Long-term organically farmed soils emit 40 percent less greenhouse gases per hectare than conventionally farmed soils. The amount of emitted gas is also lower per ton of yield or – in the case of maize cultivation – equal. This is the result of a study carried out as part of the DOK long-term field experiment.
The study was led by Dr. Andreas Gattinger, a former FiBL researcher, who is now a professor at Giessen University. The results were recently published in the online edition of the scientific journal “Scientific Reports”.
Agriculture accounts for around eleven percent of global greenhouse gas emissions. Soil emissions account for the largest share – most notably in the form of nitrous oxide. “While it previously had been thought that organically farmed areas emit more greenhouse gases per ton of crop yield, our study shows a different picture,” says Gattinger. “Organic farming contributes to mitigating climate change”.
Crop comparison since 1978
The study was carried out by the Research Institute of Organic Agriculture (FiBL) and the Swiss centre of excellence for agricultural research Agroscope in the DOK experiment in Therwil (Canton of Basel-Landschaft, Switzerland). In the DOK trial, the bio-dynamic (D), bio-organic (O) and conventional (K) cultivation of arable crops such as wheat, potatoes, maize, soya or clover grass has been compared since 1978 at the same site. Since 2012, the most important greenhouse gas in agriculture, nitrous oxide (N2O), has been determined in five cultivation systems in the crop sequence clover grass-maize-green fallow. These systems included two organic (bio-dynamic and bio-organic) and two conventional (with/without manure) farming systems as well as one unfertilised control system.
Bio-dynamic with the lowest nitrous oxide emissions
The result: The organically farmed areas had around 40 percent lower nitrous oxide emissions per hectare than the conventionally farmed field plots. In terms of yield, the “bio-dynamic” system had the lowest nitrous oxide emissions, the “zero fertilisation” control treatment the highest. The maize yield showed no difference in nitrous oxide emissions between organic and conventional farming.
“This proves that it is not only the renunciation of larger amounts of chemical fertilizers that leads to reduced emissions in plant production, but also the targeted use of diverse crop rotations and farm based amendments such as farmyard manure and slurry to maintain important soil functions,” the authors say. This finding is supported by the fact that important indicators of soil fertility such as pH value (acidity of a soil), organic matter in form of humus and microbial biomass in the soil correlated negatively with nitrous oxide emissions.
“With these findings, agricultural farming systems can be optimised with regard to their greenhouse gas emissions,” the authors say. The results of the study will now have to be transferred to different soils, regions and cultivation systems through further long-term studies.
The work for the study was supported by the Swiss Federal Offices for the Environment (FOEN) and Agriculture (FOAG), the Mercator Foundation Switzerland and the Swiss National Science Foundation as part of the National Research Programme Sustainable Use of Soil as a Resource” NRP 68.
This news is based on the media release “Ökolandbau mindert Klimawandel”, which was published by the Justus Liebig University Giessen on 14 March.
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