Article taken from Crops Magazine
By Richard Allison
Only 10% of growers generally opt for a flowering application of nitrogen, but this season crops are likely to have a greater need for late nitrogen. Yara agronomist Ian Matts says there is a wide range in plant size, including very forward crops that had a green area index of 3.0 in late January. “Big crops mean growers will end up with bigger canopies than desired, even after using a growth regulator, making nitrogen application timing more critical this season.” This is because larger canopies will need maintaining during seed fill to avoid pods being aborted, which is where a flowering application comes in.
NITROGEN STRATEGY
Mr Matts explains that there are two different applications with different roles: the first, which goes on in two splits, is to build up the canopy; then the second maintains the green canopy to build yields. The first split has gone on for Get extra 0.4t/ha rapeseed yield with flowering spray many and big crops enabled farmers to cut back on their fertiliser, as a crop with a green area index of 3.0 already has 150kg/ha of nitrogen. Agrovista’s Chris Martin says: “You don’t want too much early nitrogen to overcook the canopy, as more often than not, crops have too thick a canopy.”
WHY OPT FOR FLOWERING DOSE?
But this year, both Mr Matts and Mr Martin agree there is a greater case for an additional flowering application to keep the canopy greener for longer. Mr Matts explains that leaves start to senesce mid-flowering – therefore, there is a need to keep this leaf material photosynthesising to feed the seeds. “This is because if seed starts stripping seed walls for nitrogen too early, you get early pod senescence and lose seeds, which means lower yields,” he says.
HOW MUCH?
A flowering application is just a small top up of 40-60kg of N/ha, which can be added to the sclerotinia tank mix. If the earlier application was lower because of a large GAI, Mr Matts advises applying nearer the upper figure of 60kg N/ha. Farmers should avoid applying on a hot day to minimise scorch risk, says Mr Matts. “You don’t want to be applying to a stressed crop in hot conditions; it is better to apply in the cooler evening.”
YIELD RESPONSE
A three-year trial in Scotland found a consistent yield increase of 0.45t/ha in each year. Typically growers have seen 0.3-0.4t/ha, but this year may see a bigger response as there is a larger canopy to maintain. Mr Martin has seen trials that have consistently shown a 0.3-0.4t/ha yield benefit to late nitrogen. He is a fan of late nitrogen and it was part of the successful strategy used by North Yorkshire grower Steve Tuer on the unofficial record crop. His Incentive OSR achieved 7.2t/ha last summer. But despite the clear benefits, only 10% of growers routinely apply a flowering application.
LIMITED UPTAKE
Both believe uptake is being hampered because the original message was to apply at late flowering and growers did not want to go through the crop with an additional spray. So back in 2013, several companies including Yara and Agrovista and ADAS took part in a four-year Innovate UK co-funded project taking another look at timings and rates of foliar nitrogen. It concluded that there was no difference between early, mid or late flowering. The conclusion was that it could be applied any time during flowering. However, Mr Matts says the findings coincided with a poor year for oilseed rape (2013) and farmers cut back on spending. “They were already applying more nitrogen fertiliser, as crops were small, so it didn’t catch on.” Mr Martin adds that there was also a concern that a late application of foliar nitrogen on the pods reduced oil content. But he hasn’t seen any evidence of this with the earlier mid-flowering application. However, you do see a response and this season it could be even greater as these big crops may run out of steam early on, says Mr Matts. Brixworth Farming, which farms 2,000ha in north Northamptonshire used this approach in three of the past five years. Mr Matts, who does the agronomy, says a Yara trial last year showed a response and he believes it helped them hit target yield of 4.5t/ha last summer. While liquid is the best approach with the sclerotinia tank mix, Mr Martin says benefits can also be achieved by applying late nitrogen in granular form. He advises leaving it as late as possible to get an even spread, but warns there is a risk of poorer uptake in dry conditions. He adds that soils may also be depleted by the high yields last summer, combined with the wet winter so soil levels maybe lower. “Crops may, therefore, need a bit more nitrogen later on.”