Effects of variable rate nitrogen application on cv. Barbera performance: vegetative growth and leaf nutritional status

Variable rate application of vineyard inputs in field parcels characterized by different levels of vigor and/or yield is one of the most promising applications of precision agriculture. In a four-year study, we provided ground-truthing of three different vigor levels (L = low, M = medium, and H = high) derived pre-trial from Normalized Difference Vegetation Index (NDVI) values determined by remotely sensed imagery (5 m pixel resolution) in a small Barbera vineyard (0.64 ha). Each vigor level was subjected to three fertilization strategies (S) consisting of no N supply (C, 0 kg/ha), standard supply (S, 60 kg/ha), and variable-rate application (VRA) delivering 0, 60, and 120 kg/ha to H, M, and L vines, respectively. Post-trial effects were assessed by taking another NDVI satellite image at the same resolution and by adding proximal sensing performed with the MECS-VINE sensor yielding the estimation of a canopy index (CI). Ground-truthing was based on recording main vine growth parameters and leaf nutritional status. Results show that vine balance of L vines was optimal. Variability among vigor levels was significantly reduced in years 3 and 4, while mean effects related to fertilization strategy were not significant and very few S x V and S x Y interactions were found. However, when the ground-truthing assessment was compared with the CI index values, it was very clear that VRA was able to reduce variability among vigor levels (CV = 1.42%) versus standard fertilization at 60 kg/ha (8.20%).