Need of the vine for irrigation

After heavy rains, severe drought usually occurs in our latitudes. Therefore, we decided to share with you this material related to the need of the vine for irrigation. We hope that the information in it will be useful to you!

Irrigation of the vine.

The need for irrigation in the cultivation of the vine crop in Bulgaria is determined by the quantitative and temporal discrepancy between the needs of the plants for water and its presence in the soil.

Water scarcity inhibits the growth of the vines, and the ripening of the grapes can be slowed down or stunted. Vegetative growth is more affected than yield. On the other hand, the abundance of water stimulates unnecessary vegetative growth, which leads to thickening of the foliage, high water content of the berries, compacted bunches due to the increased size of the berries, poor illumination of the bunches due to their shading and the development of diseases.

When considering the problem of ensuring an optimal water regime for vines, it should be borne in mind that, unlike many fruit crops, the vegetative growth of the vines precedes flowering and fruit growth, and the degree of overlap between these phenophases varies from one variety to another. 

The irrigation regime of vines depends on the strength of the vines’ growth and their development phases during the growing season, i.e. phenophases. Plants begin to consume water with the bursting of buds, and their needs are constantly growing with the development of leaves and shoots. By mid-June, the vines were fully developed and water consumption peaked in the second half of June, July and August. According to the changing water needs of the vines during the growing season, the irrigation regime is usually organised in four main stages.

The first stage covers the time after the buds burst to the end of flowering. Due to the insufficient development of the vines during this period, the water consumption of the plantation is low. Water supply and rainfall are often sufficient to meet the needs of plants. However, water scarcity can lead to non-simultaneous cracking of the buds, weak growth of shoots and fewer flowers. Water deficiency during flowering is associated with poor pollen and pistil vitality and, therefore, weaker grain deposition, which can reduce yield to 50 %; The size of the nested grains is also negatively affected. The suppressed growth due to possible drought during this stage may be reflected in insufficient foliar area, respectively insufficient capacity for synthesis of photoasimilates, necessary for the growth and nutrition of the fruits in the subsequent phenophases. The yield in the following year can also be negatively affected, as the laying of the inflorescences in nodes 1-4 begins approximately two weeks before full flowering and lasts about two weeks. It is believed that water scarcity at this time decreases the number of inflorescences on one shoot rather than the number of flowers in one inflorescence that develop later.

The second stage begins after flowering and continues until the beginning of the ripening of the fruits. The beginning of the stage coincides with the first phase of the development of the nipples. This is the period of cell division in the grains and their subsequent initial growth, during which the satisfaction of water needs is of utmost importance for the quantity and quality of yield. During this phase, the nipples are highly sensitive to water stress, as a result of which they remain small in case of possible water shortages. This thinning of the grains cannot be compensated by optimising the water regime in subsequent phenophases, and yield losses reach 40 %. The end of the stage coincides with the second phase of the development of the grains, during which their growth is noticeably slowed down and their size is not significantly affected by water scarcity. However, sprout growth continues and possible water stress would have a limiting effect in this regard.

The third stage continues from the beginning of the ripening of the fruits to the harvest. As a rule, vines are not so sensitive to water stress during this period. Growth is almost subdued and can hardly be influenced by the lower water status of plants. However, drought at the beginning of the period can cause the lower leaves to fall off and the bunches to be bare with subsequent sunburns on the grains. Any water shortage at this time does not have a significant impact on the size of the grains and, consequently, on the quantity and quality of the yield, although this stage coincides with the third phase of the development of the grains, when they resume their rapid growth, reach maximum size and ripen. However, high levels of water stress cause drying on the tops of the shoots, as a subsequent higher irrigation norm or higher precipitation can stimulate the growth of lateral shoots. The growth of lateral shoots at this time deflects photoasimilates, hinders the development of fruits and slows their ripening.

The fourth stage begins after the harvest and ends with the dropping of the leaves. During this period, the water consumption of the vineyard gradually decreased. The irrigation regime should support the physiological processes in the plants without causing secondary growth. Mild to moderate water stress inhibits the strong growth of some varieties and promotes the ripening of shoots. A stronger water scarcity can suppress root growth with subsequent reduced mineral nutrient extraction from the soil and potential micronutrient scarcity next spring. This can be reflected in premature or delayed cracking of the buds, slowing of growth and even collapse of young shoots. In late October and early November, when low temperatures hamper secondary growth, irrigation rates may be raised in order to restore the water supply to the active soil volume.