Oilseed Rape Management

Evaluating the effect of different nitrogen strategies on the yield of modern oilseed rape varieties

This study reports experiments funded by GrowHow, HGCA and Bayer Crop Science to investigate the optimum N strategy for two modern high yielding varieties. The 'high biomass' variety Winner and 'low biomass' variety Castille were grown at three sites using a range of N rates (0 to 360 kg/ha) applied either at conventional or managed timings. Managed timings involved applying sufficient early N to achieve the optimum canopy size at flowering (GAI = 3.5) and varying amounts of late N at early flowering. This involved omitting, or severely reducing, the amount of N applied at the conventional first split timing. Each treatment combination was treated with and without Folicur applied during stem extension. The specific objectives included;

  1. To investigate N management strategies that help achieve the high yield potential of new oilseed rape varieties.

  2. To investigate the interaction between N rate, N timing and Folicur on yield and margin over fertiliser and Folicur cost.

The economically optimum N rates were 74 kg N/ha at Boxworth, 238 kg N/ha at High Mowthorpe and 223 kg N/ha at Rosemaund. These were not altered by variety, N timing or Folicur. Yield and margin was generally increased by delaying the N applications when the SNS (soil and crop nitrogen supply) was moderate or high. This was the case for Winner at ADAS Boxworth and Rosemaund where the SNS was 123 kg/ha and 93 kg/ha respectively. Avoiding the first split and applying the bulk of the N fertiliser at what would normally be considered the 2nd split timing followed by a smaller amount two to four weeks later increased yield at Boxworth and Rosemaund by 0.37 t/ha and 0.15 t/ha respectively and increased margin after accounting for oil content by £26/ha and £27/ha respectively. Delaying N significantly reduced lodging in Winner at these two sites and it seems likely that this contributed to yield benefits. Delaying N at these sites increased the yield of Castille by 0.1 t/ha at Boxworth and had no effect at Rosemaund. Little or no lodging was observed in this variety which may explain the smaller effects. At High Mowthorpe the SNS was just 67 kg/ha and delaying N had no effect on Winner and slightly reduced the yield of Castille. It is likely that a greater proportion of N should be applied at the first split timing if the SNS is small. It was shown that more late N is required at sites with a greater yield potential. However, current assumptions of an additional 30 kg N/ha for each 0.5 t/ha of yield potential greater than 3.5 t/ha may be underestimating this requirement.

Delaying N applications did not affect the oil content of crops fertilised at the optimum rate at either High Mowthorpe or Rosemaund. However delaying N at Boxworth reduced oil content at the 120 and 240 kg/ha N rates. The most likely reason for this was that the final application was made too late for the crop to take it up efficiently. At Boxworth the final N application was at mid flowering compared with early flowering at the other two sites. It was shown that this caused premature senescence of the pod canopy. Nonetheless the increase in yield for Winner from delaying N more than compensated for the reduction in oil /content.

Managed N timings resulted in greater N uptake by the crop at the two sites where it caused a yield increase. There was a trend for the Managed N timings to reduce stem biomass, but the amount of N in the stem and pod walls after harvest was unaffected.

It is likely that the N residues following harvest were smaller for the Managed N treatments that increased yield due to the greater amount of N taken off in the seed.

Across all sites Folicur applied at green bud increased the margins at optimum N by between £4/ha and £24/ha. Folicur tended to increase yield more at high N rates or when N was applied at Conventional timings. It is likely that at least part of the yield improvements caused by Folicur resulted from a reduction in stem height and lodging risk.

Full experiment report:

Oilseed Rape Managmenet final report    (307kb)

Graphs, pictures and tables of the research results:

Oilseed Rape management    (8027kb)