Nitrogen supply phasing increases broccoli (Brassica oleracea var. italica) growth and yield

Current practice for greenhouse broccoli production is to fertigate with N at a constant rate. Because crop N demands differ according to growth stage, constant N fertilisation under- or over-supplies N at some stages. Nitrogen phasing, whereby successive, different levels of nitrogen are applied, was examined in the two broccoli cultivars Arcadia and Windsor. Two fertiliser levels (150 or 250 mg L-1) and three N rate switching times of one N rate to the other (when 60, 75 or 100% of the growth cycle had been completed) were factorially combined. A growth-stages-fitness-effect (GSFE) was computed, made up of a phase effect and a rate effect. The results showed that dry matter production and yield increased by 10% and 69%, respectively, when N rate was switched from 250 mg L-1 to 150 mg L-1 at inflorescence initiation, compared with the conventional constant N fertilisation rate of 250 mg L-1.