Sultana fruitfulness and yield: responses to rootstock and nitrogen supply

Abstract

Nitrogen supply to irrigated Sultana grapevines on own roots or on Ramsey rootstock was varied in a field trial conducted at Irymple, north-western Victoria, over 3 seasons. The nitrogen treatments imposed were 0, 40 and 80 kg N/ha.year supplied in 4 equal applications (2 pre-flowering — late September and mid-October; 1 post-flowering — mid-November; 1 post-harvest — late February) Yields of dried vine fruit were responsive to both nitrogen supply and rootstock. Despite lower bud fertility, Sultana on Ramsey rootstock out-yielded Sultana on own roots due to greater numbers of 1-year-old canes suitable as bearers, more berries per bunch and larger berries. Yield of Sultana on own roots responded in a similar manner to increasing nitrogen supply as yield of Sultana on Ramsey rootstock. Yield increases were due to improved bearing potential (more suitable bearers) and more berries per bunch when nitrogen supply increased from 0 to 40 kg N/ha.year. When nitrogen supply was raised from 40 to 80 kg N/ha.year, a further yield increase was due to enhanced bud fertility and larger berries. These yield components behaved differently for Sultana on own roots compared with Sultana on Ramsey rootstock, but, overall, balanced out such that final yield was not affected by rootstock. Consequently, rootstock was not a significant factor in the dried vine fruit yield response of Sultana to nitrogen supply.