Vineyards as climate protectors

Soils are important carbon reservoirs on our planet. If additional carbon can be successfully absorbed by the soil, this could slow down climate change. Researchers from Bonn and Jülich are investigating whether wine-growing areas are suitable for this.

The metal cover is humming away quietly. The device, which is about 30 centimetres wide, is mounted on a plastic cylinder that protrudes a few centimetres from the dry soil of an idyllic vineyard in the southern Palatinate. After three minutes, biogeochemist Muhammad Islam grabs the cover by its handle and takes it off. On we go. He briskly pulls a silver metal box on four wheels along the vines to the next cylinder. Same procedure: put on the cover, wait three minutes, continue. The protocol is strict and the programme tight: five sections of the vineyard in Siebeldingen today, each with 24 measuring points.

Islam, a native of Bangladesh, is a doctoral researcher in Prof. Nicolas Brüggemann’s team at the Institute of Bio- and Geosciences (IBG-3), and his work is part of the VitiSoil research project coordinated by the University of Bonn. In the vineyard of the Julius Kühn Institute for Grapevine Breeding, Islam intends to find out whether additional carbon can be stored in vineyard soils.

„The idea for the project arose shortly after the Paris Climate Summit in 2015 on the occasion of an appeal by the Federal Ministry of Food and Agriculture.“
_{Prof. Nicolas Brüggemann}

Reducing the CO₂ increase

“The idea for the project arose shortly after the Paris Climate Summit in 2015 on the occasion of an appeal by the Federal Ministry of Food and Agriculture,” says Brüggemann. They were looking for ways to store carbon in order to counteract the increase in CO₂ concentration in the atmosphere. Soils could help with this. After the oceans, they are the largest carbon reservoir on our planet. Not only the climate could benefit if even more carbon were sequestered in the soil: the plants would also have more nutrients available for their growth.

Brüggemann explains that grape cultivation could be well suited to this approach: “Once a vineyard is planted, farmers don’t touch the subsoil for more than thirty years in some cases.” If soils are ploughed up frequently, as in the case of intensive use by industrial agriculture, they leach out over time. This also means that they store less and less carbon. The soils of a wine-growing area could – it is assumed – store the incorporated carbon for several decades.

Putting carbon deep into the soil

The researchers’ idea: to work organic, carbon-rich material deep into the soil of the vineyards instead of into the surface. At this depth, the decomposition processes of organic matter take place much more slowly as there is less oxygen available. This should significantly slow down the decomposition of the carbon contained in the material. The researchers also hope that the winegrowers could simultaneously save on inorganic fertilizers, which emit various greenhouse gases.

“To that end, we spread two different organic materials 30 to 60 centimetres deep in the soil at several locations in 2019,” Islam reports – compost at some spots, and a substrate that is commercially available and consists of compost and biochar at others. By mixing plant and food waste with charcoal, Islam knows, indigenous peoples in the Amazon region have already used a similar composition in their farming. They called it terra preta – black earth – and used it to increase the fertility of the rather barren rainforest soil. The possibility that such substrates could also increase winegrowers’ yields would be a positive side effect of the approach.

Regular measuring of CO₂ emissions

Islam travels to each location for three days, every other week. The metal cover tells him how much CO₂ the differently treated soils emit: “It measures the concentration of the gas in the volume of air above the respective cylinder,” he explains. His metal box contains the necessary technology. In addition, the researcher uses a sensor to determine the moisture in the soil and the air temperature at each stop. In this way, he receives indications of how, for example, the season influences CO₂ emissions.

Using a conventional syringe, Islam also takes air samples from different soil depths, which are then analyzed in the laboratory with the help of gas chromotography: “It could be that the incorporated organic material and soil compaction cause more methane or nitrous oxide to be released, which have a much higher global warming potential than CO₂,” says Brüggemann. However, the measurement results so far have not confirmed this fear. What the studies to date do show is that around one third of the incorporated carbon did not remain in the soil but was released into the atmosphere in the form of CO₂.

"Perhaps our results will help to influence agricultural policy in a way that mitigates climate change.“

Unexpectedly fast decomposition processes

“The organic material that was integrated into the soil was apparently not as stable as we had originally thought. The decomposition processes by microorganisms run faster than expected,” says Brüggemann. This could be due to the fact that there is more oxygen available in the soil than assumed. “This shows that things won’t be that easy. It obviously doesn’t work to simply put 30 or 40 tonnes of compost into a vineyard or a field,” the researcher draws a preliminary conclusion. An alternative could be to incorporate pure plant charcoal, which is much more stable than compost.

The measurements will continue until the end of the year. Muhammad Islam is not discouraged: “Perhaps our results will help to influence agricultural policy in a way that mitigates climate change,” he hopes. In any case, the researchers will pass on the project’s findings to policymakers by means of recommendations. For that, however, Muhammad Islam needs more results, and so he takes off the cover and moves on to the next measuring point.

Text: Janosch Deeg

Prof. Dr. Nicolas Brüggemann

Head of research group "Plant-Soil-Atmosphere Exchange Processes"

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Institute for Bio- and Geosciences - Agrosphere (IBG-3)

Sustainable use of the natural resources soil, water and atmosphere

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