SoilUse and Management doi: 10.1111/sum.12229
Soil Use and Management
Suppressing methane emission and global warming potential from rice fields through intermittent drainage and green biomass amendment M D . M. H A Q U E 1 , 2 , J. C. B I S W A S 2 , S. Y. K I M 3 & P. J. K I M 1 , 4 1
Division of Applied Life Science (BK 21 Program), Gyeongsang National University, Jinju 660-701, South Korea, 2Soil Science Division, Bangladesh Rice Research Institute, Gazipur 1701, Bangladesh, 3Department of Microbial Ecology, Netherland Institute of Ecology (NIOO-KNAW), Wageningen, the Netherlands, and 4Institute of Agriculture and Life Sciences, Gyeongsang National University, Jinju 660-701, South Korea
Abstract Winter cover crops are recommended to improve soil quality and carbon sequestration, although their use as green manure can significantly increase methane (CH4) emission from paddy soils. Soil management practices can be used to reduce CH4 emission from paddy soils, but intermittent drainage is regarded as a key practice to reduce CH4 emission and global warming potential (GWP). However, significantly greater emissions of carbon dioxide (CO2) and nitrous oxide (N2O) are expected when large amounts of cover crop biomass are incorporated into soils. In this study, we investigated the effects of midseason drainage on CH4 emission and GWP following incorporation of 0, 3, 6 and 12 Mg/ha of cover crop biomass. Methane, CO2 and N2O emission rates significantly (P < 0.05) increased with higher rates of cover crop biomass incorporation under both irrigation conditions. However, intermittent drainage effectively reduced seasonal CH4 fluxes by ca. 42–46% and GWP by 17–31% compared to continuous flooding. Moreover, there were no significant differences in rice yield between the two water management practices with similar biomass incorporation rates. In conclusion, intermittent drainage and incorporation of 3 Mg/ha of green biomass could be a good management option to reduce GWP.
Keywords: Greenhouse gas emission, global warming potential, water management, organic amendment
Introduction Rice feeds about a third of the world’s population, and its cultivation has increased from 104 to 148 million ha over the last half century (Aulakh et al., 2001; Conrad, 2007). Asian countries such as China, India, Indonesia and Bangladesh represent about 90% of the global area under rice cultivation (FAO, 2012). Poor soil organic matter content and imbalanced nutrient management are main factors that can explain reduction in grain yields in several areas where rice is grown (Nambiar, 1995; Reddy & Krishnaiah, 1999). To maintain desired agricultural productivity and sustainability, application of organic materials has been
Correspondence: Md. M. Haque and P. J. Kim. E-mail: mhaquesoil @yahoo.com and
[email protected] Received February 2015; accepted after revision September 2015
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recommended as a major remedial measure to increase soil organic matter in these cases. Recycling of crop residues can improve overall soil conditions and support sustainable crop productivity (Smith, 1992). However, increasing demand by Korea’s livestock industry for rice straw as feedstuff has resulted in a marked decrease of its use in rice fields from ca. 3.7 Mg/ha in 1992 to ca. 1.1 Mg/ha in 1998 (Kim et al., 2003). In recent years, winter cover crop cultivation as green manure during the fallow season has been recommended as an alternative practice. Wetland rice has been identified as an important source of greenhouse gases (GHG) such as methane (CH4), carbon dioxide (CO2) and nitrous oxide (N2O) (Harris et al., 1985; Bouwman, 1990; Solomon et al., 2007; Lee, 2010), which account for 26–60–14%, respectively, of global warming (Rodhe, 1990; Neue & Roger, 1993; IPCC 2007). Greenhouse gas emission mainly takes place from decomposing organic materials, microbial decay and
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2 Md. M. Haque et al. microbial transformation of nitrogen in soils and manures under reduced conditions (Takai, 1961; Garcia et al., 2000; Janzen, 2004; Oenema et al., 2005). Moreover, addition of organic materials such as green manure can promote GHG emission by providing readily available carbon and nitrogen to microorganisms (Neue et al., 1997; Hadi et al., 2010; Lee, 2010; Haque et al., 2013; Kim et al., 2013). It is likely that improved crop production strategies conflict with mitigation of GHG emission (Hsu et al., 2009) from rice fields, although several options to reduce CH4 emissions such as midseason or intermittent drainage are expected to decrease CH4 emissions by changing soil redox conditions (Yagi et al., 1996). A number of reports showed reduction in CH4 emissions from paddy fields due to mid season drainage (Minamikawa & Sakai, 2006; Shiratori et al., 2007) but CO2 and N2O emissions rates increased (Miyata et al., 2000; Saito et al., 2005). However, no or inadequate data are available in relation to cover crop biomass incorporation rates and GHG emission. Therefore, it is necessary to find out the optimum rate of green biomass incorporation with altered water management to minimize GHG emission and GWP from paddy fields.
Materials and methods Experimental field preparation and rice cultivation The field experiment was carried out from June to October, 2013, in the Gyeongsang National University (36°500 N and 128°260 E), Jinju, South Korea. The soil was a silt loam with 20.4 3.9 g/kg of organic matter, 0.70 g/kg of total nitrogen, a pH (1:5 with H2O) of 6.2 0.32 and extractable P2O5 of 78.7 3.1 mg/kg (Lancaster method). In Korea, the recommended rate of seed application for barley and hairy vetch as winter cover crop is 180 and 90 kg/ha, respectively (Jeon et al., 2011; Haque et al., 2013), but a mixture of seeds of barley (75% of the recommended dose, RD) and vetch (25% of RD) has been broadly utilized in Korean agricultural lands to improve biomass productivity and soil fertility (Haque et al., 2013; Haque et al., 2015b). This mixture of barley and vetch seeds was broadcasted after rice harvest in 2012. On the 1st of June 2013, the aboveground biomass of the cover crop was harvested manually at mid-maturing stage of barley (204 days after seeding). Total aboveground fresh biomass was recorded. The biomass was manually chopped (size 5–10 cm) and applied at rates of 0, 3, 6 and 12 Mg/ha on an air-dried weight basis. The green manure was mixed mechanically with surface soil one week before flooding and rice transplant. Each treated plot (10 m 9 10 m) was arranged with three replications following a randomized block design. Two water management treatments, continuous flooding and intermittent drainage, were maintained during the growing season. In the intermittent drainage treatment,
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flooding was ceased for 30 days three weeks after transplant (20–50 DAT) and then flooding was restored up to harvest. Continuous flooding treatment was under flooding conditions during the whole cultivation period. Twenty-one-day-old seedlings (4 rice seedlings per hill) of rice cultivar (Dongjinbyeo, Japonica type) were transplanted at 15 9 30 cm spacing on 8th June 2013. Recommended dose of NPK fertilizers (90–20–48 kg/ha) was applied one day before rice transplant (RDA, 1999). The soil was flooded one week before transplant, and the water level maintained at 5–7 cm depth.
CH4, N2O and CO2 gas sampling and analyses A closed-chamber method was used to estimate CH4, N2O and CO2 emissions during rice cultivation (Rolston, 1986; Ali et al., 2009; Haque et al., 2013, 2015a,b). Transparent glass chambers with a surface area of 62 9 62 cm and a height of 112 cm were placed permanently on the flooded soil after rice transplant to monitor CH4 and N2O emission rates. Eight rice plants were covered by each chamber. There were four holes at the bottom of the chamber to maintain the water level. For CO2 gas sampling, a separate acrylic column chamber (diameter of 20 cm and height of 20 cm) was placed near the transparent glass chambers between rice plants on flooded soil having holes at the bottom to control water movement (Lou et al., 2004; Xiao et al., 2005; Iqbal et al., 2008). All chambers were kept open in the field except during gas sampling. The chamber was equipped with a circulating fan to mix the gas and a thermometer inside to monitor temperature during sampling time. Air sampling from the glass chambers was carried out using 50-mL airtight syringes at 0 and 30 min after closing the top of the chamber. Gas samplings were carried out at 8 am, 12 pm and 4 pm to get average CH4, N2O and CO2 emission rates. Gas samples from each treatment were drawn off in triplicate, and collected samples were immediately transferred into 30-mL air-evacuated glass vials sealed with a butyl rubber septum for analysis. Methane, N2O and CO2 concentrations in the collected air samples were measured by gas chromatography (GC-2010; Shimadzu, Japan) packed with a Porapak NQ column (Q 80–100 mesh) and equipped with a flame ionization detector and a thermal conductivity detector. Temperatures for the column, injector and detector were adjusted at 100, 200 and 200°C and 45, 75 and 270°C for CH4, N2O and CO2 analysis, respectively. Helium and H2 were used as carrier and combustion gases for CH4, N2O and CO2 analysis, respectively.
Estimation of CH4, CO2 and N2O emissions Methane, CO2 and N2O emission rates were calculated from the increase in CH4, CO2 and N2O concentrations per unit
Intermittent drainage suppressing methane emission and global warming potential from rice fields
surface area of the chamber for a specific time interval. A closed-chamber equation (Rolston, 1986; Lou et al., 2004) was used to estimate CH4, CO2 and N2O fluxes from each treatment. F ¼ q ðV=AÞ ðDc=DtÞ ð273=TÞ where F is CH4 and CO2 (mg/m2/h), and N2O fluxes (lg N2O/m2/h), q is the gas density of CH4, CO2, and N2O under a standardized state (mg/cm3), V is the volume of the chamber (m3), A is the surface area of the chamber (m2), Dc/ Dt is the rate of increase of CH4, CO2, and N2O gas concentrations in the chamber (mg/m3/h), and T is absolute temperature inside the chamber. Seasonal CH4, CO2 or N2O fluxes for the entire crop period were computed as reported by Singh et al. (1999): Seasonal CH4 ; CO2 or N2 O fluxes ¼
X
in ðRi Di Þ
where Ri is the rate of CH4, CO2 or N2O fluxes (g/m2/day) in the i th sampling interval, Di is the number of days in the i th sampling interval, and n is the number of sampling intervals.
Global warming potential The global warming potential (GWP) was determined in terms of CO2 equivalent (Robertson et al., 2000; IPCC 2007): GWP ðCO2 equivalentÞ ¼ 1 CO2 þ 25 CH4 þ 298 N2 O
Rice plant growth and yield characteristics Rice plant growth parameters such as plant height and tiller numbers were measured at harvest. Yield components such as number of grains per panicle, ripened grains, 1000 grain weight and grain yield were determined at harvest.
Soil properties The redox potential of the paddy soil was measured weekly by a Eh meter (PRN-41, DKK-TOA Corporation) during rice cultivation. The electrode was permanently installed in the soil at a 5 cm depth. Soil samples were collected at rice harvest from the surface layer (0–15 cm depth), air-dried and sieved through
