Measuring vine nitrogen uptake after a wet winter
Coming out of a long period of drought, many vineyards have expressed optimism about the impact of the rain on yield and groundwater levels. However, there are reasons to be cautious, especially about the dynamics between water supplies, leaf area development and nitrogen uptake.
The abundant rainfall we received over the past month has already had visible impacts on key milestones, delaying pruning and bud break for many vineyards.
Water and nitrogen
As we discussed earlier this week, a wet winter at the beginning of a vintage like 2017 might induce a high level of nitrogen mineralization in the soil. In other words, the rate of conversion of mineral nitrogen into plant assimilable nitrogen is supposed to be higher this year than after a drought like in 2014.
Thus, high water supplies combined with ample heat and sunlight can facilitate both foliar development and nitrogen uptake. However, we don’t know if higher water supplies will stimulate in equal proportions foliar development and plant nitrogen uptake. In fact, high water supplies could increase proportionally more leaf area development than root nitrogen absorption. When this situation occurs, we observe counterintuitive trends: as canopy develops more than usual, nitrogen concentration gets more diluted into a larger volume of leaf area, even if nitrogen supply is not limiting.
In simpler terms, we know that 2017 conditions are favorable to high amounts of nitrogen and strong vegetative growth. However, even if we expect a more vigorous foliar development, the concentration of nitrogen per leaf area may end up being lower.
As we discussed in the last blog post, seasonal variations in leaf nitrogen content will directly affect the amount of vine water needs on a daily basis (i.e. the plant-based crop coefficient). As of today, we don’t know to which extend a larger leaf area development will affect this year’s crop coefficient once canopy size is set.
Is a larger leaf area going to increase vine water needs, even if nitrogen concentration per leaf area is lower? Or is a lower concentration of nitrogen per leaf area going to reduce vine water needs? Nobody really knows. The only way to characterize seasonal effect on crop coefficient variation is to capture plant-based responses using tools such as Sap Flow sensors.
Managing nitrogen uptake
Several solutions are available to address vine growth problem due to sub-optimal nitrogen uptake. Vineyards carefully balance the growth induced by high nitrogen levels with cover crops, drainage systems, and canopy management techniques. Finding the right approach and amount of application, however, requires the ability to track nitrogen levels at a more granular level.
This is now possible with Dualex, a new offering by Fruition Sciences. The device enables vineyards to take frequent measurements of leaf nitrogen throughout the season instead of relying on traditional leaf petiole analyses only done twice a year.
With frequent Dualex readings, vineyards can develop a nuanced understanding of nitrogen uptake and adjust their fertilization and pruning practices accordingly.
Which best practices do you know about managing nitrogen levels following wet winters? Share with us!
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 and when it’s needed. Dualex recently won the 2017 Wine Business IQ Innovation Award. Our Physiocap product helps growers identify where biomass accumulates in your vineyard to improve pruning and fertilization decisions. Our Sap Flow product helps to track seasonal effect on crop coefficient variations.