The influence of relief and altitude on viticulture

The main areas of vineyards in all countries of the world, including the USSR, are located at an altitude of 400–600 m above sea level. However, in a number of countries and regions, grapes are cultivated at even greater altitudes. The criterion for determining the possibility of grape cultivation according to vertical zoning is the availability of heat and precipitation in the zones, the value of which depends on the geographical latitude of the area, altitude above sea level, and relief.

Due to the fact that in the southern, warmer zones and regions of our country the heat factor is not limiting, and in some southern regions of Central Asia it is even in excess, grapes can be cultivated here at higher altitudes than in more northern, less heat-provided regions. Thus, early grape cultivars on the southern slopes of the Crimean Mountains can be grown at an altitude of 720 m, on the northern slopes of the Greater Caucasus—1040 m, in Armenia and Azerbaijan—1400 m, on the southern and south-western spurs of the Gissar Range (Tajikistan) — 1960 m, and in the tropics — at an altitude of 2000 m.

With an increase in altitude above sea level, the sum of active temperatures decreases and the amount of atmospheric precipitation increases. In temperate latitudes, for every 100 m of ascent above sea level, the air temperature decreases by 1°C, and this primarily causes the ripening period of the berries to lengthen by 3–4 days and leads to a decrease in the sugar content of the berry juice. For every 100 m of altitude, the sugar content of berry juice in the conditions of Georgia decreases by 0.8–0.9%, and in Moldova and Azerbaijan — by 0.5–0.6%.

Along with this, in foothill and mountain zones, due to an increase in solar radiation (by approximately 18%), an effect of higher heating of plant organs and soil is observed, which leads to a decrease in the absolute value of temperature levels and their sums required for the onset of certain phases of the growing season, and the duration of the growing season as a whole. The difference in the magnitude of heating of the grapevine organs, primarily the leaf blade, on quiet, clear, sunny days can reach 8-10°C.

Along with vertical zoning, the exposure and steepness of the slope have an equally strong influence on the change in ecological factors. The terrain relief should be considered as a factor in the redistribution of heat in the surface layer of the air. By using southern slopes for vineyards, it is possible to significantly improve the thermal conditions of a zone with insufficient heat supply. The optimal slope steepness for temperate latitudes (46–50° north latitude) from the perspective of maximum heat gain is 25–35°. The further north one goes, the better the steeper slopes warm up. However, an agronomic correction should be made to this meteorological assessment of lands. On such steep slopes, tillage is difficult, therefore, slopes of no more than 20–25° should be used for grape cultivation.

Sloping lands have been used for grape cultivation since ancient times. Even the ancient Romans believed that grapes grown on hills had higher quality. Centuries of domestic and foreign viticulture experience have fully confirmed the correctness of this approach in choosing lands for grape cultivation. In our country, hills and mountain slopes are widely used for grape culture in Moldova, Ukraine, Georgia, Azerbaijan, Armenia, and the republics of Central Asia.

The influence of terrain altitude above sea level and slope exposure on the sum of active temperatures, air humidity, and sugar content of Rkatsiteli grape juice in the conditions of the southern part of Dagestan (according to Kerimkanova and Teimurova)

Difference in the sum of active temperatures, T, m V a l u e s b y i n d i c a t o r s o f a l t i t u d e a b o v e s e a l e v e l a b o v e s e a l e v e l, m 20 0 0– – 30 3 0 4 * 5 —

An altitude of 200–300 m above sea level is taken as the zero mark.

In the heat-supplied zones of the USSR, slopes exceeding 6–8° occupy more than 6.5 million hectares. In a number of farms in the North Caucasus, Transcaucasia, Crimea, the Carpathians, Moldova, and the southern regions of the European region, the area of vineyards on sloping lands can be increased by 120–160 thousand hectares.

In the northern, less heat-supplied viticulture regions, the best for grape culture are the southern, south-eastern, and south-western slopes, which warm up more, where grape plants are exposed to direct sunlight. In southern regions with a high sum of active temperatures, northern slopes are quite suitable, and in some cases even preferable (for the production of table and sparkling wines); vertical zoning, various exposures, and slope steepness leave a noticeable imprint on the thermal regime and illumination.

According to P. N. Unguryan (1956), the difference in air temperature between the warmest (southern) and coldest (northern) slopes in the central zone of Moldova in August is 4–5°C, and the difference in the timing of harvest maturation reaches 15 days. According to A. L. Popov and N. A. Popova (1983), in the central zone of Moldova, the sugar content of grape berries on plots with gray forest soil on a south-western slope was 2–4.2% higher than on a north-eastern one. On slopes, vineyards are better illuminated and ventilated, and less susceptible to the impact of frosts. Due to better aeration, plants are less affected by fungal diseases — downy mildew, powdery mildew, and gray mold.

In the conditions of the foothill-mountain zone of southwestern Uzbekistan, due to a more favorable temperature regime during the winter period, grapes on slopes can be cultivated without cover for the bushes for the winter, while in the flat part, the bushes are covered with soil. Lowlands are the least suitable for grape culture, as cold air accumulates there during winter, early spring, and autumn, creating an unfavorable temperature regime for the overwintering of plants.

The influence of water bodies and wind on the vineyard microclimate

Proximity to large water bodies — seas, lakes, and rivers — softens the continentality of the climate and improves conditions for vine growth. The water surface optimizes air temperature and humidity due to the constant movement of air masses throughout the day. This is precisely why the world’s leading viticultural regions — from European river valleys to the Black Sea coast and the Great Lakes in the USA — have historically been located near water. When designing new plantings, such plots should be occupied first.

Wind affects the vine both mechanically and through changes in humidity and temperature. During the period of full canopy development of the bushes, the microclimate inside the vineyard begins to change at a wind speed of 1 m/s (if it blows along the rows) or more than 2 m/s (if the flow is directed across). A wind force of 4–5 points injures green shoots and bushes, and stronger gusts are capable of destroying the trellis. The risk of such damage is particularly high in windy zones, for example, in the areas of Anapa, Gelendzhik, Taman, and the Absheron Peninsula.

• Microclimate change along the rows — from 1 m/s
• Microclimate change across the rows — more than 2 m/s
• Shoot damage by wind — 4–5 points
• Duration of cold northeasterly wind — 2–3 weeks

Hot dry winds blow from the deserts in Central Asia, Dagestan, and neighboring regions. They cause a sharp drop in relative humidity of the air and an extreme rise in temperature. Dry air scorches the berries, depriving their skin of elasticity, which causes them to stop growing. As a result, coloring and aromatic substances form more poorly in the grapes, which reduces the harvest quality.

Not every movement of air is harmful to plantings. A moderate warm wind during the flowering period carries pollen and improves pollination. During prolonged rains, the wind aerates the soil and the canopy of the bushes, reducing the risk of fungal disease development. However, in case of a soil moisture deficit, a dry wind only exacerbates the situation by accelerating water evaporation.

Methods of protecting plantings from wind and hail

The harmful effect of wind on grape plants can be reduced with the help of preventive measures even at the planting stage. For this, the vine is placed on slopes or in wind-protected microzones. Agronomists also establish windbreak strips and carefully select the orientation of the rows.

• placement of plantings in protected microzones;
• utilization of terrain slopes;
• creation of windbreak forest strips;
• calculation of optimal row orientation.

Hail causes heavy damage to the vine during the growing season. Hailfall is usually local in nature and limited to a small area of a few kilometers. Vineyards in Georgia (in particular, in Kakheti), Azerbaijan, Moldova, and some regions of Russia suffer from this most frequently.

The degree of damage to vineyards by hail depends, on one hand, on the size of the hailstones, the intensity and duration of their fall, and on the other, on the phenological phase of the grape plant. Hail is most harmful when it falls during the later phases of the growing season — during the period of full canopy development of the bushes, and in the phases of flowering, growth, and ripening of the berries. In this case, the hailstorm causes damage to the harvest not only of the current year but also significantly affects the next year's harvest, since young shoots and overwintering buds are damaged, and in the case of severe hailstorms, so are lignified shoots. Wounds inflicted on the shoots cause a disruption in the normal functioning of the vascular-conducting system and impair the metabolism of the grape plant.

Recommended and practically applied techniques for protecting vineyards from hail include the use of special rockets to prevent the formation of hail-bearing clouds and subsequent hailfall, as well as the installation of protective devices over vineyards in the form of fine-mesh synthetic nets. The latter technique has become quite widespread in Kakheti.

The formation and modification of ecological factors are influenced not only by the geographical latitude of the area and the terrain. The peculiarities of the climate that arise under the influence of relief, exposure and steepness of slopes, soil types, types of plant communities, waterlogged and drained areas, irrigation, and methods of soil management in the vineyard are called the microclimate. Individual ecological factors, such as air temperature and humidity, the radiation regime, and others, are in turn influenced by the vineyard plantings.

The microclimate that forms under the influence of plants within the area of the vineyard plantings (agrobiocenosis) and in the zone of an individual vine is called the phytoclimate. As is known, the object of ecological research is the soil-plant-atmosphere system. From the point of view of agricultural practice, the central link of this system is the agrobiocenosis — a community of plants interacting continuously with the environment.

When examining the phytoclimate, it is necessary to distinguish between the influence of an individual plant and that of a plant community — the agrobiocenosis.

The phytoclimate of vineyard plantings—a biocenosis, and in combination with technological practices, an agrobiocenosis—differs significantly from similar climatic indicators of a meteorological site located in an open area.

According to T. G. Kataryan and N. S. Potapov (1963), in a vineyard during the summer period, there is a clearly defined pattern of air temperature decrease from the soil surface to the top of the vines during the day, and a less pronounced change from bottom to top at night.

The regime of air and soil temperature and humidity changes significantly with different planting schemes. With an increase in planting density, air turbulence decreases due to reduced ventilation, as a result of which the air humidity in the vine zone is higher than in the inter-row spaces.

An important element in justifying the feasibility of switching to a more progressive cultivation technology for grapes in the zone of non-covering culture with a high trunk and wide inter-row spacing is the indicator of better illumination of the vines and more favorable phytoclimate conditions in the new type of vineyard plantings.

In grape culture with a high trunk, the pattern of higher temperatures in the winter period at a height of 1–1.5–2 m is better utilized compared to the surface layer. Good ventilation of high-trunk plantings in rainy years allows for reducing the risk of harvest damage by gray mold. The phytoclimate changes significantly under the influence of various vine training systems, consisting of:

• a vertical plane;
• a horizontal plane.