OLYMPUS DIGITAL CAMERAby Sanne Kure-Jensen
In the eastern United States, soils are generally fertile and vineyard managers mainly focus on disease management. Soils are the basis of plant fertility and play a large part in determining vine and crop potential.
Speaking at a risk management workshop hosted by Greenvale Vineyards, Cornell University Viticulture Extension Specialist Hans Walter-Peterson shared his experience with an audience of vineyard owners and managers, extension staff and hobbyists.
Soil conditions
Like all Extension Specialists, Walter-Peterson said, “Start with a soil test.”
He urged growers to improve soil structure, pH and fertility before planting a single vine. Spend 1-2 years preparing the vineyard site. Amend soils as needed, add compost and grow cover crops to build organic matter. These unproductive years will be rewarded in increased future yields. Incorporate micro and macro fertilizers as needed for your grape variety needs. Turn lime, organic matter and other amendments deep into soils to reach the full functional root zone.
Lime moves slowly through soils. These amendments are very difficult to incorporate deeply after planting vines. Walter-Peterson likes to spread all amendments across the whole vineyard, including the space between the vine rows to prevent the vine roots to reach a less fertile zone and stop growing.
Compacted soils limit root growth in many ways. Water, oxygen, nutrient infiltration and organic matter will all be limited in compacted soils.
Fertility
Walter-Peterson said roots are more efficient than leaves in nutrient uptake. Be sure to adjust soil pH and amend soils per test recommendations. Work toward a soil pH of between 6.5 and 7 for ideal nutrient availability. Vine roots should have access to all necessary macro and micronutrients. Vines typically need almost twice the amount of nitrogen and potassium as they need calcium. Vines utilize lesser amounts of phosphorous and magnesium. Vines and yields will suffer without small amounts of these micronutrients: iron, boron, manganese, copper and zinc. When adding micronutrients, Hans urged growers to add only the ones soil and petiole tests show you need as vines can develop problems from over abundant nutrients as well as deficiencies.
Pruning and fruit harvest remove nutrients from plants. These can be replaced either through nutrients already available in native soils or soil amendments. Spreading composted pomace and shredded vine trimmings on vineyards does return some nutrients to soils.
Only apply nitrogen-based fertilizers as needed. Most of the vines’ nitrogen needs each year are supplied by reserves stored in the permanent parts of the vine (thick roots and trunks) from the previous year and from the breakdown of organic matter in the soil. Each percent of organic matter reported from a soil test will provide about 15-20 lbs of nitrogen without adding any fertilizer. Large Concord vines grown on low organic matter soils only require the equivalent of about 50 lbs/acre of actual nitrogen as fertilizer. Most vineyards will require less.
The amount of potassium lost by harvesting a crop is equal to five times the tons/acre of grapes harvested. If fertilizing with muriate of potash, use 1.4 times the pounds lost per acre to determine how much fertilizer to apply. If using a different material, check with the supplier to determine how much potassium each pound of the fertilizer will supply.
After a large harvest year, vines might exhibit potassium deficiency the following year. What defines a large harvest will vary with the type of grape. For example, a large harvest for Concord grapes might be 14 tons/acre and for Riesling grapes may be more like 7 tons/acre.
Calcium needs are typically two-thirds the level of potassium needs and half the level of nitrogen needs.
Overuse of fertilizers in agriculture have been linked to algal blooms and other water quality problems. Walter-Peterson recommended growers be proactive and make sure to use minimal, well-timed fertilizer application. Growers can save money by using only as much fertilizer as needed. Apply fertilizers only when vines are ready to take it up.
Plants make early season growth using the previous fall’s reserves in their roots. Vines will not take up much fertilizer until soil temperatures rise and new, fine roots are developed.
Urea is easy to get and a good source of nitrogen. Only apply urea in cool, dry weather to minimize the risk of volatilization. In high alkalinity soils like those in the Midwest, the risk of volatilization is especially high.
Nitrogen sources
Weatherization breaks down rocks in soil and makes certain elements, like potassium, available for plant root uptake. Legume cover crops, like clover, fix and store atmospheric nitrogen. When turned under, soil organisms convert the nitrogen in cover crop residues and other organic matter into forms that are readily available to the vines. Cover crops provide other nutrients as well, and increase organic matter, which aids in soil water retention and drought resistance.
Walter-Peterson recommended against planting clover between vine rows. Clover may provide too much nitrogen and unnecessary vigor. He encouraged planting grasses, which could out-compete weeds.
Save money and protect water quality by putting on half as much nitrogen as recommended in typical soil tests. Apply nitrogen-based fertilizers around bloom time while plants are growing fine root hairs for maximum nutrient uptake. To minimize fertilizer leaching or runoff, do not apply fertilizers just before a heavy rain is predicted.