page_title: Irrigation in viticulture
section_title: Impact of different soil types
hierarchical_section_title: Irrigation in viticulture / Factors influencing irrigation / Impact of different soil types
caption_attribution_description: (from author) "Lamella form in soils as clay is translocated downward through sandy soils."
context_page_description: Irrigation in viticulture is the process of applying extra water in the cultivation of grapevines. It is considered both controversial and essential to wine production. In the physiology of the grapevine, the amount of available water affects photosynthesis and hence growth, as well as the development of grape berries. While climate and humidity play important roles, a typical grape vine needs 25-35 inches of water a year, occurring during the spring and summer months of the growing season, to avoid stress. A vine that does not receive the necessary amount of water will have its growth altered in a number of ways; some effects of water stress are considered desirable by wine grape growers.
  In many Old World wine regions, natural rainfall is considered the only source for water that will still allow the vineyard to maintain its terroir characteristics. The practice of irrigation is viewed by some critics as unduly manipulative with the potential for detrimental wine quality due to high yields that can be artificially increased with irrigation.
context_section_description: Soil can have a significant impact on the potential quality of wine. While geologist and viticulturist are not exactly sure what type of immutable or terroir based qualities that soil can impart on wine, there is near universal agreement that a soil's water retention and drainage abilities play a primary role. Water retention refers to the soil's ability to hold water. The term "field capacity" is used to describe the maximum amount of water that deeply moistened soil will retain after normal drainage. Drainage is the ability of water to move freely throughout the soil. The ideal circumstance is soil that can retain sufficient amount of water for the grapevine but drains well enough to where the soil doesn't become water-logged. Soil that doesn't retain water well encourages the vine to easily sleep into water stress while soil that doesn't drain well runs of the risk of water-logged roots being attacked by microbial agents that consume all the soil nutrients and end up starving the vine.
  The depth, texture and composition of soils can influence its water retaining and draining ability. Soils containing large amounts of organic material tend to have the highest water retention abilities. These types of soils include deep loams, silty soils like what is typically found on the fertile valley floors such as in the California's Napa Valley. Clay particles have the potential to remain in colloidal suspension for long periods of time when it is dissolved in water. This gives clay-based soils the potential to retain significant amount of water such as the clay soils of the Right bank Bordeaux region of Pomerol. Many regions with these types of water retaining soils have little need for irrigation, or if they do it is usually supplemental during periods of drought. Soils with poor water retention include sand and alluvial gravel based soils such as those found in the Barolo and Barbaresco zones of Italy or in many areas of South Australia. Depending on the climate and amount of natural rainfall, areas with poor water retention may need irrigation.
  Just as having too little water is detrimental to the grapevine, so too is having too much. When vines become water-logged they become a target for various microbial agents such as bacteria and fungi that compete with the vine for nutrients in the soil. Additionally excessively moist soil is poor conductor of valuable heat radiating from the ground. In general wet soils are cold soils which can be especially problematic during the flowering causing poor berry set that could lead to coulure. It also becomes an issue during the ripening stage when vines in cool-climate regions may need additional heat radiated from the ground in order to sufficiently ripen its fruit (an example of this is the slate-based vineyards of the Mosel in Germany). Therefore, well draining soils are considered very conducive to producing quality wine. In general light-textured (such as sand and gravel) and stony soils tend to drain well. Soils heavy soils and those with high proportions of organic matter also have the potential to drain well if they having a crumbling texture and structure. This texture relates to the friability of the soil which can come from earthworms and other organisms that have burrowed tunnels throughout the soil. Much like rocks, these tunnels give water a freer passageway through soil and contributes to its drainage.
caption: Sandy soils typically have poor water retention but good drainage. However, if its mixed with significant amounts of clay, such as this soil sample, its water retaining properties will increase while still draining well.
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