Water management and methane emission from rice cultivation: a case study in An Giang province, Viet Nam

Journal of Science and Technology 54 (2A) (2016) 91-97 WATER MANAGEMENT AND METHANE EMISSION FROM RICE CULTIVATION: A CASE STUDY IN AN GIANG PROVINCE, VIET NAM Duong Mai Linh 1 , Kenji Ishido 2 , Tomohiko Taminato 3 , Nguyen Huu Chiem 4 , Nguyen Xuan Loc 4, * 1 Faculty of Science - Technology - Environment, An Giang University, 18 Ung Van Khiem, Long Xuyen City, An Giang, Vietnam 2 Japan International Research Center for Agriculture Sciences, 1-1 Ohwashi, Tsukuba City, Ibaraki Prefecture, Japan; 3 Agriculture, Forestry and Fishery Department, Cabinet office Okinawa General Bureau, Japan 4 College of Environment and Natural Resources, Can Tho University, 3/2 Street, Ninh Kieu District, Can Tho City, Vietnam * Email: nxloc@ctu.edu.vn Received: 1 April 2016; Accepted for publication: 15 June 2016 ABSTRACT Rice cultivation causes the emission of CH4 consequenced to the global warming. Reduction of irrigation in rice cultivation is not only saving water resources but also reducing greenhouse gases emission. The objectives of this study was to determine impacts of water management on the emission of CH4 and rice yield. Experiment was conducted in field conditions in An Giang province, Viet Nam with three treatments as continuous flooding (CF), An Giang Alternative Wetting and Drying (AAWD) which is mostly applied by farmers in An Giang province-Viet Nam, and Alternate Wetting and Drying (AWD). Water levels in the field +5 cm, ± 5 cm and -15 cm were controlled higher, fluctuated and lower than soil surface, respectively for CF, AAWD and AWD. CH4 emission determined every week during 13 weeks of the experiment. Rice yield was determined in 1 m 2 at the end of the experiment. The results showed that AWD and AAWD, respectively decreased 78.7 % (p 0.05) CH4 emission compared to the CF 11.9 mg CH4/m 2 /h. The rice yield of CF was 6.32 ton/ha lower than AAWD 7.8 ton/ha (p < 0.05) but not different with AWD 6.67 ton/ha. AAWD had higher rice yield but same emission than the CF. Farmers in An Giang province should consider application of AWD in rice cultivation in term of saving water and reduction of CH4 emission. Key words: An Giang, AWD, CH4 emission, rice, water management. 1. INTRODUCTION Among sources of CH4 emission, agricultural production accounts for 50.6 % of annual greenhouse gases (GHGs) mission [1], in which wet rice cultivation accounts for a large amount. Duong Mai Linh, Kenji Ishido, Tomohiko Taminato, Nguyen Huu Chiem, Nguyen Xuan Loc 92 Vietnam is one of the most countries emitting CH4 [2]. Rice production activities produce 37,429 thousand tons of CH4, contributing 58% of total GHGs emission [3]. Main source of emission in wet rice cultivation is overuse of chemical fertilizers, resulting an increase fertilizer loss and causing soil pollution and N2O emission [4]. Besides, stagnant water in rice field consequence to CH4 and CO2 emission. Therefore, reducing GHGs emission in agriculture production attracts attentions of public over the world and in Vietnam. This study was conducted to test whether water management in the paddy field affects CH4 emission and the rice yield of farmers in Chau Thanh village, An Giang province. 2. METHODOLOGY 2.1. Experimental site The study was conducted on rice fields in Binh Hoa village, Chau Thanh district, An Giang province in Winter-Spring season 2015. The treatments were arranged in a randomly completed design with 3 treatments and 3 replicates (plots) for each treatment. The rice variety Jasmine 85 was used in the experiment. 2.2. Experimental set-up Treatment 1 (CF - continuous flooding): the water level was maintained at + 5cm above the soil surface. Treatment 2 (AAWD – An Giang alternative wetting and drying): current cultivation of farmers in Binh Hoa village followed the handbook of the Department of Agriculture & Rural Development, An Giang province [5]. The water level was controlled -5 cm to +5 cm compared to soil surface. Treatment 3 (AWD - alternative wetting and drying): irrigation followed alternative wetting and drying. The water level was controlled at -15 cm below the soil surface. Figure 1. The locations and experimental design. N Water management and methane emission from rice cultivation: a case study 93 The Figure 1 showed the locations and experimental design. The water levels in each plot were recorded every day during the experiment by water gauges. Soil reduced and oxidized potential (Eh) and gas samples collected in closed chambers were sampled weekly. The gas samples in each chamber were collected at 3 rd and 23 th minute after setting the chamber on the field. CH4 was analysed with FID detector, Shimadzu. The CH4 emission is estimated by the following Taminato equation [6]: 4 273 3600 22,4 100 273 C CH M V m S T where: mCH4: emission flux of CH4 (mg CH4/m 2 /h); Mc: molecular weight of carbon (12 g/mol); V: volume of chamber (cm 3 ); S: chamber area (cm 2 ); T: absolute temperature calculated as 273 + temperature ( o C) in the chamber. 2.3. Statistics analysis The software SPSS 21.0 (IBM Inc., USA) was used to analyse one-way ANOVA for CH4 emission and rice yields among treatments and correlation between CH4 emission and rice growth stage. The data was tested homogeneity and transformed (if necessary) before analysing. 3. RESULTS AND DISCUSSIONS 3.1. Water management in the experimental fields Figure 2. The mean of water level in experimental models in Winter-Spring season. CF: continuous flooding; AAWD: An Giang alternative wetting and drying; AWD: alternative wetting and drying. Figure 2 showed that water level fluctuation of the 3 treatments. At the beginning of the crop (5 days after sowing), the rice needed water to germinate and elongate roots. During 60 th to 75 th day after sowing, the rice also needed water to produce flowers and seeds. And, at the end of the crop (5 days before harvesting), the water was withdrawn for rice ripening and harvesting [5]. Duong Mai Linh, Kenji Ishido, Tomohiko Taminato, Nguyen Huu Chiem, Nguyen Xuan Loc 94 3.2. CH4 emission CH4 emission was different among the treatments (Fig. 3). The variation of CH4 emission of the 3 treatments had the same patterns through rice growth stages. At 5 days after sowing, CH4 emission was 0.24 mgCH4/m 2 /h in CF treatment, 0.74 mgCH4/m 2 /h in AAWD treatment and 0.40 mgCH4/m 2 /h in AWD treatment. Then, the emission increased continuously and respectively reached peaks of 28.52 mgCH4/m 2 /h in CF, 35.80 mgCH4/m 2 /h in AAWD and 9.92 mgCH4/m 2 /h in AWD in the tillering stage. The CH4 emission decreased gradually, then increased slightly in the week 11 th in the flowering stage which were 12.81 mgCH4/m 2 /h, 8.82 mgCH4/m 2 /h and 2.45 mgCH4/m 2 /h in CF, AAWD and AWD, respectively. After the 7 weeks, CH4 emission continued to decline until the end of crop. Figure 3. CH4 emission in Winter-Spring season. CF: continuous flooding; AAWD: An Giang alternative wetting and drying; AWD: alternative wetting and drying. CH4 emission fluctuated through the growth stages of rice and had 3 peaks at week 3 rd after sowing, tillering stage and flowering stage (week 6 th ) [7]; and reduced the emission at the end of tillering stages and the maturity stage (week 11 th ). This result was consistent with studies of Baharati [8]. The CH4 emission were also reported highest 30-40 mg/m 2 /h [9, 10]. Table 1. CH4 emission. Treatment Average Compared to control mgCH4/m 2 /h Kg CH4/ha/season CF 11,93 ± 7,17 b 257,69 - AAWD 11,12 ± 9,81 b 240,19 -6,79% AWD 2,54 ± 3,52 a 54,86 -78,7% CF: continuous flooding; AAWD: An Giang alternative wetting and drying; AWD: alternative wetting and drying; mean± std, At the beginning of the crop (5 days after sowing), the CH4 emission increased gradually and there were no significant differences among treatments (p<0.05). In this stage, all plots were stagnant to keep soil anaerobic and limit grass germination. In the tillering stage (30-40 days after sowing), CH4 emission was the highest in the 3 treatments. In this stage, the rice was Water management and methane emission from rice cultivation: a case study 95 tillering and had root elongation to deep soil; hence, CH4 emitted quickly to the air. During the day 41 th to 61 th , water was withdrawn from the field because the rice needed less water. In this stage, the CH4 emission also decreased gradually since soil became dry. In the flowering stage (61-75 days after sowing), CH4 emission increased insignificantly slightly through the root systems and stems [11]. After the flowering stage, CH4 emission decreased until the end of crop because the water level in the field was low for rice ripening and for introduction of machine to the field for easily harvest. The CH4 emission for the whole crop showed that AWD reduced the emission compared to CF and AAWD. Application of AWD on rice cultivation could reduce nearly 80% CH4 emission compared to CF (Table 1). 3.3. Rice yield Table 2. Rice yield. Treatment Yield (ton/ha) CF 6.32 ± 0,06 a AAWD 7.80 ± 0,93 b AWD 6.67 ± 0,68 ab CF: continuous flooding; AAWD: An Giang alternative wetting and drying; AWD: alternative wetting and drying; mean± std, Table 2 showed that AAWD treatment had the yield 7.80 ton/ha higher than CF 6.67 ton/ha (p 0.05) with AWD treatment 6.36 ton/ha. Therefore, AWD application should be considered to apply in An Giang province. 3.4. The correlation between CH4 emission and rice growth stage Figure 4. The correlation between CH4 emission and rice growth stage. CF: continuous flooding; AAWD: An Giang alternative wetting and drying; AWD: alternative wetting and drying Duong Mai Linh, Kenji Ishido, Tomohiko Taminato, Nguyen Huu Chiem, Nguyen Xuan Loc 96 Correlation of CH4 emission in three treatments (reference data from Summer-Autumn crop 2014 and Autumn-Winter crop 2014) had an upward trend from the sowing stage, had a peak in the tillering stage, then decreased to the end of the crop (Fig. 4). CH4 emission in rice fields was depend mainly on the growth stages of the rice. The CH4 emission the paddy field may be reduced in terms of water management. This result was agree with the previous study of Yingming [7, 9]. Additional discussions are needed, especially by considering this finding with others in Vietnam or in the worlds. 4. 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