May 14, 2014
Well-structured crops could profit from late foliar nitrogen
Extra late nitrogen could be particularly valuable in making the most of some of the best structured winter oilseed rape canopies, ADAS specialist Dr Pete Berry has seen in recent years.
Speaking to more than 100 growers and agronomists attending the AgriiFocus OSR Day at Aldbourne near Marlborough, he pointed out that around 40 kg/ha of foliar N applied at the end of flowering has given an average yield response of over 0.3 t/ha in a total of 23 ADAS and other trials he has assessed to date. And this following optimum inputs of soil-applied N for both canopies and yield.
“Oil is formed relatively late in seed fill,” he explained. “So anything that can be done to prolong seed filling will lift oil production at harvest, providing the canopy is actively photosynthesising and capturing sufficient light.
“Active photosynthesis during seed fill is, of course, essential to seed yield too because, unlike cereals, oilseed rape does not mobilise carbohydrate from the stem to support the developing seed. However, the seed does extract nitrogen from the pod walls. This makes late N valuable in providing sufficient nutrition to allow the seeds to grow without unduly hastening pod senescence.”
Dr Berry warned, however, that the value of late foliar nitrogen varies widely with crop condition and circumstances. Across 11 ADAS trials, indeed, gross output responses have ranged from zero to over 0.4 t/ha.
High temperatures (more than 19oC) at the time of application are known to limit the crop’s response to late foliar N while crops which have had sub-optimal soil applied N are expected to respond more strongly to late foliar N. It is also possible that good canopy structure and yield potential are important factors in the equation.
“We know that open, well-branched canopies with plenty of photosynthesising lower leaves and pods are the secret to high seed numbers and good seed fill,” he stressed at the event. “They allow sunlight to penetrate much better below the upper layers than dense canopies of thin plants.
“The optimal 20-30 plant/m2 populations with excellent primary and secondary branching we’re seeing in far more crops than usual this season leaves them well-placed to make the most of whatever the summer brings. A combination of appropriate seed rates, the open autumn and good plant growth regulation also means they are generally well-rooted with good access to the available soil moisture.
“These types of crops with high yield potential may well be good candidates for late foliar nitrogen because they will need a good supply of late N to realise their high yield potential” said Dr Berry. “The value of applications will, of course, also depend an assessment of all the costs involved – including any reduced oil percentages and additional application expenses – as well as seed values. So I would urge growers and their agronomists to assess their particular crops and circumstances as soon as possible if they wish to take advantage of what could be an excellent opportunity for many.”