Abstract: Successful biennial raspberry production depends on optimal conditions in all developmental phases during the two years. Adequate vegetative growth with many nodes on the primocanes in the first year will provide many flowering sites, and thereafter, favourable conditions for flower initiation and differentiation will optimize yield potential. A high nitrogen status in plants is however, known to increase the risk of winter injury, and this experience has led to a very restrictive fertilizer practice in field production in the Nordic countries with commonly no fertilizer applications after July 1. Since flower initiation and differentiation, beginning in mid to late august in the raspberry cultivar 'Glen Ample' in Norway, also is influenced by plant mineral nutrient status, the present trials were instigated to compare plant and yield responses when fertigation was terminated in July, interrupted in July/August or continuously applied throughout September. The trials were carried out on long canes of the biennial raspberry cultivar 'Glen Ample' in pots, and in a field trial in polytunnels in Southern Norway. The pots were kept in cold storage at -2°C (±1°C) during winter, while the field trial was grown in ambient winter conditions, comprising a minimum temperature of -26°C. The results from the pot trial showed that shoot height, lateral length and yield were influenced by the fertigation strategies. The field trial involved different fertilizer compositions after a pause in fertigation from July 15 to August 15, and indicates that an interrupted and continuous nutrient supply throughout September gave an earlier bud break compared to a restrictive fertilizer strategy. Interrupted fertigation produced the highest total yield in the potted long canes while berry size showed divergent pattern in the two trials. Interrupted fertigation was in general, positive.
