K.H. Fisher, University of Guelph, Vineland Station, Ontario
The effects of poor soil drainage on grapevines
Commercial vineyards, whether grafted or own-rooted vines, should be planted on soils with good natural drainage. ‘’Vinifera’’ grapes (i.e., most commercial wine and table grapes) will not tolerate poorly drained soil conditions, especially when own-rooted. Native American grapes and most interspecific hybrids are more tolerant of wetter soils, but all vineyards can be improved with the installation of subsurface tile drainage to improve wet conditions.
Root health is critical for the long term success of a vineyard and much can be done to affect this root health with the choice of appropriate rootstocks. If the soil contains phylloxera or nematodes, appropriate rootstocks can confer some degree of resistance. If the soil contains high amounts of some salts, other rootstocks can also mitigate the effects of those conditions. However, specific rootstocks are only marginally different in their ability to withstand very wet soil conditions, and the most obvious way to fix the problem is to improve the natural surface drainage of the site with judicious land contouring and the installation of subsurface tile drainage prior to planting.
A vine is healthiest and most active when the root system is large and actively growing. A highly ramified root system means a great number of active root tips for exploration and water/mineral uptake. A large structural root system means a good supply of carbohydrates and amino acids for overwintering and spring remobilization. Roots are also the site of cytokinin and gibberellin production, both critical to many metabolic functions within the whole vine.
Grapevines, being perennial, will explore large volumes of soil given the right soil moisture, pH and texture conditions. The pattern of exploration and the soil conditions tolerated differ slightly among species, but the basic restrictions are common to all plants – physical impediments, sudden changes in soil chemistry, and anoxia (lack of oxygen), usually because of high water tables. Of the three, soil water content is probably the most critical as it directly affects root health and function. (Note: In low pH soils, pH may be as limiting as anoxia in waterlogged soils due to limiting phosphorus availability and aluminum toxicity.)
Vines are relatively tolerant of standing water during dormancy, when temperatures are low and respiration rates are minimal, but anaerobic breakdown will eventually initiate rotting of flooded tissues. When a vine is in full leaf, this process is greatly accelerated. The low oxygen regime in the root zone will drastically impede water uptake, an active metabolic function requiring oxygen. In the meantime, the leaves are transpiring rapidly. With sunlight and high temperatures, there is a high replacement water demand from the root system, the vines will rapidly wilt, and tissue death can follow quite quickly. Perhaps complete flooding of the vineyard is a rarity, but high water tables, poor drainage and frequently wet soils create a constant stress on the whole system and vines will not flourish. In areas close to the northern (or higher elevation) limits of commercial vineyard production, this stress often results in excessive winter injury. Saturated, frozen soils can also cause physical injury around the soil line leading to formation of galls in vines infected with the crown gall bacterium Agrobacterium tumefaciens.
Soils that are naturally at risk for these conditions would be high in silt and clay (40 to 50 percent and 30 to 40 percent, respectively). These could be soils found in areas of frequent rainfall, making drainage an issue all year, or they could be in areas where winter rain/snow constitute a major portion of the annual precipitation. If the latter is the case and the vineyards are in the warm, dry Mediterranean parts of the continent, this winter rain is the reservoir for the summer dry season. But if the vineyards are northerly (or at high elevation), the spring conditions are cold, the soils need to warm up quickly to induce rapid spring growth required for a short season area, and dropping the high spring water table rapidly through the use of drainage tile could vastly improve the productivity of the vineyard. Vineyard sites or portions of sites that are in river bottoms or where water pools form should be avoided for this and many other reasons.
Soils that have persistent high water tables can be identified by the mottled coloring in the soil profile as a result of reduced iron deposits. This is called ‘gleying’ and is usually yellowish-brown or blackish-brown. If these formations show up within 20 to 30 cm of the soil surface, this means the root zone of the vine will be subject to the same wet, anaerobic conditions. In northeastern North America, the winter/spring water table can easily reach the surface in imperfectly drained clay/clay-loam soils, but if tiled, it does not usually reach higher than 40 cm below the soil surface, leaving winter roots in good, well aerated conditions.
Other impediments to good root growth are physical and chemical barriers. Soils with a bulk density greater than 1.5 gm.cm-3 will generally restrict fine root exploration, whereas soils with a lower strength of 1.1-1.2 gm.cm-3 are considered ideal. Many of the clay loams in the northeast are as dense as 1.8 gm.cm-3 and all management techniques that strive to reduce this density are to be encouraged, tile drainage being one of them.
Tiling, or tile drainage, is a practice that removes excess subsurface water. In a tile drainage system, a network of perforated plastic pipes, called drain tile, is installed under the vineyard. When the water table rises to the level of the tiles, the excess water flows into the drain tile and along the network to a drainage ditch, moving the water away from the vineyard.
In order to maximize yields, farmers often try to control tightly the water regime in their fields. This is done in two main ways: irrigation, and subsoil drainage. Subsoil drainage is accomplished by laying perforated plastic pipe, called drain tile, at a prescribed depth in the soil. If the water table rises to this level, the excess water flows into the drain tile and flows along (within) the tile, to a drainage ditch (below), from which it exits the field.
Although good drainage theory would recommend the installation of tiles perpendicular to the slope, to encourage gravity feed of the tile both vertically and horizontally, most vineyards are tiled parallel to the rows regardless of the slope. This is purely convenience, so tiles can be easily located when installing posts to prevent puncturing and disrupting the flow of drainage water.
A vineyard should be tiled before planting, but any land contouring should be completed and allowed to settle before installing the drainage tile. A qualified drainage engineer should develop the tiling plan to ensure the appropriate depth, slope, and outfalls for the vineyard. Any discharge of drainage water off the drained property must comply with local or state water authority guidelines.
Most drainage tiles are perforated, ribbed, continuous plastic tubing, usually 100 mm in diameter, but occasionally 50 mm or 75 mm for specialized tasks. In areas where soils are quite coarse, a nylon sleeve is usually employed to prevent the drains from silting in. This isn’t necessary in clay or clay loam soils because the tiling plow creates a stable trough for the tubing. Mains are usually 150 mm in diameter, are often rigid to withstand traffic, and not perforated.
In some instances, mole drains are employed. These are similar to tiles but without the tile itself installed. Soils must be at least 30 percent clay and 40 percent silt for the trench to remain stable for a couple of years, and the inlet created by the shank of the plow to remain open. These are cheaper, but only suitable where soil depth and slope can follow the land profile and there is little traffic down the center of the row. Any frequency of wheel traffic will collapse the mole, especially at the outlet.
In the northeast, tiles are generally installed at 60 to 80 cm deep in clay loam soils. If installed deeper, the water takes too long to reach the tiles and the drainage is quite slow and less effectual. Shallower installation can sometimes be disturbed by field work, such as subsoiling or deep plowing. Tiles are not usually backfilled when installed using a tiling plow. However, if installed using a trenching machine, the backfill is usually the native soil brought up during the trenching process. In some cases where drainage is particularly problematic and the tile must be installed deeper than is recommended, the tiles will be backfilled with small gravel to aid water percolation. The ridge created during installation will be quite noticeable if the soil is very dry, but will settle over time. It should not be flattened with a dozer blade because of potential compaction and interference with natural percolation to the tile depth.
Although most tile systems are systematic throughout a vineyard, there are some instances where interception tiles can also be very useful. Fields that back up to a hillside where seepage is a problem can use a tile parallel to the hillside to intercept seep water before it enters the vineyards. These can be deflected around the vineyard and meet the mains farther down slope. Open drainage ditches can accomplish the same thing but can often overflow, particularly in the spring melt season when the surface is still frozen. A tile will continue flowing as the soil underneath is often not frozen.
All tiling systems should have a proper exit grate to prevent animals from using the tiles as a temporary home. All exits should flow properly into a ditch below grade to accelerate movement of water away from the field, but again should comply with all local and state water authority regulations.
Costs and Benefits
Costs of tile drain installation will not be given here, as each area will have its own contractors with their own costs. However, a trial done in the Niagara Peninsula area of Ontario, Canada showed that even with a low value variety like Concord, which has considerable tolerance for wetter soils, only 1.2 tons/acre improvement over the existing production would pay for the tiles (100 mm, every row) if costs were amortized over ten years. Needless to say, more valuable grapes (Chardonnay, Cabernet franc) required only 0.22 tons/acre improvement to pay for the tiles.
Perhaps more important is the overall improvement of vine health when a vineyard is properly contoured and tiled before planting. In areas where winter injury is a constant threat, improved vine health, particularly root health, will play out as improved overwintering capacity. With improved overwintering capacity, you have improved consistency in the vineyard. And with improved consistency, your total costs decrease because more work can be done mechanically. Pruning, thinning, leafing, crop control, and even harvesting decisions do not have to be made individually, vine by vine.
Installing Drain Tile in Vineyards video, Cornell University
Drainage of Wet Soils, Michigan State University
Irrigation Basics for Eastern Washington Vineyards, Washington State University
Reviewed by Tim Martinson, Cornell University and Sara Spayd, North Carolina State University