Alberto Vercesi

An Improved Multichamber Gas Exchange System for Determining Whole-Canopy Water-Use Efficiency in Grapevine

A multichamber whole-canopy gas exchange system coupled with an automatic pot weighing device was tested for continuous 24 hr recording over 50 days in a trial comparing cv. Sangiovese vines subjected to progressive reduction of total transpiration water supply to well-watered vines. The system ran smoothly under regular maintenance for the entire period and gravimetric vine water loss was highly correlated with chamber-derived vine transpiration (r = 0.95) for data pooled over treatments. Seasonal and diurnal whole-canopy net CO2 exchange rate (NCER) and transpiration (Tc) showed that supplying 50% and 30% of daily gravimetric vine water loss (Tg) consistently corresponded to a NCER more than proportionally limited as compared to Tc, hence leading to lower canopy water-use efficiency (WUE) expressed as NCER/Tc ratio. Conversely, canopy WUE did not differ between treatments at 70% Tg restitution and rewatering. Similarly, during the most limiting water supply periods, the WUE difference between treatments was greatly reduced during cloudy days with lower vapor pressure deficit and higher diffuse-to-direct light intensity ratio. Data sets taken over different time frames on whole-canopy WUE provide a scenario different from that which might derive from traditional single-leaf assessment, reporting in almost all cases that intrinsic WUE increases under stress and suggests that the methodology used can mask or alter conclusions about adaptive response of grapevine cultivars to water stress.

Effects of Early Shoot Trimming of Varying Severity on Single High-Wire Trellised Pinot noir Grapevines

Amid growing concerns over global warming and available management strategies to reduce cluster temperature and prevent overheating and sunburn damage, there is increasing interest in sprawling, nonpositioned canopies as an alternative to traditional vertically positioned ones. However, management of sprawling canopies requires adjustments to maintain a mostly erect growth pattern during the season. A three-year study (2009–2011) was carried out to investigate the performance of 15-year-old Pinot noir grapevines trained to a single high-wire trellis subjected to prebloom shoot trimming to retain seven (T7) or eleven (T11) main stem leaves. There were significant year × treatment interactions: with a low crop and weather conducive to posttrimming lateral regrowth in 2010, trimmed vines had higher leaf area, soluble solids concentration, pH, total anthocyanins, and cluster rot incidence than control vines, whereas in 2009 and 2011, the overall must compositional pattern was reversed due to suboptimal leaf-to-fruit ratios in the trimmed plots. The effects linked to this necessary operation are highly dependent on unpredictable weather occurring after shoot trimming; hence, the milder trimming severity (T11) may more successfully balance the need to induce a still mostly erect canopy while retaining sufficient vine leaves to buffer possible weak lateral formation after trimming. This paper provides new and useful knowledge for improved canopy management in trellises with free shoot growth due to the absence of foliage wires.

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 × 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 among vigor levels (CV = 1.42%) versus standard fertilization at 60 kg/ha (8.20%).