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 Neergaard1, Proyuth Ly1, Quynh Duong Vu2, Arjun Pandey1, Azeem Tariq1, Syed Faiz-Ul Islam1 and Lars Stoumann Jensen1 1 Department of Plant and Environmental Sciences, University of Copenhagen, Denmark 2 Institute for Agricultural Environment, Vietnamese Academy of Agricultural Sciences , Hanoi , Vietnam

Correspondance: adn@plen.ku.dk

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 (CH4) and Nitrous Oxide (N2O) 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 CH4 emission, while effects on N2O 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