Nitrogen management strategies in organic winter oilseed rape (Brassica napus L.) production

The efficiency of four different organic fertilisers applied to winter oilseed rape, before (early) or at the beginning of regrowth in spring (normal application time), was studied in two row spacing systems of 12 and 48 cm with inter row hoeing to provide strategies to optimise spring nitrogen (N) fertilisation to organic winter oilseed rape. Six annual field experiments were performed during 2005-2008 in south central Sweden. The following amendments, i.e., Vinass from yeast production, Biofer meat and bone meal, dairy slurry and chicken manure, were applied at a rate corresponding to 100 kg N ha-1. Crop N uptake, seed yield and oil content indicated greater and earlier N availability of Vinass after application compared with the other amendments. Yield increased by 1,300 kg ha-1 at early spring application (27 March) of Vinass and by 700 kg ha-1 when applied at normal application time (18-26 April). The yield increase was 400 kg ha-1 regardless of application time of Biofer, chicken manure and dairy slurry. The substantially greater yield increase in the Vinass application in relation to the other fertilisers demonstrated the yield potential when N is available earlier. The smaller effect on the yield by the other organic amendments indicated that the N release was not synchronised with the crop demand, and available too late during crop development to affect yield or less N was available due to N losses. Consequently, only Vinass can be recommended for spring application. The two row spacing systems tested can both be recommended, since yield levels were similar. © 2013 Springer Science+Business Media Dordrecht.