Water Air Soil Pollut (2014) 225:2118 DOI 10.1007/s11270-014-2118-3
Mitigation of Greenhouse Gas Emissions by Water Management in a Forage Rice Paddy Field Supplemented with Dry-Thermophilic Anaerobic Digestion Residue S. Riya & M. Katayama & E. Takahashi & S. Zhou & A. Terada & M. Hosomi
Received: 15 April 2014 / Accepted: 7 August 2014 / Published online: 22 August 2014 # Springer International Publishing Switzerland 2014
Abstract Dry-thermophilic anaerobic co-digestion (DTAD) can be used to treat forage rice straw and pig manure and generate biogas as an energy source. Solid residue produced from DTAD process can be used as a fertilizer in forage rice fields, while addition of the residue could increase methane (CH4) and nitrous oxide (N2O) emissions from the soil. We evaluated the effects of adding DTAD residue and water management on CH4 and N2O emissions from a forage rice field. Three treatments were evaluated: (a) 100 kg N·ha−1 chemical fertilizer and continuous flooding (CC); (b) residue addition (300 kg N·ha−1 DTAD residue) with continuous flooding (RC); and (c) residue addition with intermittent irrigation (RI). RC and RI showed higher CH4 fluxes than CC throughout the growing period. After a midsummer drainage, RI showed higher soil Eh values and lower CH4 fluxes (mean, 7.6 mg C·m−2 ·h−1) than those in RC (mean, 18.6 mg C·m−2 ·h−1). Abundance of mcrA gene copy number was not different between RC and RI, suggesting CH4 flux was reduced by suppression of methanogenic activity by intermittent irrigation. S. Riya (*) : M. Katayama : E. Takahashi : A. Terada : M. Hosomi Department of Chemical Engineering, Faculty of Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei, Tokyo 184-8588, Japan e-mail:
[email protected] S. Zhou Eco-environmental Protection Research Institute, Shanghai Academy of Agricultural Sciences, 1000 Jinqi Road, Fengxian, Shanghai 201403, China
Cumulative CH4 emissions during the cultivation period were 105, 509, and 306 kg C·ha−1 in CC, RC, and RI, respectively. N2O fluxes were within detection limits in all treatments. Our results, to our knowledge, are the first to show greenhouse gas emission from forage rice fields supplemented with DTAD residue and of the effectiveness of water management in CH4 mitigation. Keywords Methane . Forage rice . Water management . Methanogenic archaea . Dry-thermophilic anaerobic digestion . Biogas residue
1 Introduction Biogas production from agricultural waste is an effective strategy for waste management because it produces energy and mitigates greenhouse gas emissions (Arthurson 2009). Among the biogas production methods, dry anaerobic digestion has received great attention in recent years. It is generally carried out with a higher solids content (>10 %) than that used in wet anaerobic digestion, and it treats larger volumes of wastes (Jha et al. 2011). Because dry thermophilic anaerobic digestion (DTAD) process generates a solid residue, beneficial use of the residue is important in terms of material cycling. In a previous study, Zhou et al. (2013) conducted experiments on DTAD of swine manure (pig dung+urine) combined with forage rice straw and showed that stable fermentation occurred in this system. If this residue can be used in forage rice
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fields as fertilizer, harvested rice can be used as pig feed. The remaining leaves and stems can be treated in DTAD as organic carbon source. Thus, DTAD and forage rice production could represent a sustainable pig manure treatment system. Rice fields are a major contributor to methane (CH4) emissions. According to estimates by the United States Environmental Protection Agency (US-EPA), CH4 emissions from rice paddy fields account for approximately 7 % of anthropogenic global CH4 emissions (US-EPA 2012). In rice soil, CH4 is produced by methanogenic archaea from either H2/CO2 or acetate, which are products of anaerobic decomposition of organic matter (Le Mer and Roger 2001). Therefore, DTAD residue application in forage rice fields would provide organic carbon for growth of methanogenic archaea. Forage rice needs more nitrogen than food rice to support high biomass production (Kyaw et al. 2005). Because whole crop is utilized as a feed for pig or cattle, returning pig or cattle waste is important for nutrient management in forage rice cultivation. It has been reported that more applications of organic waste increased biomass as well as greenhouse gas emission from forage rice fields (Sasada et al. 2011; Riya et al. 2012; Win et al. 2010). Sasada et al. (2011) found that application of anaerobically digested cattle/pig slurry caused higher CH4 emission than that by the application of a chemical fertilizer. On the other hand, Riya et al. (2012) observed a rapid increase in CH4 fluxes after topdressing with liquid cattle waste. While liquid organic waste contained mineral nitrogen and labile carbon, DTAD residue contained more organic nitrogen and carbon. In addition, the residue should be applied before transplanting, at one time, as straw or compost incorporation. Therefore, DTAD application in forage rice paddy fields may differently affect soil physicochemical properties and exhibit a different pattern and intensity of CH4 emission from organic liquid waste application. However, no information about relationship between dynamics of CH4 flux and environmental factors in a forage rice field incorporated with DTAD residue is available. Water management is important for rice production and also has the potential to mitigate CH4 emissions (Yagi et al. 1996; Zou et al. 2005). In a rice field managed by midsummer drainage and
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intermittent irrigation, CH4 emissions during cultivation period are mitigated by 65 % and 36 % with and without wheat straw incorporation, respectively (Zou et al. 2005). Recent review determined that CH4 emission in continuously flooded rice fields is as much as 90 % higher compared with other water management methods, independent from straw incorporation (Sanchis et al. 2012). Thus, water management is effective to mitigate CH4 emission in a rice field amended with organic matter. Although there have been many reports about effectiveness of water management on CH4 emission, contrasting results have been reported about response of methanogenic archaea to water management. For example, Jiao et al. (2006) reported lower number of methanogens in a paddy soil managed by intermittent irrigation than in those managed by continuous flooding, while Watanabe et al. (2013) showed no clear reduction of methanogenic archaea. Therefore, the effect of water management on CH4 mitigation as well as abundance of methanogenic archaea should be evaluated in a forage rice field applied with DTAD residue. Riya et al. (2012) found a rapid increase in nitrous oxide (N2O) emission, a potent greenhouse gas that has 298-times higher global warming potential than that by CO2 (IPCC 2007), during drainage after an application of liquid cattle manure. N2O emission during drainage is widely reported for rice fields (Ma et al. 2007; Zou et al. 2005). This impact on total greenhouse gas emission is emphasized especially for high N-fertilized rice fields (Riya et al. 2012). According to our system analysis, forage rice fields should receive about 300 kg N·ha−1 of DTAD residue for production of forage for pig and utilization of the residue (see Subsection 2.1). This nitrogen rate is about three times higher than the Japanese conventional nitrogen fertilization rate (100 kg N ha−1; Nishimura et al. 2004). Therefore, the combined global warming impact of CH4 and N2O should be evaluated. The objective of this study was to clarify the effects of incorporating DTAD residue on greenhouse gas emissions from a forage rice field and to determine whether water management could mitigate these effects. Therefore, we added DTAD residue to a forage rice field and compared the effects of local water management and intermittent irrigation
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strategies on greenhouse gas emissions. To confirm the impact of DTAD residue application and water management on CH4 emission, several environmental factors affecting CH4 production, functional gene of methanogenic archaea, and plant parameters were also measured.
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planting density of 18 hills·m−2 on May 29 (0 days after transplanting [DAT]). Midsummer drainage was conducted in all treatments from July 10 to 16 (42–48 DAT). Intermittent irrigation was conducted from 48 to 106 DAT in RI. Final drainage to dry the soil was carried out on September 11 (106 DAT). Rice plants were harvested on October 13 (137 DAT). 2.2 Preparation of DTAD Residue
2 Materials and Methods 2.1 Study Site and Experimental Layout The field study was carried out in a local farmer’s rice field (1,000 m2) in the city of Namegata, Ibaraki Prefecture, Japan (36°7′ N, 140°23′ E) in 2013. The soil was classified as a sandy loam soil. The total carbon and total nitrogen contents were 0.90 % and 0.04 %, respectively, in the 0–5 cm layer of soil, and 1.11 % and 0.10 %, respectively, in the 5–20 cm layer of soil. We applied three treatments: (a) CC, 100 kg N· ha−1 chemical fertilizer (NH4+, P2O5, and K2O, each 8 %) and continuous flooding; (b) RC, 300 kg N·ha−1 DTAD residue (on a total N basis) and continuous flooding; and (c) RI, 300 kg N·ha−1 DTAD residue and intermittent irrigation. The total organic carbon in the residue was 5496 kg C·ha−1. Nitrogen fertilization rate in CC is based on conventional management of rice, whereas the amount of 300 kg N ha−1 in RC and RI is determined from the treatment of DTAD residue generated from DTAD facility treating manure from 1,000 pigs. In the calculations, the area of forage rice paddy field was estimated from land area required to supply forage for 1,000 pigs. Therefore, this study examined greenhouse gas (GHG) emissions when using DTAD residue in the management of forage rice fields. In the experimental rice field, nine plots, each 1 m×3 m, were constructed by inserting a plastic frame into the hard subsoil layer. The frame was 15 cm high above the soil surface. Each treatment was assigned three plots. Chemical fertilizer and DTAD residue as basal fertilizer were applied at a rate of 100 kg N ha−1 in CC and 300 kg N ha−1 in RC and RI on May 22. No topdressing was applied during cultivation. The DTAD residue was mixed in at 0–10 cm depth. Rice seedlings of Takanari (cultivar of Oryza sativa L.) were transplanted at a
A semi-batch digester was constructed to prepare the DTAD residue. Pig manure was co-digested with forage rice straw at 55 °C, in a 73 % water content, and for 30–40 days of sludge retention time in the digester. The inoculum used for digestion was taken from a digester used for DTAD of food waste, paper, and twigs. The degradation rate of volatile solids during digestion was approximately 50 %. The DTAD residue was prepared by drying fresh DTAD residue in N2 atmosphere to degrade readily decomposable residual organic matter and to improve handling and storage. The total carbon and nitrogen contents of the residue were 30.3 % and 1.69 % (on a wet weight basis), respectively. The C/N ratio was close to 18. 2.3 Measurement of CH4 and N2O Emissions Fluxes of CH4 and N2O were evaluated using the closed chamber method (Riya et al. 2012). Three chamber bases (each 0.40 m long, 0.20 m wide, and 0.20 m high) were inserted to a depth of approximately 5 cm in each plot 1 h before gas sampling. The chamber base had a water channel to make the gas chamber airtight. The chambers were equipped with a thermometer, pressure-adjusting bag, fan, and three-way stopcock. Gas samples were withdrawn at 0, 10, and 20 min after the chambers were set on their bases and were transferred to pre-evacuated glass vials (SVG-10, Nichiden-Rika Glass Co. Ltd., Hyougo, Japan). During gas sampling, water table and soil Eh (see later) were measured. Methane concentration in gas samples was analyzed using GC-14B gas chromatograph with a flame ionization detector (Shimadzu, Kyoto, Japan), and N2O concentrations were measured using GC-14A gas chromatograph with an electron capture detector (Shimadzu, Kyoto, Japan). The gas flux from each plot to the
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atmosphere was calculated using Eq. (1) based on an increase in gas concentration in the chamber over time: F ¼ ΔC=Δt V=V0 T0 =T M 1=A ð1Þ
where F is the flux of CH4 or N2O (g·m−2 ·h−1), ΔC/Δt is the change in CH4 or N2O concentration in the chamber per unit time (ppmv · h−1), V is the volume of the chamber (m3), V0 is the molar volume of ideal gas (0.0224 m3 ·mol−1), T0 is 273 K, T is the air temperature in the chamber (K), M is the molar
CO2 −eq ¼
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weight of CH 4 or N2 O (g · mol −1), and A is the sectional area of the base (m2). Cumulative CH4 and N2O emissions during cultivation period were estimated by trapezoidal integration of the mean flux over time. To evaluate the global warming impact of forage rice fields, we calculated the cumulative CO2-equivalent (CO2-eq) emission using the 100-year global warming potential (25 for CH4; 298 for N2O) (IPCC 2007), as follows:
. . . 25 ECH4‐C 16 12 þ 298 En2O‐N 44 28 1000
where CO2-eq is the cumulative CO2-eq emission (t CO2 ·ha−1), and ECH4–C and EN2O–N are cumulative CH4–C and N2O–N emissions (kg·ha−1), respectively. 2.4 Measurement of Environmental Factors To measure soil Eh at 5 cm depth, two platinum electrodes (EP-201, Fujiwara Scientific Co. LTD., Tokyo, Japan) were permanently installed in each plot. Soil Eh was measured using a portable Eh meter (PRN-41, DKK-TOA Corporation, Tokyo, Japan) with a platinum electrode connected to an Ag/AgCl reference electrode (4400, DKK-TOA Corporation). At the time of rice transplanting, two porous cups (DIK-8390, Daiki Rika, Saitama, Japan) were permanently inserted at 5 cm depth in each plot. During the experimental period, pore water was periodically sampled from the cups using a syringe. Sampled pore water was filtered through a 0.45-μm membrane filter and stored at 4 °C until analysis. Dissolved organic carbon (DOC) concentrations were measured with a total organic carbon analyzer (TOC 5000A; Shimadzu). Concentrations of NH4+ and NO3− were analyzed by using ion chromatography (ICS-90 for NH4+ and ICS-1000 for NO3−; Dionex, Sunnyvale, CA, USA). 2.5 Analysis of mcrA Copy Number in the Soil Three soil cores (at 0–5 cm depth) were collected on 34, 79, 113, and 137 DAT from each plot for molecular
ð2Þ
biological analyses and stored at 4 °C until DNA extraction. Total DNA was extracted from soil samples using Extrap Soil DNA Kit Plus ver. 2 (Nippon Steel & Sumikin Eco-Tech Corporation, Tokyo, Japan) according to the manufacturer’s protocol. Real-time PCR was carried out using CFX96 real-time PCR system (Bio-Rad, Hercules, CA, USA) to determine the mcrA copy number using primers mlas and mcrA-rev (Steinberg and Regan 2009). Each reaction was performed in 20 μL aliquots containing 10 μL Sso FastTM EvaGreen Supermix (Bio-Rad), 0.5 μL of each forward and reverse primer, 5.0 μL DNA sample, and 4.0 μL MilliQ water. The conditions for real-time PCR were as follows: preheating at 94 °C for 300 s, followed by 40 cycles of denaturation at 94 °C for 25 s, annealing at 65 °C for 30 s, and elongation at 72 °C for 45 s. A melting curve analysis was conducted by increasing the temperature from 65 °C to 95 °C at 0.5 °C increments every 5 s. Measurements were performed in triplicate. 2.6 Rice Plants A single rice plant including root was randomly taken from each plot at 34, 79, and 113 DAT to measure aboveground biomass and root biomass. At harvest (137 DAT), aboveground biomass of 18 rice plants were harvested from each plot to determine the yield of rice plants. One of the 18 rice plants was randomly selected as a rice plant to be used for growth parameter determination. Weight of the aboveground and root biomass was determined after air-drying.
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2.7 Statistical Analysis One-way analysis of variance (ANOVA) was performed to analyze the variation in greenhouse gas emissions and yield of harvested rice plants among treatments. Significant difference between different treatments and between different days of treatment was analyzed for mcrA copy number and plant growth parameters, respectively, by least significant difference test. Correlation analyses were carried out between DOC concentration and CH4 flux for a given period. All statistical analyses were performed using SPSS v.16.0 (SPSS Inc., USA).
3 Results 3.1 Methane and Nitrous Oxide Fluxes In CC treatment, CH4 flux gradually increased from 0.5 to 5.8 mg C·m−2 ·h−1 before the midsummer drainage (Fig. 1). CH4 fluxes in RC and RI were greater than those in CC, fluctuating between 6.5 and 42.3 mg C· m−2 ·h−1. However, during midsummer drainage, CH4 fluxes decreased to 0.3–2.2 mg C m−2 ·h−1. From 48 to 106 DAT, CH4 flux in CC again gradually increased. CH4 fluxes in RC and RI increased more rapidly than those in CC. The increase in CH4 flux in RI was smaller than that in RC from 48 to 106 DAT. During the entire cultivation period, N2O fluxes fluctuated between −24.7 and 13.9 μg N m−2 ·h−1 (data not shown). These values were within the detection limit (58 μg N m−2 ·h−1). Therefore, N2O fluxes were considered as zero throughout the cultivation period. 3.2 Cumulative Greenhouse Gas Emissions In CC, the cumulative CH4 emission was 105 kg C ha−1, significantly lower than in RC (509 kg C ha−1; Table 1). The cumulative CH4 emission in RI was 306 kg C ha−1, approximately 60 % of that in RC. Table 1 also shows CO2-eq for each treatment, calculated from CH4 emission values and the 100-year global warming potential factor. N2O emissions were not included in the calculations, as mentioned above. The lowest CO2-eq was 3.5 t CO2 ha−1 in CC. CO2-eq values in RC and RI were 17.0 and 10.2 t CO2 ha−1, respectively. The fluctuation in CO2-eq values among
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the treatments had the same trend as the one in CH4 emissions. 3.3 Environmental Factors The changes in DOC and NH4–N concentrations in the pore water at 5 cm soil depths are shown in Fig. 2a, b, respectively. In CC, DOC concentration at 5 cm depth gradually decreased from 23 mg C L−1 (7 DAT) to 9.2 mg C L−1 (43 DAT); then, after the midsummer drainage, it gradually increased to 23 mg C L−1 (97 DAT). In RC and RI, DOC concentrations were higher than those in CC. At the first sampling time (7 DAT), DOC concentration was 150 mg L−1 in RC and RI, six times higher than in CC, and it decreased over time. DOC at 5 cm soil depth in RC and RI sharply decreased during the midsummer drainage to levels similar to that in CC. After the midsummer drainage, DOC concentration increased to 40 mg C L−1 at 72 DAT, with a concomitant increase in CH4 flux (Figs. 1a and 2a). In CC, NH4–N levels decreased from 38 mg N L−1 at 7 DAT to near zero at 34 DAT (Fig. 2b). Concentrations of NH4–N in RC and RI were less than 10 mg N L−1 at 7 DAT and reached near zero at 34 DAT. No obvious changes were observed during the remaining period. NO3–N was not detected during the cultivation period (data not shown). Figure 3a, b shows seasonal changes in the water table and soil Eh at 5 cm soil depth, respectively. Before the midsummer drainage, soil Eh showed negative values; the average soil Eh was −109±21, −163±18, and −135±47 mV in CC, RC, and RI, respectively. During the midsummer drainage, soil Eh increased to approximately +600 mV. After the midsummer drainage, when continuous flooding in CC and RC and intermittent irrigation in RI began, the average soil Eh was 31±102, −84±56, and 80±197 mV in CC, RC, and RI, respectively. In RC, soil Eh continued to decrease to −144 mV, while in RI, soil Eh increased from 72 DAT and fluctuated around values higher than 0 mV. Figure 4a shows correlation between DOC concentration and CH4 flux at different periods. In all sampled periods, CH4 flux showed positive correlation with DOC concentration. In contrast, the slope of the regression line became steeper from before-midsummer drainage to after-midsummer drainage. Figure 4b shows the relationship between soil Eh and CH4 flux. Higher CH4 fluxes were distributed around −200 mV, especially in
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Fig. 1 Seasonal changes in CH4 fluxes during the cultivation period. Double-headed arrows indicate drainage period. Intermittent irrigation was carried out from 48 to 106 DAT in RI
RC and RI, whereas lower CH4 fluxes were found in soil with higher Eh value. 3.4 mcrA Gene Copy Number In all treatments, mcrA gene copy number increased with time (Fig. 5). However, these numbers differed among treatments. At 34 DAT, there was no significant difference between the treatments. In CC treatment, a large increase in mcrA copy number was observed between 79 and 113 DAT. After a rapid increase in CH4 flux in RC and RI on 72 DAT (Fig. 1), significant difference in mcrA gene copy number was detected in CC and DTAD residue amended plots (RC and RI) on 79 DAT.
average biomass of harvested plants was 76.5, 51.5, and 39.2 g per plant. Root biomass showed a similar trend in all treatments (Fig. 6b). Maximum root weight was observed at 79 DAT: 29.4, 23.1, and 15.6 g per plant in CC, RC, and RI, respectively. Afterwards, the root biomass decreased. Table 2 shows the yield of rice determined by weight of 18 rice plants harvested from each plot. Treatment CC has the highest yield of 15.2 t·ha−1, followed by RC and RI. In RC and RI, the ratio of grain to total biomass was also lower than in CC.
4 Discussion 4.1 Influence of DTAD Residue Incorporation and Water Management on Dynamics of CH4 Flux
3.5 Forage Rice Growth Aboveground biomass sharply increased until harvest (Fig. 6a). On 34 DAT, the aboveground biomass was 15.7, 3.3, and 2.3 g per plant in CC, RC, and RI, respectively. On 113 DAT, these values were 97.7, 144, and 91.7 g per plant, respectively. Finally, the Table 1 Cumulative greenhouse gas emissions during experimental period Treatmenta
CH4 emission (kg C ha−1)
CO2-eqb (t CO2 ha−1)
CC
105±38a
3.5±1.3a
RC
509±145b
17.0±4.8b
RI
306±44c
10.2±1.5c
To date CH4 emissions from rice fields incorporated with wheat straw, rice straw, and composts have been intensely studied (Ma et al. 2007; Wang et al. 2000; Watanabe et al. 1999; Yagi and Minami 1990). Values of CH4 flux from forage rice fields incorporated with DTAD residue were consistent with those reported in previous studies. We observed two active CH4 emission stages; one is before midsummer drainage (7–43 DAT) and another is after midsummer drainage (45–97 DAT). Because organic matter is a substrate for CH4 production, DOC is an important indicator of CH4 emission (Lu et al. 2000b). However, in rice fields amended with organic matter, the relationship between DOC concentration and CH4 flux has been rarely reported. In Fig. 4a,
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Fig. 2 Seasonal changes in a DOC and b NH4–N concentrations at 5 cm soil depth. Double-headed arrows indicate drainage period. Intermittent irrigation was carried out from 48 to 106 DAT in RI
different slopes of the regression lines at different periods suggest that the quality of DOC and environment for CH4 production changes with time. There have been several reports of temporal changes in the source of CH4 emitted from rice fields incorporated with rice straw (Chidthaisong and Watanabe 1997; Watanabe et al. 1998). Watanabe et al. (1999) found that the contribution of incorporated rice straw to CH4 emission was higher in the early cultivation period, while in later stages, the main source of CH4 shifted to plant-derived material such as root exudate and dead leaf or root. Before midsummer drainage (between 7–43 DAT), high DOC concentrations were detected in DTAD amended plots (RC and RI; Fig. 2a) implying that the degradation of DTAD has occurred. In anaerobic soils, methane fermentation is a final process of a stepwise degradation of organic matter. During degradation, several kinds of monomers are produced by hydrolysis, acidogenesis, and acetogenesis (Le Mer and Roger 2001). Therefore,
a portion of DOC before midsummer drainage in RC and RI would not be directly related to CH4 production (Fig. 4a). Low DOC concentration but rapid increase in CH4 flux after midsummer drainage suggest that organic matter in the pore water is converted more efficiently into CH4 in DTAD residue-incorporated plots. A concurrent increase in mcrA copy number, above-ground and root biomass, and CH4 flux in RC after 72 DAT (Figs. 1, 5, and 6) suggests a link between the population of methanogenic archaea and plant growth and CH4 production. Rice roots release exudates into the rhizosphere, and the amount of exudates increases with plant growth (Lu et al. 2000b). Methane production in anaerobic soils amended with exudates was completed within 5 days after treatment (Lu et al. 2000a). Thus, we speculate that forage rice growth after midsummer drainage in RC and RI provides exudates that are
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Fig. 3 Seasonal changes in a water table and b soil Eh at 5 cm soil depth. Double-headed arrows indicate drainage period. Intermittent irrigation was carried out from 48 to 106 DAT in RI
efficiently converted to CH4 in anaerobic soils rich in methanogenic archaea. Furthermore, Watanabe et al. (1998) suggested that a part of the once assimilated
CO2–C, which originates from decomposition of incorporated rice straw, would be emitted as CH4 in later growth stages. In addition, Yuan et al. (2014) reported
Fig. 4 Relationship between CH4 flux and a DOC concentration at different periods and b soil Eh in different treatments. MD indicates midsummer drainage. Dotted, gray, and black lines are
regression lines between DOC concentration and CH4 flux before, during, and after midsummer drainage, respectively
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Fig. 5 Seasonal changes in mcrA gene copy number. Different letters indicate significant differences among the treatments for each sampling day (p
