Applying foliar nitrogen during 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 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.
An extra 25 tonnes from 100 hectares
Foliar urea in the form of Chafer Nufol is a popular option which 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 then there is YaraVita Safe-N 300 (liquid) which, again, is applied at the end of flowering.
YaraVita CropLift Pro is another option for late foliar nitrogen on OSR. It also contains a vast range of other nutrients, both macro and micro, to give the crop a boost.
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 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 esceed 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