during flowering to optimise the green area duration – thereby maximising yields.
Maintaining the green area index important in oilseeds
Plants need an adequate supply of carbohydrate late on in the season to prevent pods and seeds from aborting, reducing yield. Unlike in cereals, where plant reserves are remobilised, oilseed crops rely mainly on current carbohydrate production during this period to meet the demand, therefore plants need to continue photosynthesising efficiently late into the season. Pods are a less efficient source for this purpose than leaves, therefore it is important to retain leaves for as long as possible (increasing the green area duration). To achieve this crops require an adequate supply of nitrogen later in the season, which the soil alone may not be capable of supplying.
Keeping the crop greener for longer means that it is able to intercept more light (energy) which, via photosynthesis, it can use to ‘fuel’ pod fill and therefore create yield. Light is intercepted by the green parts of plants, this includes the green pods too once flowering has finished. So by maintaining the green parts of the plant you are effectively extending the period where the crop can turn energy into yield.
An extra 25 tonnes from 100 hectares
Foliar nitrogen is an effective method of maintaining the GAD and there are a few options to choose from to suit each grower’s individual needs.
Foliar urea in the form of Chafer Nufol is a popular option that typically gives an extra 0.25t/ha yield (worth over £75/ha) from 200l/ha application at the end of flowering. Almost 30 trials were previously reviewed by ADAS and showed that by applying late foliar nitrogen there was an average yield increase of 0.25t/ha; with some trials showing an increase of up to 0.7t/ha. The extra 0.25t/ha gives a return on investment of around 2:1.
If foliar urea is not for you, some other options for foliar nitrogen are YaraVita Safe-N 300 which, again, is applied at the end of flowering or YaraVita CropLift Pro (applied at the same timing). YaraVita CropLift Pro also contains a vast range of other nutrients, both macro and micro, to give the crop a boost. This could be particularly beneficial in difficult seasons due to abiotic stresses on the crop such as cold periods or low levels of rainfall.
Trials conducted in 2020 showed average yield increases of 0.35t/ha from an application Safe-N and 0.33t/ha from the application of CropLift Pro, both at the end of flowering.
It is also possible to tank mix foliar nitrogen with sclerotinia sprays and therefore help towards application costs. Chafer Nufol, YaraVita CropLift Pro and YaraVita Safe-N 300 can all be tank-mixed with most fungicides but check physical compatibility with the Yara TankmixIT app.
The optimum rate for foliar nitrogen applied at flowering is 50kgN/ha, but remember, it is important to ensure that your total nitrogen applied does not exceed the N max limit.
Also if applying liquid fertiliser, make sure you don’t apply nitrogen in hot conditions (above 17 degrees) as trials have shown a negative yield response under these circumstances. Early morning or evening are the best times of day to apply liquid fertiliser.
The following fertilisers are recommended for foliar application to oilseed rape
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