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Farming through El Niño
Updated: 5 days ago
This upcoming season has been forecast with a strong El Niño, which means hotter and drier than “normal” in all of the major wine growing regions here in New Zealand. For many of you – this is not your first El Niño rodeo – but this time around there is an added layer of considerations with financial pressures for many vineyard operations. So, in the spirit of planning for the worst and hoping for the best, here’s some food for thought.
Simply a “hot and dry” forecast does not an El Niño event make
New Zealand has experiences some exceptionally dry and hot periods in the last 10 years, but technically the last declared El Niño Summer was the 2015-2016 vintage, as defined by NIWA/NOAA/etc. For a season to be classified as El Niño or La Niña conditions have to persist over a period of consecutive months, and this distinction is important to consider.
Thinking back to Summer 2018/2019 in Marlborough – which falls into the neutral category as far as ENSO events. The first half of the growing season was not too dissimilar to “average,” then January changed everything. There was almost no rain and at the end of the month, to make matters worse, there was a week or two with unusually hot temperatures. Irrigation cutoffs were across the board with hot, windy days, and six weeks between any substantial rain. You didn’t have to look too hard to spot the vineyards without a dam after that.
The vines had sufficient/plenty of water until they did not.
“Never let a good crisis go to waste” – Winston Churchill
The predicted super El Niño has been on the minds of farmers for some time now, and people are worried. Do we have enough water? Will we have enough water? What will harvest look like? This is all on top of financial and contract pressures across the industry.
When the pressure is on – and particularly when it can be classified as a crisis – those that maintain the status quo and hope everything will be fine are often left in the dust. So, while the rest of this blog will have themes of my standard message to growers, there are some considerations specific to worst case scenario. And hopefully this will be helpful to those looking navigate a dry season with an understanding that they may not be able to maintain the status quo because of outside forces.
Preparing for the worst
For North and Eastern New Zealand an El Niño Summer typically means warmer and dryer than average, but how far from average is yet to be determined.
“While we know the average outcome of El Niño because of historical data, no El Niño is average, each comes with a unique set of climate characteristics and therefore can be expected to influence the weather differently.” - NIWA
It’s therefore better to prepare for the worst and be pleasantly surprised. Considering our average temperatures in “normal” years are not even close to maxing out the vine’s capacity for heat, the true limiting factor growers need to prepare for is water.
Irrigation Infrastructure & Support Systems
If your site is irrigated - ensure your irrigation is functioning up to specs and that water delivery is what is expected. Lines should be flushed in the winter/spring as a standard practice, but it’s especially critical if the irrigation is going to be put under pressure. Make time for it.
If you’re working off of stored water, or may need to, ensure you go into the season with a full dam/reservoir, and that it doesn’t leak. These may seem obvious, but you’d be surprised how often the basics get ignored. Let’s move on to more interesting discussion about management and vine physiology.
Set the vines up for success
This might be reaching, but a forecasted El Niño event does provide lead up and a longer forecasted period that managers may be able to leverage while encouraging growth of resilient vines.
Root Systems Matter
It may seem counterintuitive to hold off watering to make the vines more drought resilient, but early and often sets are not helpful. One of the limitations of watering early is that it stops, or dramatically slows, any root exploration into the row or into deeper soil. Most of the nutrition is found at the surface, so vines always need roots in the shallow soil, however vines can also grow to substantial depths (soil permitting) if the surface soil dries out periodically. When irrigation is supplied early and often, the surface soil along the drip line becomes a source of both water and nutrition, and so roots proliferate in the topsoil, rather than having to grow downwards – regardless of rootstock selection. The vine channels more energy into growing shoots and less into growing roots.
In the early season, before appreciable canopy development, the vine’s water needs are small. This is the ideal time to allow the surface soil to dry and force the roots to grow outwards and downwards. Ideally, a pressure chamber or similar tool can be used so that water can be applied before bringing the vines to undue stress. Soil probes can also be used to track drying in the soil at various depths. Ideally, and again soil dependent, irrigation can be spaced so that the surface gets a chance to dry out between sets. This both reduces weed growth and disincentivizes all the root activity being at the surface.
Canopy Size Matters
A vine’s water requirements are determined by the weather and the vine’s canopy. I live in Sauvignon blanc country, where the standard is to grow a large and dense canopy. A large dense canopy is a manager’s worst enemy in any season – the challenges are slightly different when comparing dry vs normal vs wet season. For example:
Disease pressure
Required maintenance (e.g. extra trimming/leaf plucking)
Large internodes
Bud shading
Lignification delay
Yet, in a very dry season, trying to grow and maintain a dense canopy in the vineyard can add a self-inflicted risk of water stress. Many studies have looked into the amount of canopy needed to ripen fruit, and they all land in the 0.8 to 1.2 m2 leaf area per kg of fruit. More leaf than this does not speed ripening, but it absolutely speeds water loss. Going into a dry season where water limitations are likely, keeping these leaf area guidelines in mind, rather than aiming for a “normal” canopy is the best way to go.
Growing a big canopy through early and often irrigations will guarantee a large amount of water to maintain photosynthetic activity. If water becomes limited later in the season, these larger vines come to stress earlier and come to more extreme stress between irrigations that vines with smaller canopies. By holding off early irrigation, shoot and lateral growth are slower, meaning an overall smaller vine that needs less daily water. Remember, any more leaf area than 0.8 m2 doesn’t speed ripening, so a larger “solar panel” or ”engine” doesn’t necessarily speed ripening or increase berry size during ripening. What it always does, however, is speed water loss.
The Water "Bank"
I’ve heard growers talk of “banking water” in the soil. I won’t get into it here, but this logic is particularly bad in a dry year. From the vine’s perspective the temperatures are going to be optimum for growth, so that “bank account” will deplete, and in the process encourage canopy growth that may not be sustainable later in the season.
Management Strategies for El Niño
These by no means guarantee smooth sailing through the worst-case scenario, but they at least take advantage of opportunities that might not be present in a “normal” year.
Unlike 2019 – an El Niño Summer predicts an extended dry period, so encourage the vines to maximise soil exploration.
Do not start watering until the vines need it
Try longer sets with greater time in between them
Monitor water needs before watering
Pressure bombs and porometers can provide vine status which is the ultimate test
Calibrated soil probes – can help pay attention to the rate at the soil is drying OR wetting with irrigation sets
Long internodes & lateral growth post trimming probably means your vines have more than enough water
But what happens if the shit hits the fan?
So let’s say we get a similar situation to 2019, or you just haven't read this until the shit has hit the fan. Hot, windy days, irrigation cutoffs, and six weeks between any substantial rain, and your limited or even cut off from irrigation water. How does a manager stop the vines from defoliating and ruining wine quality with very limited water for prolonged periods?
Since the canopy is the source of water loss, cutting it back will reduce water use, allowing irrigation water or rain to sustain a vine for longer. In some of the low alcohol wine work we did here in New Zealand, 25% of a Sauvignon blanc canopy could be cut off without slowing ripening at all. While it was not directly measured, I presume this is because the vines still had 0.8 m2 leaf area/kg fruit with 3/4 canopy. This suggests we can substantially reduce the canopy height of our vines to reduce water usage without affecting ripening, especially for two cane and yield restricted vines. Even cutting Sauvignon blanc vines to half canopy only slowed ripening by a week or two compared with well watered full canopy vines.
A large canopy with completely closed stomata from water stress doesn’t ripen fruit at all, however. I suspect the story from the low alc work would have been very different under water restrictions, where the difference between half canopy and full canopy vines would be smaller. With limited irrigation rations, total vine photosynthesis before stress closes stomata could be substantially more from the smaller vines, which would maintain activity longer after watering. In fact, the half canopy vines might actually have ripened faster, especially if limited irrigation water was available from storage.
If you normally cane prune, cutting to a lower canopy height this summer might mean you have to do a year of spur pruning next season to maintain vineyard productivity. However, I feel this is a small price to pay to ensure your vines maintain leaf cover around the fruit so that they achieve the ripeness and quality standards to make ultra premium wine.
Final Thoughts
The variability in variations from "normal" across multiple ENSO events is exactly what you'd expect from a weather forecast - trends can be determined, but it's hard to know what a given season will bring. All you can do is leverage the information you have to make educated management decisions and think about what in your "normal" programme might set you up for failure in a super El Niño season - as is forecast.
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