Spring is the time of bud break. The new growth erupting from the dormant vines shows that a new cycle of growth has begun. This is a critical period for the vines and it is vital to ensure that they have access to the right nutrition to lay the foundations for a successful season. In this month’s Vineyard Magazine, we take a look at the changing nutritional needs of the vine throughout the growing season and look at how some of the current research around the world is exploring how growers can give their vines the very best chance by using the best nutrition management strategies throughout the year.
The nutrients required by a vine vary depending on the time of year and the stage of growth that the vine is experiencing. This gives us a calendar of nutrition that can assist in supporting the development and growth of the vines and their crop.
From dormancy to budbreak
In this first part of the season, it is key to promote the strongest possible early growth, both of leaves and buds. To this end, nutrients including Nitrogen, Potassium, Calcium, Boron, Zinc and Iron are key during bud break.
For consistent productivity and maximised photosynthetic activity, Phosphorus, Magnesium, Sulfur and Manganese play an important role in plant development during the spring. Molybdenum complements this by offering the best possible inflorescence development.
Recent research in China’s Ningxia region showed that the uptake of Boron peaked during flowering and therefore applying it at this time could improve root growth and fruit set rates. Previous research from Brazil in 2022 had already shown how Boron is abundant in the vine’s flowers before gradually concentrating in the grapes themselves during the berries’ development.
The berries set, swell, and veraison begins
While Nitrogen is key for a strong set and that early grape growth, maintaining healthy berry development falls to Calcium, Iron, Magnesium, Boron and Zinc. Potassium plays a role in the early part of this stage by helping to maximise the growth potential of the grapes.
A combined application of Calcium and Iron enhances photosynthesis as well as encouraging increased berry size, weight and yield, in comparison to a single application of either, or none at all. A balanced supply of these two elements enhances the sugars, amino acids and flavonoids in grapes.
Veraison is completed and the grapes are harvested
Improving crop potential is key during this phase. Nitrogen is important here and also plays a role in grape colour. Boron can help to improve the size and shape of the fruit, as well as their sugar levels – which Potassium, Zinc and Iron also make an important contribution too.
For a healthy crop, consider Calcium’s role in warding against fruit diseases. A grapevine that is deficient in Calcium may exhibit a brown discolouration on the grapes, and rot can set in from the tips. Following this the grapes will begin to dry out. Magnesium is used to reduce the likelihood of bunch stem necrosis. Here, a deficiency in Magnesium begins as a hollow necrosis of the stalk before later the grape skin breaks down and the pulp becomes watery.
Post-harvest
As the vines prepare once more for dormancy, Nitrogen helps vines to build their carbohydrate reserves. Phosphorus will benefit the root system and Calcium will boost the lignification process that keeps the vines hardy over the winter. Calcium is a constituent of the cell wall which explains its significance in wood maturity, which will in turn help to give the vine a greater tolerance to frost. Calcium also gives the cell wall elasticity, which can minimise cracking and splitting of the wood at the end of the growing season.
Current research
Around the world, researchers continue to innovate in the field of vine nutrition, putting best practice to the test in order to grow healthier, more resilient vines that are capable of producing the best quality wines.
Cold hardiness
In the Michigan State University’s Department of Horticulture, Paolo Sabbatini has been sharing the work of the late Imed Dami of Ohio State University, disseminating his research-driven approach to management strategies for cold hardiness. His work focused on getting vines ready for winter dormancy in order to improve their health and productivity in the next growing season.
Imed Dami’s research has highlighted the importance of carbohydrate storage in the roots, trunks and canes of the vine during their winter dormancy, which not only help them to tolerate cold (the sugars act as cryoprotectants) but also allow for uniform regrowth when the spring arrives.
A number of tips for best practice relating to vine nutrition have been suggested by the research:
- Nitrogen management – it is recommended that nitrogen fertilisers are not applied after mid-summer to avoid stimulating late-season growth. Too much nitrogen delays the lignification process where the vine tissue hardens into bark, which can leave them susceptible to damage during the cold temperatures of winter.
- Cover crops – the improvements that cover crops like rye, clover or legumes offer to soil structure and microbial activity are highlighted as an important part of cold hardiness.
- Soil insulation – using an organic mulch around the base of the vine is recommended to insulate the roots and protect the vulnerable graft union from freezing temperatures.
- Post-harvest nutrition – Imed Dami highlights the role of post-harvest nutrition’s role in helping the vines to build up those all important carbohydrate reserves in preparation for the onset of winter. He recommended applying fertiliser before leaf fall to give time for the vines to absorb nutrients effectively. To this end, tools like soil testing and satellite systems are suggested to ensure that fertilisers are applied with maximum precision to ensure optimal nutrition and minimal waste.
Late season leaf health
A study in Australia has been examining the way that wine quality is impacted by late season leaf health. This piece of work charted distinctive vigour zones within a vineyard that offered the opportunity to record leaf health gradients.
Leaf health was manipulated with nitrogen fertilisers in order to measure the impact it had upon the quality of the resultant wines. As you might expect, healthier leaves were linked to a greater overall canopy growth and a more dense canopy, with leaf and must nitrogen levels also being higher than the control.
While fruit sugars were unaffected by the improvement in leaf health, it was seen that acids rose and tannins decreased in wines where the leaf health had been purposefully improved. Interestingly, the project found that the sensory preference was for wines made from the fruit from vines with less healthy leaves and lower vigour, with little obvious sensory difference from those ‘benefiting’ from the nitrogen addition.
It seems that this could be an area for further study in order to be able to draw more useful conclusions about actively manipulating leaf health.
Does vine nutrition impact wine?
A 2021 study from the University of Massachusetts explored whether macronutrients, micronutrients and toxic elements are transferred from soils to grapes and into commercial wines by analysing samples from five US vineyards.
Their work suggested that only Calcium, Potassium and Magnesium were added or retained from the grape berries themselves through to the finished wine. The concentrations of all other micronutrients and the toxic elements Arsenic, Cadmium and Lead were diminished during the winemaking process.
Interestingly, they found that soils, geology and climate do not generate a unique geochemical terroir, as the transfer and concentration of inorganic nutrients was roughly comparable across the vineyards, even though they were very different in soil composition and geographical location. As early as the 1980s, researchers were attempting to see if terroir could be analysed by measuring the influence of climate and soil on the quality of grapes and wines. This study suggests that the types and concentrations of nutrients found across any given wines might be roughly comparable.
They also showed that while the toxic elements found were below the standards set for drinking water, they were at “non-trivial” levels and the nutrient elements also had a potential impact for human nutrition, “as wine can meet or exceed the recommended dietary allowance of Ca, K, Mg and Fe, depending on the wine and the human consuming it.”
Meanwhile, a New Zealand study has attempted to determine the possible impact of using industrial hemp as a cover crop for grapes. It has been observed, for example, that Eucalyptus trees growing at distances of up to 100m from vines could have an impact on the resulting wines thanks to the transmission of 1,8-cineole, a volatile monoterpene (Eucalyptol), so researchers were interested to see if hemp was a positive influence on not just the soil, but on the wine itself.
The vineyard has poor soil so they were keen to see if the right cover crop could improve it.
Over three growing seasons, hemp was planted between grape rows (with a separate control section) to see how it might improve soil conditions as well as providing a secondary cash crop, since industrial hemp can be used in the production of a wide range of items.
They had to think carefully about what hemp to plant. It is hardy and fast-growing with deep roots, so the wrong genotype could actually compete too much with the grapes for light. The types used to make fibre grow too tall, so they chose the types selected for oil and seed, which grow a lot shorter.
Hemp is very drought tolerant, which makes for a good cover crop in drier regions. Even during a drought period in New Zealand during the study, the vines showed no signs that they were competing for water. A drawback of hemp, compared to some more traditional cover crops, is that it does not reduce pests as much. The absence of traditional flowers means it doesn’t attract as many beneficial insects that keep pests down.
It was noted that since the hemp was being harvested for a secondary income stream, most of the biomass was removed from the vineyard and not introduced to the soil. This limits the benefits the crop has on the quality of the soil – a key motivator for introducing cover crops in the first place.
The researchers were surprised to discover that the quality of the wines made from the test vines were superior to the control group, but this is anecdotal and more tests would need to be done to draw any firm conclusions about whether hemp can positively influence the flavour of wine grown alongside it.
Growing hemp in the UK requires a licence under the Misuse of Drugs Act (1971). Adding that administration to the logistics of managing a secondary crop, it is unlikely that UK growers will take the opportunity to experiment with hemp as a cover crop – at least not until further research has been done to prove the benefits.
Read more in Heavy Metal Environmental Contaminants in Food, a special issue of the International Journal of Environmental Research and Public Health printed in 2021: www.mdpi.com/journal/ijerph/special_issues/HMEC_F
Read the full paper on The New Zealand study: https://issuu.com/ruralnewsgroup/docs/final_hemp_cover_crop_trial_report_for_nzw
Taking organic to the next level
The ROC is an agricultural certification for soil health, animal welfare and fairness for farmers and workers that goes beyond the usual organic standards. It is managed by the Regenerative Organic Alliance, but there are currently no ROC certified farmers in the UK.
This is perhaps because there is currently no legal definition of ‘regenerative farming’ in the UK while the term ‘organic’ is tightly controlled and independently audited. As the term is being used more widely, the Advertising Standards Agency has issued some guidance about best practice surrounding ‘regenerative farming’ claims with the understanding that consumer awareness of the term is currently low.
In the US, ROC is more common, although numbers are not large. You can count on one hand the number of wine producers who have achieved this certification. The Robert Hall Winery in Paso Robles, California is one business that is actively working towards achieving ROC – they have demonstrated that all the criteria have been met and await the final paperwork. As part of the process they chose to initiate what is described as a ‘living case study’ to give the wider wine community the opportunity to learn more about the benefits of regenerative farming.
The three year trial was an industry first. The comparative study is set across 40 acres of their vineyards and compares all aspects of growing under regenerative organic viticulture versus conventional winegrowing techniques. They will be using organic farming techniques supplemented with biodynamic herbal and mineral composts and sprays. They are measuring the vineyard in a number of ways, including tracking organic soil carbon levels and soil microbiology, pesticide residues and pest & disease levels as well as assessing the sensory qualities, colour, tannin and phenols in the finished wines.
Satellite images and soil maps were used to ensure that the trial was like-for-like – using the same soil type and the same clone. The results exceeded their expectations; even in year one they were able to report noticeable changes. The regenerative organic block increased water retention by 13% in one year – a significant impact in a region where there is limited rainfall. Another key benefit was that the regenerative vines were more resilient when there were heat spikes in the area – a larger, healthier canopy was better able to protect the grapes in severe heat.
There was also a boost in microbial activity and the regenerative block scored 7.8 on the Haney soil health score, in comparison to 4.7 for the control block. The final harvest in 2024 showed a 15% increase in yield for the regenerative organic wines as well as an increase in wine quality.
There is a presentation about the full study available: www.shorturl.at/suO86
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