Assessing the benefits of using foliar N on oilseed rape


Assessing the benefits of using foliar N on oilseed rape

P.M. Berry1 and S. Roques2 1ADAS High Mowthorpe, Duggleby, Malton, North Yorkshire YO17 8BP
2ADAS Boxworth, Boxworth, Cambridge, CB23 4NN

October 2011


The specific objectives of this project were to:
1. understand whether late foliar N gives any yield advantage over and above optimal amounts of soil applied N such as ammonium nitrate.
2. identify the optimum timing and rate of foliar N.
3. quantify the efficiency with which foliar N is used by the crop
4. develop guidelines for the best use of late foliar N.

Field experiments were set up in 2008/09 and 2009/10 near ADAS Rosemaund, Herefordshire, and near ADAS High Mowthorpe, North Yorkshire. Each of the four experiments investigated six rates of soil applied N (ammonium nitrate) ranging from 0 to 280 or 320 kg N/ha with each treatment followed by zero or 40 kg/ha of foliar N applied as Nufol 20 (20% N) at the end of flowering. Each experiment also investigated five rates of foliar N ranging from 0 to 120 kg N/ha and five timings of foliar N from mid-flowering to two weeks after the end of flowering.

Foliar N at 40 kg N/ha increased the gross output by, on average, 0.20 t/ha across all experiments (range of 0 to 0.40 t/ha). This increase in gross output was achieved despite a reduction in the percentage oil content in the seed by an average of 0.9%. The gross output response was the same regardless of whether it followed sub-optimal or super-optimal rates of soil applied N, indicating that foliar N can increase yields over-and-above that achieved from optimal amounts of soil applied N. Similar yield responses were observed for foliar N applications between mid-flowering and two weeks after the end of flowering, which may indicate that foliar N could be combined with a fungicide spray during flowering. A foliar N rate of 40 kg/ha was found to be the maximum rate that should be used. Foliar N was usually taken up with a high efficiency of 70 to 100% and the resulting increase in post-harvest N residues was modest. It is recommended that foliar N should not be applied when the temperature is above 18°C. Yield responses were quite variable and further work is needed to identify environmental and crop factors that cause this variation. If minimal crop damage from applying foliar N is assumed then it may be concluded that, across a number of fields and seasons, applying foliar N at 40 kg N/ha will generally return a profit as long as the ratio of fertiliser cost (£ per kg of elemental N) to oilseed rape price (£/kg) is less than 3.0 when foliar N costs between £0.50 and £0.75 per kg of N, or the cost:price ratio is less than 3.5 when foliar N costs £0.80 to £1.00 per kg of N.

HGCA Project Number: 3507
Price: £9.17

Related Publications

Document downloads

View printer friendly versions of these publications

Download this publication PDF

PR481 - Summary.pdf

File size: 94KB
Download this publication PDF


File size: 218KB