There are unmistakable signs that grape aroma, even in renowned terroirs, is deteriorating, while at the same time the susceptibility of vines to disease is continually calling for new pesticides. Against this background, European wine-growers are beginning to rethink their strategies, questioning established conventions, re-discovering the ecological context of their work and adopting a “back to the roots” strategy based on the natural principles governing terroir quality.
The core principle underlying the new methods used in quality-driven wine-growing involves specifically promoting biodiversity. Though the visible signs of this shift – a carpet of fragrant flowers covering the vineyard – are not insignificant, the main aspect of the new methods is an understanding of a vineyard as an ecosystem whose ecological balance is dependent on a complex network of biological diversity. The presence of large numbers of butterflies, beetles, bees and birds are the visible signs of the whole system being in balance. The core factor lies however in the soil. The biological activation of soil life is the key to a stable wine-growing ecosystem. Soil biodiversity is the decisive factor behind terroir quality and a vine’s resistance to disease.
Vines are not machines converting NPK fertilisers into grape juice, and in doing so extracting a few trace elements from dead rock. They are instead living organisms dependent for their well-being and prosperity on their symbiosis with numerous other organisms. The energy created by a vine through photosynthesis is not just used to produce leaves, grapes, new shoots and roots. Some 30% of it is also used for producing root exudates, the function of which is to supply a fully-grown vine in healthy soil with up to 5 trillion micro-organisms (more than 50,000 different species, for the most part bacteria, fungi, protozoa and nematodes), from which it receives in exchange for carbohydrates important mineral nutrients, water and protection against parasites.
When this complex and extremely diverse network of micro-organisms in the rhizosphere of the plants is destroyed or permanently weakened by herbicides, pesticides, fertilisers and tilling, the vine’s entire biological system loses its balance. This in turn results in increased susceptibility to parasites and other pathogens (e.g. nematodes and mildew), reduced resistance to negative environmental influences (in particular water stress and nutrient shortages), lower life expectancy (a vine’s average life expectancy is 100 years), as well as the loss of the wine’s bouquet.
Characteristic terroir wines can only develop when the vine’s roots are able to uphold their symbiotic interaction with the wide range of species found in the soil and enabling the vine to organise its own nutrient system on the basis of a wide range of different nutrients.
A vine reigns over the microflora in its rhizosphere like a king over his kingdom. For this ‘kingdom’ to be established however, the requirements for a stable nutrient cycle need to be fulfilled throughout the soil system. Earthworms, arthropods, bacteria and fungi need a steady diet of organic matter (leaves, straw, twigs, branches, roots, bones, faeces, meat, exudates) which they decompose before storing and distributing them in the soil. Where this diet is not available – with spraying having killed off most of it, with soil ploughed up and compacted by tractors and/or when nutrients have been eroded and leached out of the soil -, soil life becomes doomed to a slow death.
To promote soil activity, a plethora of different plant species is required. Their different contents and life cycles are needed to supply the soil with nutrients throughout the year, thus stimulating soil activity. This is the reason why a large number of ‘companion’ plants are needed alongside the vine, not just providing green cover and protection for the soil, but also fulfilling the following functions:
- Building up humus;
- Distributing nutrients, aerating the soil and protecting it against erosion through roots spread out in all directions;
- Storing mineral nutrients through symbiosis with bacteria and mycorrhiza; producing natural fertilisers (in particular nitrogen and phosphorus) available to plants;
- Producing secondary phytochemicals important for balanced soil health;
- Increasing the soil’s capability to store water;
- Degrading and adsorbing toxic substances in the soil;
- Promoting insect diversity through flowers and leaves.
In accordance with these criteria, the Delinat Institute has developed a range of seed mixtures tailored to different types of soil and climate conditions. Over the last 5 years, these have been tested in different vineyards, looking at the effect they have on vines, wines and the ecosystem in general. The seed mixtures contain some 40 – 50 different plant species, whereby the majority are legumes with varying root lengths and growth rates (alfalfa, red clover, common sainfoin, birdsfoot trefoil, hop clover, vetch and vetchling).
A meta-study on the effects of cover crops in vineyards has shown that these are practically nearly all positive with regard to reducing pathogens on vines. Vine health can thus be boosted and with reduced use of pesticides, grape quality can be influenced positively.
Through reduced pathogen pressure, vines become able to steadily improve their immune systems. This in turn allows further reductions in the amounts of pesticides needing to be sprayed, in the best case creating a self-reinforcing virtuous circle. An improved immune system leads to the increased production of secondary phytochemicals, again having a positive effect on grape and wine quality.
Where the vineyard soil is rich, selected cover crop strategies can help establish healthy competition, thereby regulating yields and improving grape quality. Induced moderate shortages force the vines to develop partnerships with soil micro-organisms (e.g. mycorrhiza fungi or rhizo-bacteria). These in turn can improve the availability of energy-rich nutrients. The result is an autonomous and, insofar as the right balance has been achieved between moderate stress and improved soil fertility, balanced diet for the vines, again having a positive effect on grape quality.
Stay tuned for Part two where we will share about ecoysystems, how to build biodiversity and its economic benefits.
Have you seen the cover crops growing at Everflyht Vineyard?