Within-field Variability and Variable Rate Nitrogen Fertilization in a Barbera Vineyard (Italy)

Within-vineyard variability is known to deeply affect vine performance. Precision viticulture (PV) is a precious tool to describe and manage it through innovative variable rate technologies (VRT) that deliver a calibrated input according to the real vine need. Very few comparisons are still available between standard and VRT protocols. The present study aims to: i) describe within-field variability in a vineyard sited in the NW of Italy through a standard NDVI approach; ii) provide agronomical ground truthing on a two year basis (2012-2013) of the NDVI vigor levels; iii) evaluate mid-term effects of VRT-assisted N-supply. A multispectral image by remote sensing was taken on July 2010 (full canopy) on a mature, Guyot trained, cv. Barbera/ K5BB vineyard planted at 4167 vines/ha. Experimental layout was a vigor level x N-supply strategy factorial. Three vigor levels (low-LV, medium-MV and high-HV) were derived from the NDVI map, whereas the N strategy included traditional, VRA (VR application) and control. The N-supply (kg of N/ha) varied as it follows: control (0 kg/ha), traditional (60 kg/ha), VRT (0, 60 and 120 kg/ha in HV, MV and LV vigor blocks, respectively). In HV, pruning weight was higher than LV (895 vs. 485 g/vine), whereas berry and cluster weight and yield decreased from HV to LV (3 vs. 2.3 g, 291 vs. 181 g and 5.9 vs. 3.2 kg/vine, respectively). Cluster rot intensity varied according to compactness (12 vs. 57% and 17.5 vs. 23.5 g/cm in LV and HV, respectively). Total soluble solids, anthocyanins and phenols were higher in LV than HV (24.9 vs. 22 Brix, 1.56 vs. 0.89 g/kg and 2.66 vs. 1.74 g/kg), while malic acid was highest in HV (4.7 g/L). NDVI was closely correlated with pruning weigh, laterals growth, berry weight, cluster compactness and must pH. Vines from LV were most balanced and able to provide the best fruit quality in a context of long-aging red wine production. The VRA reduced N waste in HV while vines from LV blocks showed a low sensitivity to increased N supply.