Cropland farmed organically over a longer period emits less greenhouse gases per hectare than conventionally farmed soils. This value is also lower per tonne of yield or, in the case of maize crops, is at the same level. These results have been presented in a study on a long-term field trial that is the first of its kind world-wide and was headed by Andreas Gattinger, a professor at Justus Liebig University Gießen/Germany. The results have been published in the online version of the science journal “Scientific Reports”.
Agriculture contributes around eleven per cent of world-wide greenhouse gas emissions, with soil emissions, above all in the form of laughing gas, accounting for the largest share. “Whereas the dominant assumption used to be that organically farmed areas emit more greenhouse gases per tonne of plant yield, our study presents a different picture,” Gattinger explains. “So organic farming contributes to mitigating climate change.”
The examinations carried out in the context of this long-term trial comparing biological and conventional cultivation systems were carried out in co-operation with the Research Institute of Organic Agriculture (FiBL) in Frick/Switzerland and the Swiss Centre of Excellence for Agricultural Research in Zurich/Switzerland. In the so-called DOK long-term trial in Switzerland, the bio-dynamic (D), bio-organic (O) and conventional (K) cultivation of arable crops such as wheat, potatoes, maize soy or clover grass has been compared at the same site since 1978.
After a period of 34 years, the most important greenhouse gas in agriculture, nitrous oxide (N2O), has been determined in five cultivation systems. These comprise two organic (bio-dynamic and bio-organic) and two conventional (with/without manure) farming systems as well as one unfertilised control System.
The result was that the organically farmed areas had around 40 per cent lower nitrous oxide emissions than the conventionally farmed plots. In terms of yield, the “bio-dynamic” system had the lowest laughing gas emissions, and the “zero fertilisation” control treatment had the highest. The maize yield showed no differences in laughing gas emissions between organic and conventional farming.
“This proves that it is not only the renunciation of larger amounts of chemical fertilisers 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,” says study head Gattinger. This finding is supported by the fact that important indicators of soil fertility such as the pH value, organic matter and microbial biomass in the soil correlated negatively with the nitrous oxide emissions.
"With these findings, agricultural farming systems can be optimised with regard to their greenhouse gas emissions," Gattinger says. The results of the study will now have to be transferred to different soils, regions and cultivation systems through further long-term studies.
Skinner C, Gattinger A, Krauss M, Krause HM, Mayer J, van der Heijden MGA, Mäder P (2019) The impact of long-term organic farming on soil-derived greenhouse gas emissions. Scientific Reports, 9:1702; DOI: 10.1038/s41598-018-38207-w:
University Giessen, Institute for organic farming:
FiBL – Research Institute of Organic Farming