I am not an expert in soil drainage and we do not currently have any experiments addressing it but I get asked about it often. So here is one for the growers that tell me that they are on 'real grape ground.'
What I do know and have researched is that most of the growth potential in the vines this spring is in the root systems. The majority of the stored carbon, nitrogen, and phosphorus needed for early leaf area development and new root growth start to remobilize near bud swell. The process of remobilization is based on cellular respiration in the roots and cellular respiration is largely dependent on temperature and oxygen. Therefore, soil temperature and oxygen are very important in spring grapevine growth.
Lets first deal with temperature. We talk about warm gravel soils and cool clay soils in the grape belt. Gravel and clay soil particles warm up and cool down the same; however, it is the water in the soil that changes the temperature of the soil. If there is a lot of water in the soil, more solar energy goes into evaporating water and less goes into warming up the soil. If a soil is well drained, more solar energy goes into warming up the soil. Therefore, the well-drained gravel soils in the belt warm up faster than the less drained clays. That may be, at least in part, why route 20 gravel vineyards start a few days earlier than route 5 clay vineyards. Although, other factors come into play like proximity to Lake Erie and nighttime temperatures (well drained gravel soils also cool down faster at night).
Can you do anything about soil temperature and would it make a difference in spring growth? As stated, well-drained soils warm up faster than wet soils. Bare soils warm up faster than soil with green cover or mulch. Dark colored soils warm up faster than light colored soils. Does a well-drained vineyard with a bare floor of dark soil warm up and start growth earlier than other vineyards? It should; however, it is difficult to prove it because of the other factors mentioned before. Is early soil warm up desirable? Keeping the soil cool may inhibit bud swell, which might be good for frost protection. However, once growth starts, increasing soil temperature as fast as possible will help increase root respiration and resource remobilization. Personally, I would rather hold the vines back a few days in the spring and deal with ripening efficiency later in the season. There are approximately 100 days from bloom to harvest. I would much rather put my efforts into crop load, water, and pest management during those 100 days to improve fruit ripening than worry about moving up bud break by a few days in the spring.
Soil oxygen can be a bigger issue. You and I need oxygen for cellular respiration in our bodies. Roots cells need oxygen for the same reason. Nobody expects us to live under water so we should not expect Concord roots to function in waterlogged soils either. When a soil becomes waterlogged the soil microorganisms quickly use up the oxygen dissolved in the water, which does not leave any oxygen for the roots. The roots cannot move stored resources and they cannot take up nutrients from the soil, most noticeably nitrogen. That is why waterlogged Concord vineyards in the belt have sparse yellow growth in the spring.
Waterlogged vineyards need to be drained from one of two water sources. Water from a high water table or excess surface water that does not drain fast enough from the root zone.
If a high water table is the problem, artificial drainage is needed to lower the water table. Although Concord roots mostly spread, there are roots that will go deep into the soil profile. The objective is to have as few roots as possible in standing water so the deeper the water table the better. If you think that a high water table is your problem then contact the outfits that install drainage tile. They are more knowledgeable and better equipped to deal with the problem. One thing to keep in mind is that this type of extensive artificial drainage could be expensive and the best management decision may be to select a different vineyard site.
Surface drainage is a different issue. Surface water becomes a problem when a soil layer somewhere in the upper soil profile does not allow water to drain through it fast enough. In this case, 'cracks' or 'channels' in the problem soil layer must be created for the water to drain through at a faster rate. I would like to emphasize that the natural soil pores are not good enough to drain the water at an acceptable rate and that larger pathways for water are needed in this situation.
Management now depends on the location of the problem soil layer. If the surface layer is the problem, such as in areas where silt deposits clog up soil pores, soil management may be the solution. Preventing mud and water from entering the area, planting a cover crop to improve soil tilth, or (dare I say) light cultivation may improve surface drainage. As some of you know, I am not a big fan of repeated cultivation because it cuts shallow grape roots, it burns up needed organic matter, and can worsen surface soil compaction in the long run. We have had better success in the Lake Erie region with no-till methods. Some Canadian growers have tried planting a thick tap-rooted plant, like wild radish, in the row centers to break up surface soil layers.
If compact subsoil is the problem, deeper plowing or subsoiling may be needed to get under and break up the compacted layer. In my mind, subsoiling to improve drainage and subsoiling to root prune are too different things. Unless vigor control or reduced photosynthesis is desired (which is almost never the case in our Concord vineyards) root pruning should NOT be a vineyard objective. However, if subsoil waterlogging is preventing healthy root growth, subsoiling to improve drainage should be a vineyard objective. In the latter case, subsoiling is probably not cutting off very many grape roots to begin with. Some growers have talked to me about subsoiling every other row every other year. I think this is too often for normal vineyard operations. If drainage is that big of a perennial problem in your vineyard than you may want to think of an alternate drainage method.
"For subsoiling to be successful, the subsoil shoe must lift the soil above it in such a way that the force of lifting produces the maximum number of cracks spreading out as wide as possible. Further, if the benefit of subsoiling is to last, the cracks must be stable for as long as possible. This means that subsoiling is best carried out when the soil profile is just moist or not too dry, which means that it is best done in years when the autumn is dry" (E. W. Russell, 1973, Soil Conditions and Plant Growth, p.801).
If the drainage problem is still deeper in the soil profile, artificial drainage in the form of tile, ditches, or moles may be necessary.
There are many advantages of adequate drainage, either natural or artificial. Improved aeration of the soil leads to more extensive root growth and activity. Root cellular respiration increases resource remobilization as well as nutrient and water uptake. Soil microorganisms that are important for nutrient availability also benefit from soil aeration. A deeper grape root system will help the vine withstand dry or drought conditions later in the growing season. A larger Concord vine with larger leaf area, crop, and root system will extract more water from the soil profile. This, in turn, may help create or stabilize cracks in a heavy soil that will be needed for adequate drainage later. There have been some instances in our region where subsoiling was done once, improved drainage, increased vine size, and was not needed again. Better drainage and root growth also helps prevent soil compaction. Lastly, well-drained soils are less likely to heave and break grapevine roots during the winter freeze and thaw.
As you are walking through your vineyards this spring, identify both the location and severity of poorly drained soils. A little standing water here or there may not be a big problem and may dry up or drain before any serious problems set in. However, if your roots are drowning, identify the source of the poor drainage and apply the proper management -- most likely in the fall. If subsoiling is required, do it in an effort to improve root growth through drainage and not in an effort to stimulate root growth through root pruning, it does not work that way.