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| Titel |
Soil organic carbon dynamics and non-CO2 gas fluxes from agricultural soils under organic and non-organic management - results of two meta-studies |
| VerfasserIn |
Andreas Gattinger, Colin Skinner, Adrian Müller, Paul Mäder, Urs Niggli |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250108572
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| Publikation (Nr.) |
 EGU/EGU2015-8334.pdf |
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| Zusammenfassung |
| It is anticipated that organic farming systems provide benefits concerning soil conservation
and climate protection. Therefore, meta-studies on soil organic carbon (SOC) and
soil-derived greenhouse (GHG) fluxes, respectively, were conducted to proof this assumption.
Datasets from 74 studies from pair wise comparisons of organic versus non-organic
farming systems were subjected to meta-analysis to identify differences in soil organic
carbon (SOC). We found significant differences and higher values for organically
farmed soils of 0.18±0.06 % points (mean±95% confidence interval) for SOC
concentrations, 3.50±1.08 Mg C ha-1 for stocks, and 0.45±0.21 Mg C ha-1 a-1
for sequestration rates compared to non-organic management. Meta-regression
did not deliver clear results on drivers, but differences in external C inputs and
crop rotations seemed important. Restricting the analysis to zero net input organic
systems, i.e.Âwithout nutrient inputs from outside the system, and retaining only the
datasets with highest data quality (measured soil bulk densities and external C and N
inputs), the mean difference in SOC stocks between the farming systems was still
significant (1.98±1.50 Mg C ha-1), while the difference in sequestration rates became
insignificant (0.07±0.08 Mg C ha-1 a-1). The SOC dataset mainly covers top soil and
temperate zones, while only few data from tropical regions and sub soil horizons
exist.
For the second meta-study measured soil-derived nitrous oxide and methane flux data from
soils under organic and non-organic management from 19 farming system comparisons were
analysed. Based on 12 studies that cover annual measurements, it appeared with a high
significance that area-scaled nitrous oxide emissions from organically managed soils are
492±160 kg CO2 eq. ha-1 a-1 lower than from non-organically managed soils. For arable
soils the difference amounts to 497±162 kg CO2 eq. ha-1 a-1. However, yield-scaled nitrous
oxide emissions are higher by 41±34 kg CO2 eq. t-1 DM under organic management
(arable and use). To equalize this mean difference in yield-scaled nitrous oxide
emissions between both farming systems, the yield gap has to be less than 17%.
Emissions from conventionally managed soils seemed to be influenced mainly by
total N inputs, whereas for organically managed soils other variables such as soil
characteristics seemed to be more important. This can be explained by the higher
bioavailability of the synthetic N fertilisers in non-organic farming systems while
the necessary mineralisation of the N sources under organic management leads to
lower and retarded availability. Furthermore, a higher methane uptake of 3.2±2.5 kg
CO2 eq. ha-1 a-1 for arable soils under organic management can be observed.
Only one comparative study on rice paddies has been published up to date. All
19 retrieved studies were conducted in the Northern hemisphere under temperate
climate.
Summarizing, the two meta-studies show that organic farming has the potential
to accumulate soil carbon and to reduce soil-derived nitrous oxide and methane
fluxes. |
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