Defending vineyards: anti-freeze, emergency and climate control irrigation

Introduction
The wine sector is increasingly affected by the effects of climate change, pushing producers to adopt innovative and sustainable strategies to cope with increasingly frequent adverse events. A prime example is particularly hot summers that result in excessive acceleration in grape ripening resulting in an imbalance between technological, polyphenolic and aromatic ripening. In addition, the combined effect of high temperatures and high light radiation is capable of scalding the clusters resulting in a negative effect on grape quality and quantity. Another phenomenon related to climate change is that of late spring frosts: mild winters lead to early vegetative awakenings that expose buds to a higher risk of frost that can compromise the entire production.

This is the context in which the SOS-VIGNE, funded by the Emilia-Romagna Region, operates, setting itself the goal of realizing, testing and popularizing a newly designed multi-purpose irrigation system, inspired by criteria of reduced water and energy consumption, suitable for the prevention of three main climatic adversities in the vineyard: late frost, overheating and burning of the bunches, and water stress. The irrigation system was built by Irrigazione Veneta S.R.L., with automation provided by Giona S.R.L. Research activities were conducted by the Catholic University of the Sacred Heart at the Agricultural Company Cantina Colle del Podio S.S whose vineyards are already equipped with a microaspersion irrigation system.

Anti-brine irrigation
Antibrine irrigation represents an effective solution to counter late frosts, events characterized by a high degree of unpredictability. This type of irrigation is based on the physical phenomenon of latent heat release during the state transition of water from liquid to solid. In other words, the water delivered by the system freezes forming a protective layer around the shoot releasing energy in the form of heat that can protect plant structures sensitive to critical temperatures. It should be remembered, in this regard, that temperatures below 1.5 to 2.0 °C are capable of severely damaging organs now in active growth (swollen bud and later stages). Factors that can determine the effectiveness of this operation are the irrigation volume used, air temperature and dew point at the time of irrigation.

Emergency irrigation
The need for a traditional irrigation supply in a climate change context is related to a high evaporative demand from the atmosphere that may or may not also be associated with soil water shortage. This demand becomes progressively higher with increasing air temperature values and decreasing relative humidity values. In addition, a rational relief irrigation plan must always take into account soil texture, water retention capacity, water infiltration rate, and the possible presence of a turf sward, which always exerts a certain water-competitive action against the vine.

Climate-regulating irrigation
Overheating and bunch sunburn are constantly increasing problems, especially in viticultural areas characterized by warm, temperate climates. High temperatures between 42 and 49 °C can cause significant damage to grapes, which are capable of overheating up to 10-15 °C above the ambient temperature. The degree of intensity of a scald depends on various factors that include cluster size, shape, growth stage and firmness, grape variety, skin thickness, wind speed and plant water status. The interaction of high temperatures, intense light radiation and low relative humidity can cause significant overheating of berries, limiting heat loss through transpiration and consequently increasing the risk of scald damage.

Necrosis of berry tissue is not the first symptom of sunburn damage. For example, red berry varieties may show inhibition of color pigment synthesis to a progressive degradation of those already accumulated.

Thus, the need emerges to develop new low-water consumption protocols accompanied by the adoption of cooling systems. This project focused on the use of a delivery irrigation system limited to the portion of the canopy comprising the clusters. This approach offers a number of advantages, including (i) efficient conditioning with reduced irrigation use, (ii) the ability to schedule and automate delivery according to environmental conditions, (iii) exclusive cooling of basal clusters and leaves, leaving the rest of the canopy dry, and (iv) a water misting system, generally at on/off intervals, that provides rapid evaporative cooling and limits the time the canopy is wet.

Automation
Automation of the irrigation system was implemented with the SAPIR 2 control unit, equipped with three analog sensors to monitor the variables of air temperature, relative humidity, and dew point with recordings made at 10-second intervals. Management, programming and control of the system is done through the DREAM SPOT application platform, which is easily accessible from smartphones or tablets.

In-field testing
A multi-purpose system consisting of an irrigation line dedicated to each of the functions listed above was installed on three adjacent rows, oriented in a north-south direction, of Sauvignon blanc and Barbera, both of which were grown in counter-espalier, spurred cordon pruned, and with a 0.90 x 2.5 m planting spacing. Six healthy vines were randomly selected in each row for agronomic and physiological evaluation. An equivalent number of vines were selected from three adjacent rows used as a estate control.

• Anti-brine irrigation