Site-specific feasibility of alternate wetting and drying as a greenhouse gas mitigation option for irrigated rice systems in Asia Greenhouse gas Mitigation in Irrigated Rice Systems in Southeast Asia (Part 2) Agnes Padre1, Prihasto Setyanto2, Ali Promono2, Tran Dang Hoa3, Hoang Trong Nghia3, Amnat Chidthaisong4, Chitnucha Buddhaboon5, Nittaya Chaun4, Benjamas Rossopa5, Evangeline Sibayan6, Kristine Pascual6, Kazunori Minamikawa7, Yusuke Takata7, Kazuyuki Yagi7, and Reiner Wassmann1 1International

Rice Research Institute, Los Baños, Laguna, Philippines, 2 Indonesian Agricultural Environment Research Institute, Jakenan, Pati Central Java, Indonesia, 3 Hue University of Agriculture and Forestry, Hue City, Vietnam 4The Joint Graduate School of Energy and Environment, King Mongkut's University of Technology Thonburi, Bangkok, Thailand 5Prachinburi Rice Research Center, Bansang, Prachinburi, Thailand 6PhilRice Central Experiment Station, Muñoz, Nueva Ecija, Philippines 7National Institute for Agro-Environmental Sciences, Tsukuba, Ibaraki, Japan

Introduction Simultaneous experimental field trials were initiated in Sept 2013 in Jakenan Central Java Indonesia, Muñoz Nueva Ecija Philippines, Bansang Prachinburi Thailand, and Hue Vietnam, to assess the site-specific feasibility of alternate wetting and drying (AWD) as a mitigation option for CH4+N2O emissions from irrigated rice fields. The study aims to develop guidelines on the effective implementation of AWD at multiple locations in Southeast Asia to achieve the emission reduction target of 30% relative to the conventional water management, and to acquire a generalized scientific knowledge about the influence of AWD on GHG emission reduction. Here results from the first two seasons (1 year) are presented. The field trials will continue for 3 years (6 cropping seasons).

Site Characteristics Site

Hue

Prachinburi

Jakenan

Muñoz

Soil Texture % clay % sand % silt pH % Total organic C % Total N Rice Variety Crop establishment N:P2O5:K2O kg ha-1

loam 17.8 49.3 32.4 4.18 1.25 0.068 HT1 Wet seeding

Clay 62.9 10.4 26.7 4.9 1.93 0.18 RD41 Wet seeding

101:72:62

70:37.5:37.5

120:60:60

120:40:40

Organic fertilizer kg ha-1

1000 (microbial fertilizer)

0

5000 (farmyard manure)

0

Silt loam Clay 19.54 44 31.37 17 49.09 39 6.46 6.44 0.44 1.23 0.15 0.10 Cisadane NSIC Rc238 Dry seeding (WS) Transplanting Transplanting (DS)

mm Rain

Cropping and Rainfall Patterns

Methodology Experimental design: Randomized complete block Treatments: 1) Continuously flooded, 2) Safe AWD (irrigate when water level reaches -15 cm),

Minamikawa, K., Tokida, T., Sudo, S., Padre, A., Yagi, K. (2015) Guidelines for measuring CH4 and N2O emissions from rice paddies by a manually operated closed chamber method. National Institute for Agro-Environmental Sciences, Ts u ku b a , J a p a n . D o w n l o a d at http://www.niaes.affrc.go.jp/index_e.html

and 3) site specific AWD

Gas sampling and analysis:

By manual chambers and gas chromatography Sampling time: 9-11 AM Sampling frequency: once a week and everyday for 5 days after N fertilizer application Chamber deployment time: 30 mins Sampling intervals: 0, 6, 12, 20, 30 mins Gas sample storage: evacuated glass vials Flux estimation: linear regression Seasonal emissions: sum of daily emission rates. Daily emissions in between weekly measurements were estimated from a linear interpolation of two consecutive weekly measurements GWP calculation: estimated from CH4 and N2O emissions using the factors (relative to CO2 over a 100-yr time horizon) of 25 and 298, respectively.

These guidelines were commissioned by the Secretariat of the Agriculture, Forestry and Fisheries Research Council of the Ministry of Agriculture, Forestry and Fisheries of Japan through the MIRSA-2 project to support the goals and objectives of the Paddy Rice Research Group of the Global Research Alliance on Agricultural Greenhouse Gases (PRRG-GRA).

Results and Conclusions Hue Vietnam SITE Minimum water level No. of days without surface water CH4 kg ha-1 season-1 N2O kg ha-1 season-1 GWP Mg CO2 eq. ha-1 % GWP reduction through AWD

Season 1 CF AWD AWDS

512 0.29 12.9

-20 17

-15 28

396 0.36 10.0 22

429 0.30 10.8 16

CF

1029 1.05 26.0

Prachinburi Thailand

Season 2 AWD AWDS -13 26

-9 11

814 0.71 20.5 21

810 0.57 20.3 22

Season 1 AWD AWDS

CF

24.7 1.64 1.10

-15 20

-15 8

12.3 3.29 1.30 -17

23.9 2.69 1.40 -26

CF

13.0 5.43 1.94

 The 4 MIRSA sites vary in their soil properties, water regime, cropping and rainfall patterns, and farm management that contribute to the variabilities in CH4 and N2O emissions. Hue and Prachinburi soils are classified as wet, having a more redox condition than Jakenan and Muñoz soils which are dry. However, Prachinburi soils have many mottles in the sub-surface horizons enabling seasonal oxidation in the soil pores. High CH4 and low N2O emissions were measured in Hue while low CH4 and high N2O emissions were measured in Prachinburi.  Muñoz soil, also classified as “Ustic”, may be in a more oxidized condition than Jakenan soil. CH4 emissions in Muñoz were very low during the dry season but were high in Jakenan (next to Hue) probably due to the addition of farmyard manure.  The AWD treatments varied across sites and seasons based on the minimum water level and number of days without surface water. Safe AWD (-15 cm water level) could not always be achieved due to continuous rain during the wet season, and low soil infiltration rate in the clayey soils.

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PRRC

Jakenan Indonesia

Season 2 AWD AWDS -4 3

-6 5

3.4 4.47 1.42 27

5.8 4.61 1.52 21

Season 1 CF AWD AWDS

250 0.99 6.54

-46 17

-64 14

160 1.01 4.31 34

158 0.68 4.16 36

CF

300 1.48 7.94

Muñoz Philippines

Season 2 AWD AWDS -15 27

-26 10

168 1.24 4.57 42

253 1.39 6.74 15

Season 1 CF AWD AWDS

32.2 1.97 1.39

-15 18

-7 11

5.7 3.92 1.31 6

25.5 1.05 0.95 31

CF

Season 2 AWD AWDS -6 4

438 581 0.37 0.54 11.06 14.68 -33

-9 8 533 0.47 13.46 -22

 The daily average CH4 emissions were significantly reduced under AWD in all the sites in both seasons except for Muñoz in season 2 (wet season) when the minimum water level reached only -6 to -9 cm with only 4 – 8 days without soil surface water, due to continuous rain during the early stages of the rice crop.  N2O emissions increased under AWD relative to that under CF during the dry season in Prachinburi and Muñoz which offset the CH4 emission reduction in Prachinburi but not in Muñoz.  Grain yields were not significantly different among the CF and AWD treatments in both seasons in all sites.  The 30% emission reduction target for AWD was achieved only in Jakenan during the first 2 seasons. Thus, a more drastic AWD (lower than -15 cm water level or increased no. of days without surface water) are being considered in succeeding seasons to attain the emission reduction target without any yield penalty.

KMUTT/JGSEE HUAF