Planting Density: Not too Far yet not too Close

Of all the factors that influence quality, the terroir is the most important one, followed by vineyard layout, particularly planting density.  But what appears to be more relevant is the need to achieve perfect balance between inter-row and in-row spacing.  And this is no easy task.

Climate and soil characteristics are the main factors to consider when establishing a new vineyard, but by no means should they be the only ones. Other variables to bear in mind are water availability, the terrain’s topography and altitude, and the distance to the different facility centers (vendors). A wrong decision may bring about catastrophic consequences, especially if we consider that, according to a study conducted by Francisco Gillmore, the approximate value of establishing a new vineyard exceeds USD 20,000 per hectare, to which we must add the value of the property.      

Once it has been determined that the conditions are favorable for planting vines, comes a second set of decisions that has to do with the training system to be utilized as well as planting density, which will depend upon production goals and the potential vigor of the soil. 

There are over 60 training systems, but most of them are only utilized in their area of origin. Other systems are more commonly used, like vertical shoot positioning, lyre, tendone and Scott Henry, which are precisely the most widely used in Chile.

Shoot positioning was introduced in our country by technicians from the Bordeaux area, who arrived in the wake of the phylloxera crisis that ravaged European vineyards. Vertical shoot positioning –the most commonly used given its ease of management and the fact that it uses mobile wires to guide the shoots vertically-, allows high planting density and is very suitable for medium to low vigor soils. The Scott Henry (two fruiting wires, where half of the shoots are trained in an upward direction while the other half is trained downward), the lyre system (two walls of shoots trained in an upward direction) and the Geneva double curtain (two inverted walls of shoots trained in a downward direction) are suitable for high vigor soil, for they split the canopy.  

Each system has its pros and cons, so choosing one in particular will depend mainly on production goals, both in terms of quality and quantity, and the potential vigor of the area selected for establishing the vineyard.

SEEKING THE AVERAGE

Vigor is the key concept here. “The goal is to achieve medium vigor in the vineyard, regardless of the terroir selected,” says Pedro Izquierdo, viticultor at Viña Errázuriz. Excessive vigor will result in large and diluted berries, whereas weak vigor will produce leaf populations that are unable to secure tissue maturation.

That is why the first step should always consist of knowing the vigor of each square centimeter in the vineyard. In the Soquimich Saltpeter Agenda, Yerko Moreno -agricultural engineer at the Vine and Wine Institute of Universidad de Talca- states the necessity to conduct detailed soil studies by means of soil pits, whose location and number will depend upon the uniformity of the land to be studied. “In uniform terrain, one soil pit may suffice for 2 to 3 hectares, but highly uneven terrain may require between 1 and 2 soil pits per hectare. Careful observation of the existing vegetation and the farming history of each individual sector will provide information concerning the degree of variability of the soil and will serve as a guide when conducting further soil studies.”

The information from each soil pit will serve the purpose of mapping the soil, showing homogeneous units in terms of effective depth, moisture retention and growth potential of the vineyard.  Only after this information has been made available will it be possible to determine the best planting density. It should not be forgotten that the ultimate goal of planting design must always be to capture as much light as possible and convert it into the largest possible amount of chemical energy per surface unit of the soil. We must also highlight the fact that vineyard yield depends mainly on the distance between rows, while fruit quality depends mainly on the plantation density along the same row.

OPPOSING TENDENCIES

When the time comes to determine plantation density, there are two schools with totally opposing tendencies. The so-called New World school is led by Australian-born Richard Smart, who has drawn attention on the question of light and vineyard quality. He states that density should allow for the complete expression of the terroir and, therefore, planting density should decrease in a high-vigor soil in order for all growth points to achieve full expression. That is the only way to obtain medium vigor.

On the other hand, the Old World traditional school, under the leadership of French enologists, states that in order to obtain medium vigor in a highly vigorous soil, plantation density must be increased. In other words, vines should be planted closely enough to allow their roots to compete with each other, which ultimately results in decreased vigor.

Pedro Izquierdo considers both approaches valid. “It is not that one is correct and the other is not. As a matter of fact, in our vineyard we use both approaches, but my experience tells me that high density makes it easier to achieve the desired goals. For example, medium vigor is more easily obtained on vigorous soil with high density (7,000 plants/ha) than with 3,500 plants/ha. It will also depend on the grape variety chosen, for some are naturally more vigorous than others.”

Another important factor to consider is soil depth. “A study conducted in South Africa confirmed that roots grow a lot in deep soil, without the need to limit aerial growth. That is why it is easier to obtain medium vigor when limits are imposed on root development,” says Izquierdo.

A MATTER OF DISTANCE

The two variables that will ultimately determine planting density are distance within the same row and distance between rows. That is why the mere knowledge of density is not very helpful, since it does not allow obtaining similar results with totally different vineyard layouts.

Let us see one example: in a plantation with an interrow distance of 2.3 meters and an in-row distance of 1.2 meters, the resulting density will be 3.623 plants/ha. The same density will be obtained in a vineyard with interrow distance of 3 meters and distance between plants in the same row of 0.92 meter. The difference lies in the fact that the first will occupy 4,347 lineal meters, whereas the second will only occupy 3,333 meters.

Distance between rows is defined in terms of the slope gradient and the size of the machinery to be utilized. Thus, plantation on contour lines, on steeper slopes, will necessitate wider interrow spacing, says Yerko Moreno. Similarly, if the rows are oriented in the same direction as the slope, the distance between them may be much greater when compared with a plantation in contour lines. Still, precautionary measures against erosion may become necessary. The general principle should be to achieve the shortest possible distance, although canopy height must always equal or exceed distance between rows.

In-row planting density, on the other hand, is a bit more difficult to define and will depend on the cultivar chosen, rootstock vigor, the soil’s potential vigor and the training system to be utilized, states Yerko Moreno in his article. “In general terms, a deeper soil and greater vigor of the cultivar selected will require wider in-row spacing or, alternatively, a training system that considers canopy splitting techniques. In this sense, drip irrigation is a vital tool in our efforts to keep plant vigor under control, and consequently will greatly influence the manner in which a plantation’s density will be determined.”

In conclusion, what we look for is a density that not only deters bunch overproduction, but also that eliminates leaf shading, so that the microclimate obtained ensures the best possible fruit quality.

And this is not a question of dogmas. “Here, experience is greatly appreciated, we value what our neighbors are doing; intuition is highly trusted,” says Izquierdo. And experimenting is also very important, of course. This is precisely what he is doing with a hectare planted to Syrah on a slope in the Panquehue vineyard, with southern exposure and no problems regarding luminosity. There, two things call our attention: the training system and the density. Izquierdo placed his bet on the Gobelet system, in which each individual plant leans against a wood post, in the manner of a tree tutor.  He planted at high density –10,000 plants/ha- in a 1:1 ratio (1 meter between rows and 1 meter between plants within the same row). “I believe this is the most dense Syrah plantation in Chile,” he says. What will the grape quality be like? We need to be patient and wait until the vineyard achieves its full expression.

What is clear is that every vine grower pursues the perfect combination for each particular case, for he knows that this is a key decision that will affect the quality of the wine obtained. Pedro Izquierdo confirms it: “of all the factors that influence quality, the terroir is the most important one, followed by vineyard layout, particularly planting density.” As simple… and as complex as that.

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EFFECTS OF THE DIFFERENT PLANTING DENSITIES

During the 1994-1995 season at the Cauquenes Experimental Center of  Instituto de Investigaciones Agropecuarias (Institute for Agricultural and Livestock Research – INIA), the effects of six planting densities (1,250; 2,500; 5,000; 10,000; 20,000 and 40,000 plants/ha) were evaluated on Chardonnay and Cabernet Sauvignon cultivars subject to drip irrigation, trained on  double inverted cross pieces and formed as a unilateral cordon.

Results were as follows:

Vegetative growth: the trunk area and pruning weight per plant decrease as plantation density increases. But this tendency reverts when growth is measured in terms of area (hectares). This proves that a vine population that more densely occupies the space available achieves greater total growth indexes.

Productive behavior: Each plant’s individual growth also decreases as density augments. Chardonnay showed greater per-plant productivity in densities over 5,000, 10,000 and 40,000 plants per hectare. In the case of Cabernet Sauvignon, the highest individual yield was achieved with densities of 2,500 and 5,000 plants/ha.

Canopy luminosity and temperature: they decrease as density increases. In vineyards with 40,000 plants/ha, luminosity levels drop drastically as a result of canopy shading, which in the case of Cabernet Sauvignon entails a decrease in bud fertility and, consequently, in production as well. Such behavior was not observed in the case of Chardonnay, which may lead to the conclusion that this red variety is more sensitive to lower levels of luminosity than its white counterpart.

Hydric potential: plants in higher densities present potentials that are less restrictive when compared with lower densities.

Chemical composition of the musts: at higher densities, higher levels of malic acid were detected in musts from both varieties. In the case of tartaric acid, greater levels were measured in Chardonnay musts from lower density areas, and in Cabernet Sauvignon musts from zones of medium density.

Alcohol content: in Chardonnays, planting density did not affect alcohol content, whereas in Cabernet Sauvignons, the alcohol content was lower in those wines from high density areas. All wines achieved the minimum legal alcohol content.

Quality: the effects of planting density on the qualitative attributes of the different wines were not as marked for the panel to notice significant differences. As for overall quality, only Chardonnay from 5,000 plants/ha was rated better than that from 40,000 plants/ha. Except for its color, Cabernet Sauvignon from 2,500 plants/ha areas was consistently rated lower than that from 20,000 plants/ha areas.

In conclusion, recommended densities for Chardonnay fall within the 5,000 to 10,000-plants/ha range, while those for Cabernet Sauvignon fall between 2,500 and 5,000 plants/ha. These recommendations must also consider edaphoclimatic conditions in the Cauquenes area, formation systems and vineyard training systems, as well as aspects related to management and plantation costs.