Effect of post-bloom foliar nitrogen application on vines under two level of soil fertilization in increasing bud fertility of ‘Trebbiano Romagnolo’ (Vitis vinifera L.) vine

In ‘Trebbiano Romagnolo’ grapevines basal bud fertility is usually low and can be related to bud N status. The aim of the present investigation was to evaluate the effect of foliar N application on bud fertility in a mature vineyard subjected to two levels of soil N (39 and 78 kg N ha−1) fertility induced by application of urea. Both the vines at low and high N soil availability were sprayed once with 2.5 kg 15 N ha−1 in pre-bloom and in post-bloom 15N-enriched-ammonium nitrate. Nitrogen soil application increased soil mineral N significantly from June to October, however, with the exception of main shoot axes, the N concentration in the canopy organs (leaves, buds, and bunches) did not respond to the increase of soil fertility. Foliar N applied in June promoted the percentage of NDFF in apical and basal bud and bunch as well, compared with the application made in July. A linear correlation between leaf and basal bud N concentration in 2014 and basal bud fertility (number of inflorescences per shoot) in 2015 was observed indicating a positive effect of sprayed N on bud fruitfulness even when soil N availability is not limiting.