High potential of variable rate fertilization combined with a controlled released nitrogen form at affecting cv. Barbera vines behavior

Variable rate technologies allow site-specific management of parcels characterized by different levels of vigor and/or yield. Fertilization based on actual plant needs is one of the most promising applications of precision farming aiming at improving efficiency, optimizing vine balance, as well as limiting environmental impact. Although this strategy appears suitable for developing new vineyard management models, few experiences validating this hypothesis are available in the literature. Based on a pre-trial remotely sensed vigor map (NDVI-derived, 5 m resolution), a three-year study was performed in a Vitis vinifera L. cv. Barbera vineyard situated in the Colli Piacentini area. Vigor level (L = low, M = medium and H = high) and fertilization technique (Standard, Variable Rate Application, and unfertilized Control) were the main factors in a randomized block design. The controlled release fertilizer Multicote™ Agri ([NPK fertilizer 13-5-21 + 7MgO+14SO3 (Controlled Release Nitrogen >46% on the total nitrogen, with longevity 2÷4 months), low in chloride] was used and the input rate calculated according to the N-supply. For each vigor level the study compared no fertilization (0 kg/ha), standard supply (40 kg of N /ha) and Variable Rate Application (VRA) supply delivering 0, 40 and 80 kg of N/ha to H, M and L, respectively. Vine growth, yield, leaf nutritional status and fruit composition were assessed. Results show that the classified L vigor plots had significantly less growth (i.e leaf area or pruning weight per vine) than M and H vigor plots, whereas yield components and grape composition followed a linear variation with vigor. There was a large prevalence of vigor x technique interactions suggesting that VRA had a differential impact on vine behavior depending upon the initial level of vigor. For vegetative and yield parameters, in the L vigor vines, increased Multicote™ Agri dosage delivered as control (0 kg of N/ha), standard (40 kg of N/ha) and VRA (80 kg of N/ha) caused a very close and linear increase in total leaf and yield per vine, whereas, within the M and H vigor plots, the effect due to fertilization technique was very mild. Such a behavior was nicely mirrored by grape composition at harvest as, in L vines, applying 40 or 80 kg of N in the form of Multicote™ Agri induced a progressive and significant reduction in both must soluble solids and total anthocyanins concentration, although the oenological quality of the resulting must was still satisfactory and in compliance with the oenological target. The novelty of the present work is that, unlike previous variable rate fertilization attempts where a rapid nitrogen release fertilizer such as urea was used, L vigor vines showed a very prompt response to the amount of Multicote™ Agri application, confirming higher effectiveness of this chemical form and higher flexibility in adjusting the level of vigor and yield according to specific needs. Conversely, when the initial level of vigor was medium or high, differential fertilization resulted in overall minor modifications of the vine behavior.