Too little nitrogen and you can’t ripen a crop…too much nitrogen and you can’t ripen a crop, so it is no wonder that understanding how and when to use this powerful nutrient is one of the most fundamental aspects of successful vineyard management.
My good friend Paul Crout sat down with me recently to talk about all things nitrogen, and in today’s blog, I share some of the highlights of our discussion.
Paul is one of the foremost experts on vineyard nutrition and spray, a leading pest control advisor, and a Certified Crop Advisor. He is currently practicing these skills as an agronomist with Helena Agri-Enterprises in California. He creates fertility plans and holds training programs for growers across the country.
Nitrogen Sources
Convention nitrogen fertilizers typically fall into one of three forms – ammonium, nitrate, or urea. Which form or blend you use depends on the timing and condition of your vineyard.
Plants take up nitrogen primarily in the nitrate form, so a nitrate-based fertilizer is best used when a rapid uptake is needed and/or when soil microbes are not active to break down the fertilizer for uptake by the vines because of cold or excessive soil moisture.
Ammonium and urea-based fertilizers require soil microbes to break them down over time into nitrate form for uptake by the vines. These fertilizers are best used either when you want a slower nitrogen release or when weather conditions (e.g. soil is warm) are conducive for highly active soil microbes to rapidly convert the ammonium or urea intro nitrate form for vine uptake.
Organic sources of nitrogen are all-natural sources. Some examples of these are feather meal, crab meal, soybean meal, and fish emulsions. They are all generally in a protein source.
Proteins need to be significantly broken down in the soil and digested by soil microbes. They get broken down, released as ammonia, processed into ammonium, and then processed into nitrate. This process can take weeks or even months and during this extended time, only a fraction of the nitrogen is even released.
Using organic sources requires a systematic approach of planning and applying well in advance to ensure nitrogen availability for the vines’ peak demand timing. Organic growers need to focus on an ongoing year-over-year fertility program to build up nitrogen in the soil for continual nutrient availability to meet vine uptake demands.
Application Timing and Methods
Proper application timing is essential to ensure nitrogen is available ahead of peak demand, so vines can have adequate uptake for their highest demand period to maximize their growth and nutrition. In wine grapes, the period of greatest demand occurs around bloom. The target for most growers is to get 70-75% of their annual nitrogen budget to the vines before fruit set. Then, apply the rest of their nitrogen budget during the second demand period which is post-harvest.
There are three main methods for nitrogen fertilization application: foliar, ground-applied, or injection through an irrigation system. Choosing an application depends on timing, your method of vineyard management, and the size of the nutrient gap you are trying to address.
Injection of liquid fertilizers such as calcium nitrate and ammonium nitrate is the most common and easiest application method allowing for nutrient delivery via drip emitters directly to the vine roots.
If you’re a dry farmer, your strategy changes a bit. You can still do liquid through a stream spray under the vines and dribble on nitrogen that way. Alternatively, you can do a dry application and rely on natural precipitation to solubilize the fertilizer. The key with a dry application is to get it on earlier to give you a bigger window as uptake is much slower.
Additionally, if you use dry fertilizer, including organics or urea, always incorporate it into the soil. If it’s on the surface, it will volatilize off and blow away.
Foliar is often used as a method for closing small nutrient deficiency gaps in the post-bloom fruit set stage. Foliar can also be used strategically for late-season application to keep the leaves photosynthesizing. This can be a safe way to put nitrogen on at the end of the season.
Growers must also keep in mind that application strategies will vary greatly depending on the age and location of the vineyard and the weather conditions of each season. All growers should seek the advice of a vineyard professional and follow the product label – the label is the law.
Nitrogen Testing
Testing is important because both too little and too much nitrogen can be harmful in the vineyard. While too little nitrogen can impact the health and production of the vine and fruit, too much nitrogen can be damaging by causing too much vegetative growth, higher disease incidents and insect pressure, delays in ripening, adverse flavor components, and more.
Although soil tests will provide a soil nitrate number, this number does not provide an accurate picture throughout the season as the nitrogen levels change and fluctuate due to rain and vine usage. Soil tests are better used to provide an annual gauge of the nitrogen contribution available from organic matter as a starting point for nitrogen inputs for the season.
Whole leaf sampling is the best method to obtain an accurate status of the current nitrogen levels (as well as other nutrients) available to the vines. Plant tissue samples are best done pre-bloom or at bloom to allow time for corrective measures prior to peak nutrient demand for the season. The second sample time is at veraison to ensure adequate nitrogen (along with potassium) to ripen the crop.
If you want to learn more about nitrogen sources, application, testing, and more, check out vineyardundergroundpodcast.com/vu016.
