Supervising Science Research Specialist 2017 Asia Sub-Group Meeting of the Paddy Rice Research Group And 5th Annual Meeting of MIRSA-2 Project Tsukuba International Congress Center (2-20-3 Takezono, Tsukuba, Ibaraki, 305-0032, Japan)  02 September 2017   SSPN Paper Summary: Philippines Evangeline B. Sibayan Supervising Science Research Specialist

Title: Effects of alternate wetting and drying technique on greenhouse gas emissions from irrigated rice paddy in Central Luzon, Philippines Authors: EB. Sibayana, KSPascuala, FS Grospea, MEDCasila, T Tokidac, AT Padreb, K Minamikawac Agencies : PhilRice, IRRI, NIAES-NARO

Corresponding author: Kristine S. Pascual, kcsamoy@gmail Corresponding author: Kristine S. Pascual, kcsamoy@gmail.com Type of contribution: Full-length paper Division: Environment Short running title: AWD feasibility in Philippines

Objectives of this study: to evaluate the feasibility of AWD in reducing CH4 emission during two distinct rice seasons, and to determine a suitable water management for reducing CH4 and N2O emissions and saving water without compromising grain yields from irrigated rice fields in Central Luzon, Philippines,

METHODOLOGY

Incorporated rice stubbles* Table S1. Field management practices during the six season field experiments in Central Luzon, Philippines. Season 2014DS 2014WS 2015DS 2015WS 2016DS 2016WS Plowing date 23-Dec-13 12-Jun-14 21-Dec-14 26-Jun-15 18-Oct-15 7-Jun-16 Variety NSIC Rc238 No. seedlings/hill 2-3 Transplanting date 13-Jan-14 27-Jun-14 12-Jan-15 10-Jul-15 15-Jan-16 29-Jun-16 Harvesting date 21-Apr-14 25-Sep-14 16-Apr-15 8-Oct-15 5-Apr-16 26-Sep-16 Date of Pesticide spraying 16-Jan-14 - 20-Jul-16 Pesticide/Herbicide Application Pesticide Herbicide Total N (kg N ha-1) 120 90 Total K (kg K2O ha-1) 40 total P (kg P2O5 ha-1) Straw management Incorporated rice stubbles* Incorporated rice stubbles

RESULTS

Figure 1. Methane, Nitrous Oxide Emissions and water level, temperature and rainfall during the 3 DS

Figure 2. Methane, Nitrous Oxide Emissions and water level, temperature and rainfall during the 3 WS

Methane Emission CH4 (g m-2) Cumulative emission

Nitrous oxide

Global Warming Potential - Season 5

Table 2. Seasonal CH4 and N2O emissions, GWP, rice grain yield, yield-scaled GWP, total water use, and water productivity as affected by cropping season and water management Treatment   CH4 (kg CH4 ha-1) N2O (kg N2O ha-1) GWP (kg CO2 eq ha-1) Grain yield (Mg ha-1) Yield-scaled GWP (Mg CO2 ha-1 Mg-1 grain) Water use (m-3 ha-1) Water productivity (kg m-3) DS WS CF 69.9 328.9 1.60 0.509 2853 11333 6.90 5.41 0.43 2.10 10336 10944 0.77 0.512 AWD 42.2 350.1 3.50 0.633 2476 12093 6.88 5.83 0.37 2.14 5913 9215 1.18 0.645 AWDS 52.8 374.0 2.63 0.528 2578 12874 5.42 0.41 2.46 5012 8949 1.43 0.615 Season mean 54.9 351.5 2.58 0.556 2636 12100 6.89 5.55 0.40 2.23 7087 9702 1.13 0.590 Treatment Means 199.4 A 1.05 B 7093 A 6.16 A 1.27 A 10640 A 0.642 B 196.1 B 2.07 A 7284 A 6.35 A 1.25 A 7564 B 0.914 A 213.4 A 1.58 B 7725 A 1.43 A 6980 B 1.023 A P value Source of variation df Cropping season (CS) 5 *** Dry or Wet (DW)1 1 Dry season (DS)1 2 0.502 ** † Wet season (WS)1 0.383 0.134 Main plot error 15 Treatment (T) * 0.776 0.666 0.496 T × CS 10 0.297 0.610 0.954 0.585 T × DW2 0.422 0.476 0.457 T × DS2 4 0.562 0.747 T × WS2 0.315 0.769 0.462 0.946 0.434 0.957 Split-plot error 36

SUMMARY OF FINDINGS

Lower seasonal CH4 emissions were obtained in DS than in WS. Higher CH4 reduction (60-51%) and GWP reduction (36-22%) relative to CF under AWD during season 5 (2016 DS), was achieved when dry plowing (5cm) was done a few days after harvest of previous crop and earlier drainage was imposed during the crop cycle Increased N20 fluxes were observed 1-5 days after N fertilizer application under AWD and AWDS during DS representing a significant portion of the total seasonal N2O emissions

Higher contribution of N2O emissions to the total GWP in DS. GWP reduction (at least 35%) was achieved only in 2016 DS by AWD relative to CF due to tillage after harvest of the previous crop and early start of AWD implementation at 10 DAT. Grain yields were not significantly different among treatments; DS yields were consistently higher than WS yields by 15 - 22%.

CONCLUSIONS Implementation of AWD is only feasible during DS in Central Luzon, Philippines 2. The AWD with the current settings significantly reduced the seasonal total CH4 emission, but the reduction rate against CF was very limited (1.7%). In addition, N2O emission was enhanced and the resultant GWP did not significantly differ among treatments.

LEARNINGS Feasible options that enhance the ability of AWD in reducing GHG emissions: an earlier rice residue incorporation under dry soil conditions, an earlier implementation of drainage, and a proper maintenance of flooded soil condition during/after N fertilizer topdressing.

RECOMMENDATION Further study is necessary to test the quantitative effect of these options under field conditions.

Acknowledgements To the Ministry of Agriculture Forestry and Fisheries (MAFF) of Japan through the International Research Project “Technology development for circulatory food production systems responsive to circulatory food production systems responsive to climate change: Development of mitigation options for greenhouse gas emissions from agricultural lands in Southeast Asia 2 (MIRSA 2) for the funding support, and To Prof. Kazuyuki Inubushi (Chiba University, Japan), Dr. Reiner Wassmann (IRRI, Philippines), and Dr. Kazuyuki Yagi (NIAES, Japan) for their valuable comments on the earlier version of this manuscript.

Thank you for your kind attention!