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From the Lake Erie Regional Grape Program Crop Update Addendum of 5/10/01

Tom Davenport Question:

We are getting questions on what the impact of the dry weather has had on the nitrogen that has been applied in the past 2 to 3 weeks. In particular what has been lost from volatilization with Ammonium Nitrate and Urea. Also, what growers should do if they have applied nitrogen during this dry period. Should they reapply some or wait till later around bloom to apply more. Also, what about the value of a foodgrade urea applied to the foliage now or later on.

Terry Bates Response:
Ammonium can be lost to the atmosphere, in the form of ammonia, but this can only happen under alkaline soil conditions and it is exaggerated during periods of light showers with strong drying conditions. Nitrate can be lost to the atmosphere as gaseous products through denitrification - the reduction of nitrates to nitrous oxide and free nitrogen gas. Denitrification increases in soils with a pH above 5.0 (with an optimum probably around soil pH 8.0-8.6), poor aeration (bacteria will only use the oxygen of nitrate when there is no free oxygen to use), and an active microbial population (which can increase with increasing organic matter). Therefore, alkaline soils that become waterlogged or have zones of high organic and anaerobic conditions; such as clods of manure, are at the highest risk of denitrification.

The majority of the vineyard soils in the Lake Erie Belt are acidic and well drained with relatively low organic matter. With the dry spring, many of our vineyards that are poorly drained and susceptible to waterlogging have not seen anaerobic conditions. Therefore, for the majority, we are at low risk for gaseous nitrogen loss. Will you loose some of the nitrogen that you put on your vineyard to the atmosphere and to leaching? Yes. Is it any more than any other year? Probably not.

What about N demand? About 5-10% of the total N that the vines will take up during the entire season will be taken up prior to bloom. 90-95% is taken up from bloom to leaf fall. Spring grapevine growth uses both stored N that was taken up last season and absorbed N taken up this spring. Although we have had a dry spring, there is plenty of soil moisture and available N in the rootzone of our grapevines to supplement the stored N that is in the roots, trunks, and cordons which will be used to build new shoots and roots in the pre-bloom period. Since we want most of our fertilizer N available after bloom, the lack of heavy rainfall this spring has most likely helped us by slowing down the rate of N leaching.

Sometimes we make too much out of N fertilization. Many studies have been run on the type, rate, split-application, and timing of N fertilizer application. All the studies show pretty much the same results. Over the long haul, zero nitrogen is a bad thing and will lead to reduced photosynthesis and vine growth but it does not kill the vine. We have 43-year-old Concord vines that have never received N fertilizer and they are still alive and producing a crop (not a very big crop but a crop). N fertilization is used to supplement and replenish soil derived N that is removed by grapevines. It is not used as the sole source of N for the vines throughout the year. Some N fertilizer is a good thing and too much is a waste of money and potentially bad for the environment. In the West Tier (gravel soil - 43rd season), 50 pounds actual N is adequate for optimum growth and production and 100 pounds is excessive. At the current N study on the Betts farm (clay soil - 5th season), 20 pounds actual N appears to be adequate where 70 and 120 pounds is possibly excessive.

What about foliar applied Urea? In my opinion (and it is just an opinion), foliar application of any nutrient should be reserved for certain emergency type situations. None of these situations apply to spring N uptake in Lake Erie vineyards. There is plenty of available N in the soil, you should have active roots this time of year (if you manage your vineyard properly), and the pools of stored N and soil N are enough to get us through fruit set and beyond.

The use, need, and efficiency of foliar nutrient application vs. soil nutrient application are the subject for a different article.

In summary: N fertilizer is expensive this year. Do apply N to your vineyard but think about running your own fertilization experiment in a small block this year or next where you reduce N application next to a block that gets your normal N rate. Continue with the treatments for several years to see if there is any difference in vine growth or productivity between the blocks. After you get the N on this year, forget about it and start calibrating your sprayer for your first pesticide spray.