Following the timing of vine nitrogen absorption

grape-leaves-vineyard

Nitrogen absorption is one of the key contributors to vine vigor and fruit quality. While nitrogen deficiency can limit vine growth, excessive nitrogen could lead to problems such as excessive shoot growth and shading.

Nitrogen absorption mainly happens in two phases: between flowering and veraison and in the fall. Getting the absorption timing right enables winegrowers to fertilize when the plant needs the nutrients most. It is now possible to measure at the plant level what’s happening during the first phase of root nitrogen absorption. Nevertheless, the second phase of absorption is still not well understood and is currently investigated by many researchers worldwide (for instance by Celette et al., 2013).

The tracking of nitrogen absorption time profile is important from the viticultural, winemaking and financial perspectives.  

The vineyard manager’s perspective

Vineyard managers want to make sure that the vines have the right amount of photosynthetic activity. While the canopy architecture plays a direct role at intercepting more or less light, thus regulating up or down the photosynthetic activity, climate differences between seasons will directly affect the concentration of nitrogen for any given canopy architecture. In turn, variations in nitrogen concentration for the same leaf area exposed to light will drive up or down the photosynthetic activity. Dry vintages like 2014 in California likely induces a poorer nitrogen uptake for a given vineyard site, while wet vintages cause higher nitrogen uptake like 2016 in California.

At this point, it is important to keep in mind that plant photosynthetic activity and water use are related. Thus, for a given level of leaf area exposed to light, seasonal variations in leaf nitrogen content will directly affect the amount of vine water needs on a daily basis. (ie. the plant-based crop coefficient). In other words, for a same vine size, maximum vine transpiration will fluctuate according to the level of nitrogen uptake early season.

Two practical consequences for the vineyard manager are:

  1. The amount of nitrogen absorbed by the plant before veraison influences the water consumption during the season.
  2. For the same plant size, whether seen from the ground or from an aerial view, the amount of water needed to satisfy vine water needs will vary across seasons. Irrigation will have to be adjusted accordingly.

Low  nitrogen supply vs healthy vine (source)

The winemaker’s perspective

From a winemaker’s perspective, if you are producing rosé or white wines, you want to avoid nitrogen stress because it would result in a decrease of aromas. A 2005 study by Peyrot des Gachons et al., demonstrated that Sauvignon Blanc grapes express best aroma potential with a moderate nitrogen supply and less aroma with nitrogen deficit. The positive impact of foliar nitrogen on Sauvignon Blanc’s aromatic expression was also reported by Lacroux et al. in 2008.

On the contrary, if you are working with red varietals, you will look for a moderate nitrogen deficit. This is because zero nitrogen deficit results in a reduction in color accumulation and aroma complexity.  Hilbert et al., 2003, studying Merlot, showed that nitrogen levels have implications on the synthesis of anthocyanin, a key indicator of wine quality. More specifically, higher nitrogen supplies lead to delayed fruit maturation and lower skin anthocyanin content, which may be undesirable to some growers.

Recently Helwi et al, 2015 demonstrated that vine nitrogen status does not have a direct impact on the green-pepper aroma in grape berries and wines. These new findings clarify the confusion regarding what was thought previously:  Nitrogen has a direct effect on green-pepper aroma. Thanks to this study, we understand now that it is in fact the modification of bunch-zone microclimate, induced by the higher vigor of high nitrogen status vines, which is the culprit.

The financial perspective

From a financial perspective, it’s important to consider the negative impact of nitrogen deficit on yield. A strong nitrogen deficit in one season will reduce yield in the next season, according to a study by Guilpart et al, 2014.  Being able to gauge nitrogen uptake before veraison also enables vineyards to sustain their productivity.

Moreover, monitoring the time profile of nitrogen uptake during that critical pre-veraison phase improves the efficiency of fertilizing activity. For many vineyards, this may translate into a significant saving in fertilizer costs.

Fruition Sciences offers a full suite of products addressing a variety of vine health monitoring needs to enhance fruit and wine quality. Our DualexⓇ Signature product provides detailed nitrogen accumulation profile so that vineyards can apply fertilizer where it’s needed. Dualex recently won the 2017 Wine Business IQ Innovation Award.  To tease apart the effect of nitrogen vs. microclimate on green-pepper aroma, our Terraclima product analyzes the effect of topography and canopy structure on cluster climatic environment.

Posted by Vintage Report

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