Effects of Variable Rate Nitrogen Application on cv. Barbera Performance: I. Vegetative Growth and Leaf Nutritional Status

Abstract

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 hectares). Then each vigor level was subjected to three fertilization strategies (S) consisting in 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, respectively. Post-trial effects were assessed by taking another NDVI satellite image at the same resolution and by adding a 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 between vigor levels was significantly reduced over year 3 and 4, whereas mean effects related to fertilization strategy were non-significant and very few S × V and S × 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 between vigor levels (CV = 1.42%) vs. standard fertilization at 60 kg/ha (8.20%). A forthcoming companion paper will report about effects on yield, grape health and composition.