Optimum N rate and timing for semi-dwarf oilseed rape


Optimum N rate and timing for semi-dwarf oilseed rape

P. M. Berry1, S. Clarke2 and S. Roques3

1ADAS High Mowthorpe, Duggleby, Malton, North Yorkshire YO17 8BP
2ADAS Gleadthorpe, Meden Vale, Mansfield, Nottinghamshire NG20 9PF
3ADAS Boxworth, Boxworth, Cambridge, Cambridgeshire CB23 4NN


This project compared a semi-dwarf variety (PR45D03) with a standard height variety (Excalibur) to investigate whether:
i) a semi-dwarf variety has a different economically optimum nitrogen (N) rate and different optimum N timings,
ii) 'Canopy Management' principles apply for a semi-dwarf variety,
iii) there are any differences in the N residues following harvest, and
iv) a semi-dwarf responds differently to a PGR.

Three winter oilseed rape experiments were established in each of the 2008-09 and 2009-10 growing seasons near ADAS sites High Mowthorpe (N. Yorkshire), Rosemaund (Herefordshire) and Terrington (Norfolk). The hybrid varieties PR45D03 and Excalibur were tested at six or seven N rates applied at Conventional or Canopy Management timings, with or without Folicur.

Results showed that, despite being, on average, 33 cm shorter the semi-dwarf variety required the same amount of fertiliser N to achieve optimum yield. Several of the Canopy Management principles were shown to be the same for the semi-dwarf and standard height varieties including; a crop N uptake of 50 kg N/ha to build each unit of green area index (GAI), a similar target optimum GAI at flowering and the same N uptake efficiencies. Shorter stems did not affect the amount of N required to build each unit of GAI because lower stem biomass at flowering was compensated by a greater concentration of N in the stem.

The semi-dwarf variety produced similar sized yields to Excalibur, and by harvest there were no significant differences in the amount of N taken up by the crop and the amount of N taken off in the seed between the variety types. The semi-dwarf variety had an average stem biomass of 3.75 t/ha compared with 4.52 t/ha for Excalibur, and a greater N concentration in the stem and pod wall tissue at two sites. As a result of these counteracting effects both the semi-dwarf and standard height variety left a similar amount of N in crop residues following harvest.

In the one experiment where the canopy following winter exceeded the minimum threshold GAI for using a PGR it was shown that Folicur applied at 1.0 l/ha at the green bud stage significantly increased the yield of the semi-dwarf variety. This indicates that semi-dwarfs will respond positively to PGRs when canopies are large. Folicur was shown to increase seeds/m2 by increasing the amount of light that penetrated through the flowering layer.

Price: £16.17

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