Nitrogen Sink-Source Relations of Three Cauliflower Cultivars.

It is not well understood how high nutritional cauliflower (Brassica oleracea var. botrytis ) achieves its high protein levels and the hearty structure. A study of cauliflower plant nitrogen sink/source relations was conducted in Annapolis Valley, Nova Scotia in 2007. The objectives were to examine cauliflower head quality in relation to N movement from sources (leaf-stems) to sinks (heads) among different cultivars. The treatments consisted of three cauliflower varieties (‘Minuteman’, ‘Sevilla’ and ‘Whistler’) and three shoot-tip straightened rates of N (0, 45 and 90 kg ha^-1), arranged in a split-block design in a commercial production field. Results showed that cauliflower plant source N accumulation was highly variable (3.9-8.2 g plant^-1), depending on the varieties and N rates. Cauliflower source N accumulation peaked at shoot-tip bowed stage. Cauliflower sink N increased rapidly from curd initiation to reach 30% (2.5 g head^-1) of the total N uptake at harvest. The variety and N treatment interaction was significant for ‘Minuteman’ and ‘Sevilla’ at the 45 kg ha^-1 level on sink/source N (P < 0.05). Correlations between cauliflower source N, sink N, head size and whole plant N uptake were significant (0.76 < r < 0.89, P < 0.05). The cultivars ‘Sevilla’ and ‘Minuteman’ had a significantly higher ability of N assimilation than ‘Whistler’ (P < 0.05). It was suggested that the reduced N rate (45 kg ha^-1) at shoot-tip straightened stage could increase the N temporal reserves in leaves and stems to enhance cauliflower plant sink N accumulation and head development.