F A C U L T Y O F S C I E N C E U N I V E R S I T Y O F C O P E N H A G E N Conclusions • Drying periods have minimal impact on yields, while reducing overall GHG emission • Methane emission is strongly controlled by C availability in the substrate (on equal total C- input basis), increasing in the order: biochar-composts-animal manure-fresh material. • Direct comparison of treatments with and without biochar showed variable results, in some cases increasing CH4 emission, in other cases reducing it. • Cambodian farmers expressed concerns over labor consumption and re-supply of water after drainage. In response to that, we tested if early-season drainage could replace mid- season drainage, and demonstrated high potential • Nitrous oxide emissions generally increased with draining cycles, but did not lead to overall increase in GHG emissions as its contribution was balanced by lowered CH4 emissions. • In summary, drainage periods are even more important to mitigate emissions when including organic manures or residues in flooded rice, and early-season drainage should be further explored as a more safe and convenient option for smallholders. Andreas de Neergaard 1 , Proyuth Ly 1 , Quynh Duong Vu 2 , Arjun Pandey 1 , Azeem Tariq 1 , Syed Faiz-Ul Islam 1 and Lars Stoumann Jensen 1 1 Department of Plant and Environmental Sciences, University of Copenhagen, Denmark 2 Institute for Agricultural Environment, Vietnamese Academy of Agricultural Sciences , Hanoi , Vietnam Correspondance: [email protected] FACULTY OF SCIENCE UNIVERSITY OF COPENHAGEN Tweaking the system: optimization of mitigation strategies in smallholder flooded rice systems Ly et al. 2012. The system of rice intensification: Adopted practices, reported outcomes and their relevance in Cambodia. Agricultural Systems 113, 16-27 Ly et al. 2013. Methane (CH 4 ) and Nitrous Oxide (N 2 O) Emissions from the System of Rice Intensification (SRI) under a Rain-Fed Lowland Rice Ecosystem in Cambodia. 2013. Nutrient Cycling in Agroecosystems. 97, 13-27. Pandey et al. 2014. Organic matter and water management strategies to reduce methane and nitrous oxide emissions from rice fields in Vietnam. Agriculture, Ecosystems and Environment. 196, 137-146. Ly et al. 2015. Effects of rice straw, biochar and mineral fertiliser on methane (CH4) and nitrous oxide (N2O) emissions from rice (Oryza sativa) grown in a rain-fed lowland rice soil of Cambodia: a pot experiment. Paddy and Water Environment. DOI 10.1007/s10333-014-0464-9 Methane and nitrous oxide emissions from field trial in Vietnam, under two flooding systems and three organic amendments. AWD: Alternate wetting and drying; PF: Permanent flooding; FYM: Farmyard manure; SC: Straw compst; BC: Biochar. (Pandey et al 2014) • Methane emissions strongly affected by C additions in permanent flooding (PF), less so under alternate wetting and drying (AWD) • Nitrous oxide emissions less affected by water management than methane • Biochar marginally increases methane emission, no effect on nitrous oxide • Methane emissions strongly affected by C additions in permanent flooding (PF), less so under alternate wetting and drying (AWD) • Nitrous oxide emissions increased in fertilised treatments under AWD, but not enough to override methane mitigation • Overall GHG emission significantly lower under AWD Methane and nitrous oxide emissions from a pot trial, under two flooding systems and two organic amendments. AWD: Alternate wetting and drying; PF: Permanent flooding; DB: Deep bedding; MF: Mineral fertiliser Concerns about System of Rice Intensification expressed by Cambodian farmers, and reasons for non-adoption (Ly et al, 2012) • Both adopters and non- adopters express concerns about labour requirement, in spite of analysis showing equal or better return to labour input in SRI • Real concern is need of trusted family labour, as planting of young seedlings with even spacing requires more care Background Mid-season drainage in flooded rice is known to reduce CH 4 emission, while effects on N 2 O emissions are more variable. The use of complex organic fertilizers (manures, compost etc.) may result in highly variable greenhouse gas (GHG) emissions, depending on the N and C availability of the substrate and timing of flooding/drainage. In a series of field (Vietnam and Cambodia) and greenhouse experiments, we investigated the effect of a variety of organic amendments and wetting and drying cycles on yield and GHG emissions. Methane emissions from a pot trial, under two flooding systems and two organic amendments. AWD: Alternate wetting and drying; PF: Permanent flooding; DB: Deep bedding; MF: Mineral fertiliser • Early and mid-season drainage leads to significantly reduced methane emissions for weeks after re-flooding, presumably due to oxidation of amended C substrates Methane emissions from a pot trial with varying water management. T2: Mid season drainage. T6: Early and mid-season drainage. T7: Early and extended mid-season drainage • Reduced peak emission by early season drainage • Delayed emission by early season drainage • Continued emission supression after drainage T2 T6/T7