YIELD AND NITROGEN UPTAKE OF WHITE CABBAGE (BRASSICA OLERACEA VAR. CAPITATA) WITH ORGANIC AND INORGANIC FERTILISERS

To improve fertilisation recommendations in organic farming systems and nitrate vulnerable zones, the response of white cabbage to the application of increasing rates of mineral N (0, 90 and 180 kg ha^-1) fertiliser in combination with increasing rates (0, 20 and 40 t ha^-1) of an organic fertiliser from the composting process (182 days) of the solid fraction (SF) of dairy cattle slurry, was assessed in the summer season in NW Portugal. Cabbage yield was strongly related to mineral N application with an N recovery rate over 70%, but was not associated to SF compost application, except for treatments without mineral N fertilisation where cabbage dry weight increased (P<0.05) from 7.4 t ha^-1 in the control treatment to 9.4 t ha^-1 with the application of 40 t ha^-1 of compost, whilst N uptake increased 64 kg ha^-1. This investigation showed that the SF compost had a high rate of N mineralisation after soil application and that its fertilising effect is related to N availability from mineral fertilisation. Therefore, SF composts may have increased application as a soil fertiliser on low input farming systems such as organic farming.