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Prof. Dr. Randolf Kauer Prof. Dr Randolf Kauer is professor of organic viticulture at the Geisenheim University of Applied Sciences and winemaker in Bacharach on the Middle Rhine. Together with Dr Johanna Döring and other scientists, Kauer has been supervising a comparative trial of organic, biodynamic and integrated cultivation since 2006. The findings show: Organic viticulture can be the answer to drought stress. However, the problem of fungal diseases still exists.

For 16 years, the Geisenheim researchers have been investigating plots of land in a trial with four field replicates, which - strictly separated from each other - are cultivated conventionally according to integrated standards, organically and biodynamically. The difference between the latter two variants is mainly in the application of the biodynamic preparations horn manure and horn silica and the compost preparations. The greening mixtures in the organic variants are the same - and more diverse than the grass-dominated mixture of the integrated plot. Shortly after the start of the trial, both organic variants showed lower vigour and yields. Lower woody yields are desirable because they create a loose and airy foliage wall.

Organic adapts better to drought.

A few years after the conversion was completed, the researchers noticed other effects: Changes in soil, organic carbon storage, enzyme activity, community composition. In the four hot and dry vintages after 2017 (with the exception of 2021), "changes occurred that we had not expected and had not observed before. They have to do with the reaction of the different systems to the drought," explains Dr Johanna Döring. For example, the yields of the integrated and organic variants converged, which had always been higher in integrated cultivation before (see figure). In 2018, 2019 and 2020, the organic plots even had higher yields in some cases. "In 2018 we were still surprised, in the meantime we are convinced that these are not coincidences and that these systems have adapted better to the drought. Something is causing the organic variants to behave differently than the conventional ones," Dr Döring notes. In addition, they examined cell wall strength and robustness of the plants to low water potentials. Both were significantly increased in the organic variants. Kauer sums up the findings: "The evidence is strengthening that organic management allows better handling of drought stress. Plants seem to adapt better to drought over a longer period of time due to the establishment of the diverse green cover."

Döring et al.

A comparison of the yields of the three variants. Green: biodynamic, blue: integrated, yellow : bio-organic.

Yields are one thing, quality is another. The nitrogen supply, which is essential for the development of aromas and yeast nutrition, is better in organic cultivation due to the input of legume-rich greenery. Phenol formation is also higher in the organic varieties, which Prof. Kauer explains with the more permeable structure of the leaf walls: "The grapes form more flavonols in the berry skins because they are better exposed." Overall, the sugar production and thus the potential alcohol yield in the organic varieties did not differ from integrated cultivation. This effect has already been confirmed by many other organic winegrowers.

Piwis are in demand

Dr. Johanna Döring
©Steffen Böttcher

So is organic cultivation the salvation? Kauer has clear ideas: "In order to implement the EU's Green Deal regarding the reduction of pesticides, we can only make progress if we rely heavily on Piwi varieties." Breeding has become much faster, he says, because the location of the resistance genes on the chromosomes is known. It is no longer necessary to test this for years in field trials. "In any case, we can only make the big leap with Piwis. In addition, we can also significantly reduce the use of copper with them, which is absolutely necessary. However, the use of piwi varieties is proceeding too slowly, even though the planting material is as good as sold out at the moment." He also has high hopes for individual greening management. "Of course, this is highly dependent on the water supply. In Spain, for example, I will hardly be able to get a continuous cover crop in summer, but in winter. So I get the nitrogen input into the soil there, too. The factors of biodiversity and nitrogen supply to the vines play a major role. Meagre grasslands and grass plantings are all well and good, but they cannot achieve these effects. That's where you already have, and where you can transfer a lot from organic to conventional viticulture in the future."

Johanna Döring takes up an argument that is sometimes heard: "Some people think: integrated cultivation has a higher yield. So I do integrated cultivation on 80 percent of my land and leave 20 percent fallow and dedicate it to biodiversity. But we can deduce from our observations that the integrated variant seems to lose the yield advantage under water shortage, because the yield differences no longer exist in dry years. In many parameters for the study of biodiversity, flora and fauna, the organic variants are clearly ahead - mainly due to the many types of cover crop."

Organic viticulture does not exist for free.

As a scientist and practitioner, Randolf Kauer also sees the disadvantages of organic farming. "Downy mildew sets limits for us. Combating this core disease with copper is indispensable. Only in very few locations can we manage without copper. If we always had dry years, it would help organic, but wet years like 2016 and 2021 bring huge yield losses. You have to be aware that there can be such conditions for several years in a row, and you have to be able to sustain that economically." In addition, there would be the higher labour input and the necessary clout in vine protection. "If you can't react quickly to certain weather situations, it becomes difficult. You need manpower for that. Organic farming is not free. It has great advantages for all of us, but for the individual farms it initially involves an increase in costs, which they have to price in. Organic is nice, but you also have to be able to live from it." Nevertheless, he would like to encourage his fellow winegrowers to try organic farming: "Have the courage to convert to organic! Make the experiences, even if they are sometimes negative. Organic farming requires a great closeness to the soil, the plant, the weather, the ecosystem, and this experience can be very enriching. We see the ever-increasing interest in this among our students. I wish my colleagues to open up to it, because the market demand is pushing us more and more in this direction."

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