Dear Friends and Colleagues
Organic Cropland Emits 40% Less Greenhouse Gas Than Conventional Cropland
With a share of 10–12% in carbon-dioxide equivalents (CO2-eq.), agriculture contributes substantially to global greenhouse gas (GHG) emissions. Considering indirect emissions from agriculture-related activities such as fertiliser production and land use change, this share can be up to 30%. In 2005, the agricultural sector contributed 56% to the emissions of the anthropogenic non-CO2 GHGs, i.e. nitrous oxide (N2O) and methane (CH4). An estimated 38% of agriculture’s direct emissions originate from soils, 15% from N2O from manure on pasture and 12% from N2O of synthetic fertilisers. Due to their high global warming potential (GWP), the reduction of N2O and CH4 emissions thus gives agriculture’s mitigation potential a high leverage in favour of limiting global warming.
A long-term field trial has compared the bio-dynamic (D), bio-organic (O) and conventional (K) cultivation of arable crops such as wheat, potatoes, maize soy or clover grass at the same site in Switzerland since 1978. By measuring soil gas fluxes in the farming systems of the DOK trial, researchers examined the impact of organic farming on direct GHG emissions. Two organic farming systems; bioorganic (with slurry and rotted manure) and biodynamic (with slurry and composted manure), and two non-organic; conventional with livestock (with slurry, fresh stacked manure and synthetic fertilisers) and without (only synthetic fertilisers), all fertilised to an intensity typically practiced in Switzerland, were chosen for the experiment. An unfertilized/zero fertilisation control was included.
The result was that the organically farmed areas had around 40% lower nitrous oxide emissions per hectare than the conventionally (non-organic) farmed plots. Diversified crop sequencing was a precondition. The study also found that, in addition to nitrogen input, quality properties such as pH, soil organic carbon and microbial biomass significantly affected N2O emissions.
The study shows that it is not only the renunciation of larger amounts of chemical fertilisers that leads to reduced emissions, but also the targeted use of diverse crop rotations and farm-based amendments such as farmyard manure and slurry to maintain important soil functions. Adapted fertilisation strategies in organically managed soils therefore can prevent excessive N2O emissions despite higher N2O emission potential. Organic farming systems can thus be a viable measure contributing to greenhouse gas mitigation in the agricultural sector.
With best wishes
THE IMPACT OF LONG-TERM ORGANIC FARMING ON SOIL-DERIVED GREENHOUSE GAS EMISSIONS
C, Gattinger A, Krauss M, Krause HM, Mayer J, van der Heijden MGA,
Agricultural practices contribute considerably to emissions of greenhouse gases. So far, knowledge on the impact of organic compared to non-organic farming on soil-derived nitrous oxide (N2O) and methane (CH4) emissions is limited. We investigated N2O and CH4 fluxes with manual chambers during 571 days in a grass-clover– silage maize – green manure cropping sequence in the long-term field trial “DOK” in Switzerland. We compared two organic farming systems – biodynamic (BIODYN) and bioorganic (BIOORG) – with two non-organic systems – solely mineral fertilisation (CONMIN) and mixed farming including farmyard manure (CONFYM) – all reflecting Swiss farming practices–together with an unfertilised control (NOFERT). We observed a 40.2% reduction of N2O emissions per hectare for organic compared to non-organic systems. In contrast to current knowledge, yield-scaled cumulated N2O emissions under silage maize were similar between organic and non-organic systems. Cumulated on area scale we recorded under silage maize a modest CH4 uptake for BIODYN and CONMIN and high CH4 emissions for CONFYM. We found that, in addition to N input, quality properties such as pH, soil organic carbon and microbial biomass significantly affected N2O emissions. This study showed that organic farming systems can be a viable measure contributing to greenhouse gas mitigation in the agricultural sector.
Cropland farmed organically over a longer period emits 40 per cent less greenhouse gases per hectare than conventionally farmed cropland. This has been revealed in results from a world-wide unique long-term field trial. Diversified crop sequencing is a precondition.
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.
Bio-dynamic with the lowest laughing gas values
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.