The annual removal of crop and prunings also removes nutrients from the vineyard, depleting their availability within the ecosystem. Some vineyards rely on synthetic fertilisers to ‘fix’ issues related to nutrition. However, reliance solely on these applications creates a short-term feedback loop that can:
- Damage the vine’s natural mechanisms for obtaining nutrients from the soil because the vine no longer has reason to sustain symbiotic relationships between the vine roots and soil microbiome
- Fail to replace lost soil organic matter
In such cases, it becomes necessary to provide increasingly further inputs of synthetic fertilisers to sustain vine and grape development.
Within regenerative viticulture, an alternative or complementary approach is applied:
- Improve soil organic matter and use natural sources of nutrients such as those derived from organic compost
- Support the development of a symbiotic relationship between vine roots and microbiomes
Mineral nutrition is a major part of grape production, impacting all aspects vine growth, berry development and maturation, and ultimately juice composition as it relates to wine making.
The mineral nutrient requirements of grapevines vary according to the variety, whether the vines are growing on a rootstock, and on what rootstock that is, vine age and production levels. There is no single ‘recipe’. Mineral nutrients are removed by the crop and by removal of prunings, but the removal of some, e.g. nitrogen and phosphorous, is on a much larger scale than the removal of others. Some nutrients can be lost below the rootzone by leaching, and can also be lost to the atmosphere by a process known as denitrification.
Most of the biomass (shoots and leaves) produced annually by grapevines remains in the vineyard and releases mineral nutrients back to the soil as it breaks down. Mineral nutrients exist in soils in organic and inorganic forms in the soil solution, and bound up in organic matter. Where these are inadequate, or inaccessible to vines, fertilisers are commonly applied as supplements.
However, there are two fundamental issues with the use of fertilisers:
- Applied fertilisers do not replace lost soil organic matter
- Synthetic fertilisers can damage the plant’s ability to obtain nutrients from the soil
Understanding how the vine naturally obtains nutrients is key to understanding why you should be transitioning away from synthetic fertilisers.
When a plant photosynthesises, it converts CO2 into energy giving compounds. It uses approximately 60% for its own growth and shares the other 40% with microbes in the soil. In exchange for these ‘root exudates’, the microbes deliver nutrients to the vine in plant available form.
Some of these microbes are a type of fungi which grow into the root and then extend their filaments far out into the soil, reaching parts the vine roots could not reach on their own. These are called symbiotic myccorhizal relationships and plants form them as lifelong partnerships. Soil scientists describe these relationships as 1000s of conversations going on underneath our feet.
Synthetic fertilisers damage the vine’s natural mechanisms for obtaining nutrition from the soil. It no longer has a reason to share as many exudates with the soil microbiome and therefore the symbiotic relationships that the vine roots and soil microbiome have formed are compromised. It then becomes necessary to continuously provide synthetic fertilisers.
It is important to know what nutrients are in your vines and in your soil
Before planning any soil amendments, it is important to know:
- the nutrient status of the vine, through sap analysis
- the nutrients in the soil, through soil analysis
- which nutrients are not being taken up by the vine from the soil
You are then in a position to look at the causes of any nutritional deficiencies and non-synthetic fertiliser tools available to optimise nutritional uptake.
So, what are the tools available?
1. Add organic matter to the soil
Adding organic amendments to the soil in the form of compost or manure will increase the soil organic matter which in turn has the benefits of:
- Increasing the quantity and diversity of microbes in the soil
- Providing nutrients
- Improving soil structure and water holding capacity
- Acting as a mulch
Compost can be bought relatively cheaply as municipal compost. However, if space permits, compost should be made on site using vineyard prunings (if no disease pressure), winery waste, farmyard manure and other cheap, locally available materials. That way you know what has gone into it and you can tweak it to improve the ratio of C:N and fungi:bacteria. Widely used raw materials include:
- Vine prunings
- Press marc (with monitoring of potassium levels to avoid adverse effects)
- Grass cuttings
- Manure (check what the animals have been fed/vaccinated with)
- Biochar (note that biochar should not be added on its own)
Depending on what industry is nearby, examples of cheap, locally available materials could include:
- Brewers’ grains
- Citrus pulp (handily changing the acidity if that’s what you need)
Having several compost piles at different stages of decomposition is ideal. Soil analysis of each is essential to know the ratios of C:N and fungi:bacteria.
Increasing the microbial life inside the compost will improve soil health, sometimes referred to as inoculating the compost. This can be done following biodynamic principles, with worms (vermicomposting), or with a Johnson-Su bioreactor, etc. Compost teas can also be generated.
A side discharge spreader will enable you to spread the compost in the undervine strip. It does not need to be worked into the soil as the soil flora will do the job for you.
Other beneficial products such as liquid seaweed can also be applied and animals can be integrated into the vineyard to provide fertiliser through grazing.
Selecting and managing cover crops (see Cover Crops section) to maintain an appropriate nitrogen balance is also critical.
As it takes time to build or rebuild soil health, it is essential to have soils and petioles (or whole leaves) tested and to get advice from an agronomist to ensure there is an optimum nutrient balance for the vines’ growth and productivity.
2. Apply natural products
For example seaweed extract, or by making compost teas from plants growing in the vineyard.
The above practices can be complemented by not tilling your vineyard soils, instead leaving the mycorrhizal networks to rebuild themselves (see Cover Crops and Tillage sections).
- Compost https://rodaleinstitute.org/science/articles/a-scientist-shares-insights-and-tips-for-managing-compost-piles/
- Fertility through cover crops research Can cover crops replace synthetic nitrogen? | Wine Australia
- Using grape marc/pomace for compost GW September final low res.pdf (awri.com.au)
- Johnson-Su How to build a Johnson-Su bioreactor to produce your own on-farm biology – Farmers Weekly (fwi.co.uk)
- Biochar Biochar-October-2020-journal-article.pdf (awri.com.au)
- Vermicomposting https://rodaleinstitute.org/science/articles/vermicomposting-for-beginners/