Benefits of mechanical pruning of vines

Wine growing is an important activity for the sustainability of small properties in Brazil and consumes a significant amount of labor to carry out field operations, a workforce that has become increasingly scarce over recent years. At the same time that cultivation is expanding, new wine production hubs, both national and international, have put pressure on the sector's industry, which seeks to adjust to the competition of new times.

The vine presents a free form in a natural environment, where the mechanism of self-regulation of growth and development prevails. Generally, unpruned plants have an alternation of harvests, that is, years with high production, followed by years of low production. Pruning as a management strategy aims to balance the number of fruits and vegetative development, control the canopy architecture and adapt growth and development to the economic exploitation of the crop.

Vegetative management is a common practice applied to vines and aims to improve the distribution of branches and leaves to favor the capture of solar radiation, reduce shading inside the canopy and avoid the formation of a microclimate favorable to the development of diseases. The balance between leaf area and production benefits plant development and grape composition.

In general, vegetative management can be classified into formation, production and cleaning pruning, and may receive different denominations according to the times in which they are carried out (winter and summer pruning), with the leafing of plants (dry and green pruning) and its intensity (drastic pruning, renovation, skeletonization, etc.). Vegetative management is linked to a sequence of operations (disbudding, topping, thinning of flowers and fruits, among others) during the development of the plant.

It is important to highlight that production pruning can be divided into pre-pruning and pruning itself, when the branches are initially cleaned and then pruned.

Given that grapevine cultural treatments require a significant amount of labor to carry out field operations, mechanization of vineyard management operations has been used throughout the world with the aim of facilitating work. field and overcome labor shortages, in addition to reducing production costs. An adoption of around 50% of mechanization in vine management operations has been observed for some decades now, in wine production regions in several countries. Australia is one of the countries with the highest rate of application of mechanization in all wine management operations. In Brazil, the adoption of management mechanization in the wine chain is still incipient, with some initiatives in isolated points in the South and Northeast.

 When considering the adoption of mechanized pruning, topographic and soil conditions and the standardization of cultivation systems that allow its implementation must be taken into account. Some wine growing systems are more conducive to mechanization than others. The espalier vine cultivation system is more conducive to the implementation of mechanized pruning, but all vine training systems can be adapted to mechanized management practices, especially grapes grown for wine and juice.

The adoption of partial or total mechanization of the management of any crop suggests an approach to the consequences of such practices on the quality of production, in comparison with manual management.

Considering only mechanized pruning of the vine, the adoption of this practice influences the ecophysiology of the canopy, the composition of the yield and the quality of grape derivatives, with results in this area being more abundant for varieties of Vitis vinifera. However, studies carried out at the Agronomic Institute (IAC) have focused on the impact of this practice on hybrid cultivars.

At first glance, the adoption of mechanized pruning has a direct impact on production costs and the speed of operations. Work carried out in the area of ​​vine management mechanization demonstrates that production costs are significantly reduced. There are reports of a 50% reduction in production costs in vineyards, when mechanized pruning was used followed by manual pruning to remove remaining branches.

Generally, at the beginning, the adoption of mechanized pruning may cause a small reduction in production and grape quality in already established vineyards. However, after two to three years, production and quality return to levels equivalent to manual handling. However, the reduction in cultivation costs compensates for the eventual reduction in grape productivity. Pruning automation has worked best when applied to young vineyards, already established for this purpose, although it has also worked in already established vineyards; in this case, requiring more time for adaptation.

At the Agronomic Institute (IAC), an assessment was carried out on the impacts of adopting mechanized vine pruning. A prototype pruner, developed at the Institute itself, has been successfully used to operationalize vine pruning.

 The evaluations were carried out in a “Isabel precocious” vineyard, in rows cultivated in espalier, with a spacing of 3m between rows and 2m between plants, with rows 120m long. The establishment of 3m between the rows was used to avoid soil compaction near the plant's root zone; The spacing between plants, 2m, is linked to facilitating the mechanization of weed cleaning in the planting line; the height of the posts was established at 2,20m above the ground, which allows the pruning machine to pass easily.

The pruning practices carried out over the years constitute the initial pre-cleaning (pre-pruning), which consists of a straight cut along the plants' conduction cord, leaving around six buds per pruned branch. After passing the machine, a manual transfer is made to lower the gems. Emphasizing that the cutting height of branches is linked to the operator's operational skill.

The times set for passing the machine, in pre-pruning, are, on average, five minutes for a distance of 120 meters, for this operation.

Depending on the variety and microclimate, manual transfer could be dispensed with, depending on the load index planned for the vineyard, which consists of the relationship between the vegetative and reproductive parts, which must be studied for each variety in its growing environment. .

An important characteristic that occurs in vineyards subjected to mechanized pruning is that a small number of branches will not sprout in the year of pruning, due to small fluctuations in the cutting height. As a result, over the years, these dead branches will accumulate, requiring eventual cleaning to eliminate them.

In studies carried out at the IAC, data were collected to evaluate the composition of the yield and the physical-chemical composition of the berry, and the complexity of the wine obtained.

In general, the results show that the adoption of mechanization of the vineyard pruning process (established for mechanized pruning) did not influence the quality of the early Isabel grape, when compared to manual pruning management, over the years. There was no influence on the number and weight of bunches, nor were there any significant changes in the content of soluble solids, anthocyanins, total phenols and tannins. In the case of the Isabel cultivar, no influence on the quality of the wine was observed.

It should be noted, however, that due to the range of vine varieties in use in the country, in varied microenvironments, more studies are necessary to verify the direct impacts on varietal behavior and production quality, which must be carried out, specifically, for each cultivar, for a certain number of harvests, before being widely recommended.

Observing results from similar studies, it was found that some authors report differences in productivity, more favorable to vines grown under mechanized pruning, with minimal differences in the quality of the wine produced.

On the other hand, there are cases in which a significant decrease in vine vigor was observed when vineyards were subjected to mechanized pruning.

There are reports of observations comparing manual pruning and mechanical pruning, during some years, where an increase in productivity was observed when mechanized management was adopted, but with the need for a renewal in the formation of the plant after five years of mechanical pruning, to promote the renewal of the gems.

In general, for a wide range of varieties, long-term observations show that when mechanized pruning is adopted, the number of bunches increases, but weight decreases, with a natural compensation occurring, tending towards equality in productivity, between the manual and mechanized pruning management.

This reinforces the fact that there is no general rule regarding the response to mechanical pruning. Each variety has to be studied separately, as the result depends on several factors, arising from the interaction of the soil-plant-atmosphere system, in addition to the plant-machine relationship.

Maria Aparecida Lima, Antônio Odair Santos, Engineering Center/CEA, Agronomic Institute (IAC)

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