Journal
AGRICULTURE ECOSYSTEMS & ENVIRONMENT
Volume 239, Issue -, Pages 324-333Publisher
ELSEVIER
DOI: 10.1016/j.agee.2017.01.029
Keywords
Organic farming; Reduced tillage; Nitrous oxide; Soil organic carbon stocks; Grass-clover; Wheat
Funding
- COOP Sustainability fund
- CORE Organic II
- FP7 ERA-Net project
- Swiss Federal Office for the Environment (FOEN)
- Software AG-Stiftung
- Stiftung zur Pflege von Mensch, Mitwelt and Erde
- Swiss Federal Office for Agriculture (FOAG)
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Organic reduced tillage aims to combine the environmental benefits of organic farming and conservation tillage to increase sustainability and soil quality. In temperate climates, there is currently no knowledge about its impact on greenhouse gas emissions and only little information about soil organic carbon (SOC) stocks in these management systems. We therefore monitored nitrous oxide (N2O) and methane (CH4) fluxes besides SOC stocks for two years in a grass-clover ley - winter wheat - cover crop sequence. The monitoring was undertaken in an organically managed long-term tillage trial on a clay rich soil in Switzerland. Reduced tillage (RT) was compared with ploughing (conventional tillage, CT) in interaction with two fertilisation systems, cattle slurry alone (SL) versus cattle manure compost and slurry (MC). Median N2O and CH4 flux rates were 13 mu g N2O-N m(-2) h(-1) and -2 mu g CH4C m(-2) h(-1), respectively, with no treatment effects. N2O fluxes correlated positively with nitrate contents, soil temperature, water filled pore space and dissolved organic carbon and negatively with ammonium contents in soil. Pulse emissions after tillage operations and slurry application dominated cumulative gas emissions. N2O emissions after tillage operations correlated with SOC contents and collinearly to microbial biomass. There was no tillage system impact on cumulative N2O emissions in the grass-clover (0.8-0.9 kg N2O-N ha(-1), 369 days) and winter wheat (2.1-3.0 kg N2O-N ha(-1), 296 days) cropping seasons, with a tendency towards higher emissions in MC than SL in winter wheat. Including a tillage induced peak after wheat harvest, a full two year data set showed increased cumulative N2O emissions in RT than CT and in MC than SL. There was no clear treatment influence on cumulative CH4 uptake. Topsoil SOC accumulation (0-0.1 m) was still ongoing. SOC stocks were more stratified in RT than CT and in MC than SL. Total SOC stocks (0-0.5 m) were higher in RT than CT in SL and similar in MC. Maximum relative SOC stock difference accounted for +8.1 Mg C ha(-1) in RT-MC compared to CT-SL after 13 years which dominated over the relative increase in greenhouse gas emissions. Under these site conditions, organic reduced tillage and manure compost application seems to be a viable greenhouse gas mitigation strategy as long as SOC is sequestered. (C) 2017 The Authors. Published by Elsevier B.V.
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