Abstract
In Japan, it is important to recycle the nutrients in manure for forage production because most dairy cattle are fed inside, mainly with imported grain and home-grown roughage. To understand the overall effect of manure use on grassland on the net greenhouse gas (GHG) emission and GHG intensity of herbage production systems, the integrated evaluation of emissions of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) is essential. The objective of this study was to compare the net GHG emissions (expressed in CO2-eq ha−1 y−1) and GHG intensity (expressed in CO2-eq Mg–1 dry matter yield) of herbage production based on manure slurry + synthetic fertilizer (slurry system) with that based on farmyard manure + synthetic fertilizer (FYM system). Calculations of net GHG emissions and GHG intensity took into account the net ecosystem carbon balance (NECB) in grassland, the CH4 and N2O emissions from grassland, and GHG emissions related to cattle waste management, synthetic fertilizer manufacture, and fuel consumption for grassland management based on literature data from previous studies. The net GHG emissions and GHG intensity were 36% (6.9 Mg CO2-eq ha−1 y−1) and 41% (0.89 Mg CO2-eq Mg−1), respectively, lower in the FYM system.
1. Introduction
Recent greenhouse gas (GHG) profiles of the agriculture sector in Japan show that major GHG sources in terms of carbon dioxide equivalents (CO2-eq) are rice cultivation (methane (CH4), 41%), enteric fermentation (CH4, 22%), manure management (CH4 and nitrous oxide (N2O), 19%), and soils (N2O, 16%) []. In Japan, most dairy cattle are fed inside, mainly with imported grain and home-grown roughage. Around 70% of the dairy cattle waste is composted [] for use in crop and forage production. Therefore, it is important to apply manure to meadows and pastures, which account for 13.4% of the total agricultural land area of Japan []. In the year 2015, 570,475 Mg-N y−1 was excreted by livestock in Japan, of which 304,285 Mg-N y−1 was applied to agricultural soil (4,496,000 ha) [].
The application of farmyard manure (FYM) to grassland increases the net ecosystem carbon balance (NECB) relative to manure slurry application []. This is mainly because the amount of C input to grassland from FYM is greater than that from slurry, but the decomposition of FYM is slower than that of slurry []. Consequently, FYM application has a greater potential to improve the C stock in grassland soil than slurry application. However, emissions of CH4 and N2O from manured grassland [] need to be considered in evaluating the overall effect of manure application on the net GHG emissions from grassland []. The soil of grassland usually acts as a sink of atmospheric CH4, and manure application only temporarily increases CH4 emission from grassland []. In contrast, N2O emission increases with increasing the N surplus in grassland soil []. Therefore, judicial application of organic and inorganic N is necessary to mitigate the N2O emission from grassland []. Cattle waste management, including slurry storage [] and composting [], is another source of GHG, and in addition to CH4 and N2O emissions from cattle waste management, farm machinery used for composting FYM also emits CO2 []. To maintain productive sward, supplemental fertilizers are used to make up for nutrient insufficiencies in manure (e.g., N and P in the case of cattle manure) [], but their manufacture also emits GHG []. Furthermore, GHG emissions from fuel consumption for grassland management also need to be taken into consideration [].
To assess the net GHG emissions (i.e., integrated evaluation of CO2, CH4 and N2O) and GHG intensity (GHGI) of herbage production systems, an integrated evaluation of the above processes is necessary (Table S1). On that basis, the identification of important processes with significant contributions is necessary in order to determine the priority of countermeasures to mitigate GHG. To date, it is recognized that the quality and quantity of organic materials applied have great influence on soil organic carbon [,]; however, insufficient information is available on the effect of manure type (i.e., slurry or FYM) on the net GHG emissions and GHGI of herbage production systems.
The objectives of this study were: (1) to investigate the net GHG emissions (expressed in CO2-eq ha–1 y−1) and GHGI (expressed in CO2-eq Mg–1 dry matter yield) of herbage production systems based on manure slurry + synthetic fertilizer (slurry system) and on FYM + synthetic fertilizer (FYM system); (2) to show the relative contributions of each process in GHG emission; and (3) to show how farming practices can be adjusted to minimize emissions. My hypotheses were that the FYM system reduces the net GHG emissions in comparison with the slurry system, and that the contributions of grassland soil and cattle waste management to the net GHG emissions of herbage production systems are greater than the other processes.
2. Materials and Methods
2.1. System Boundary and Functional Units
The system boundary comprised the following processes: the NECB in grassland, emissions of CH4 and N2O from grassland, and GHG emissions related to cattle waste management (i.e., slurry storage and composting FYM), synthetic fertilizer manufacture, and fuel consumption for grassland management operations. The functional unit was defined as ha−1 y−1 of grassland or Mg−1 of dry matter yield. The study did not take into account the GHG emissions related to the manufacture of farm machinery and buildings, transport of synthetic fertilizers, or indirect N2O emissions related to leaching of nitrate (NO3−) and redeposition of volatilized ammonia (NH3).
2.2. NECB and Emissions of CH4 and N2O from Grassland
The NECB and emissions of CH4, and N2O from grassland (1 ha) treated with slurry (65.8 to 66.4 Mg ha−1 y−1) or FYM (36.5 to 39.2 Mg ha−1 y−1) were based on previous studies [,] in which slurry or FYM was applied to the upper limit based on K requirement for herbage production. Annualized values of NECB, emissions of CH4, and N2O were calculated by averaging the information of two years.
2.3. GHG Emissions Related to Cattle Waste Management
Emissions of CH4 and N2O from stored slurry were calculated from emission factors (EFs, 3.90% and 0.02%, respectively) in Japan []. Emissions of CH4 and N2O from composting of applied FYM were estimated from a farm study [] and EFs (3.8% and 2.38% to 2.39%, respectively) in Japan []. Biogenic CO2 losses from manure were excluded (i.e., C neutral), but emissions of CO2 due to the consumption of electricity or fuel for composting FYM were estimated from a farm study [] and EFs []. Emissions of CH4, N2O and CO2 per unit area of grassland (1 ha) were calculated by multiplying these emissions per unit weight of slurry or FYM and the weight of slurry or FYM annually applied to grassland (Mg ha−1 y−1).
2.4. GHG Emissions Related to Synthetic Fertilizer Manufacture
GHG emissions from the manufacture of N and P fertilizers were estimated from the SimaPro 7.1 database (PRé Consultants, Amersfoort, Netherlands). Emissions of CH4, N2O and CO2 per unit area of grassland (1 ha) were calculated by multiplying these emissions per unit weight of synthetic fertilizer and the weight of synthetic fertilizer annually applied to grassland (kg ha−1 y−1). No K fertilizer was used, because the applied slurry or FYM covered the K requirement for herbage production [,].
2.5. GHG Emissions Related to Grassland Management
GHG emissions due to fuel consumption by farm machinery for loading and spreading of manure and fertilizers and for cutting and harvesting of herbage were estimated from a previous Japanese study in the 1990s [] and EF []. The emission of CO2 per unit area of grassland (1 ha) was calculated by multiplying the fuel consumption per unit of operation, the operation unit necessary for management of grassland (1 ha), and EF.
2.6. Overall Net GHG Emissions and GHGI of Herbage Production
Emissions of CH4 and N2O were converted to CO2-eq by using values of the 100-year global warming potential, assumed to be 1 for CO2, 25 for CH4, and 298 for N2O []. The net GHG emissions (CO2-eq ha–1 y−1) were calculated by considering the NECB and emissions of CH4 and N2O from grassland (Section 2.2.) and the GHG emissions related to cattle waste management (Section 2.3.), synthetic fertilizer manufacture (Section 2.4.), and grassland management (Section 2.5.) on an area basis. The GHGI (CO2-eq Mg–1) was calculated by dividing the net GHG emissions by the dry matter yield of grassland receiving slurry or FYM [].
3. Results and Discussion
3.1. NECB and Emissions of N2O and CH4 from Grassland
The NECB of the slurry system (−12.8 Mg CO2-eq ha−1 y−1) was far lower than that of the FYM system (−1.8 Mg CO2-eq ha−1 y−1); that is, the FYM system contributed more to improving the C stock in grassland than the slurry system (Figure 1). (Please note that negative NECB values represent net CO2 emission from grassland to the atmosphere.) The NECB of the slurry and FYM systems were similar to previously measured values in Japanese grasslands that respectively received only synthetic fertilizers or FYM + synthetic fertilizers [], suggesting that slurry C had limited capacity for maintaining soil organic C in comparison with FYM C []. The emissions of N2O from grassland were not significantly different between slurry and FYM systems (2.2 Mg CO2-eq ha−1 y−1 in slurry system, 2.3 Mg CO2-eq ha−1 y−1 in FYM system), because synthetic N fertilizer was also applied [,]. The emissions of CH4 were much smaller than those of CO2 and N2O (+0.034 Mg-CO2-eq ha−1 y−1 in slurry system, −0.032 Mg-CO2-eq ha−1 y−1 in FYM system).
Figure 1.
Annualized emissions of CO2 (NECB), N2O and CH4 from grassland receiving manure + fertilizer.
3.2. GHG Emissions Related to Cattle Waste Management
The GHG emissions related to cattle waste management were due mainly to CH4 (2.9 Mg CO2-eq ha−1 y−1, Table 1) in the slurry system and to both CH4 (4.2 Mg CO2-eq ha−1 y−1, Table 2) and N2O (2.0 Mg CO2-eq ha−1 y−1, Table 3) in the FYM system (Figure 2). The emission of CO2 related to energy consumption (0.15 Mg CO2-eq ha−1 y−1, Table 4) was smaller than the emission of CH4 and N2O by composting. This is because the amount of CO2 emission for composting 1 Mg of FYM was only 4.1 kg. The emission of N2O by slurry storage (0.028 Mg-CO2-eq ha−1 y−1, Table 5) was much smaller than the emission of N2O by composting FYM (2.0 Mg CO2-eq ha−1 y−1, Table 3), mainly due to the small EF for slurry storage (0.02%) in comparison with composting FYM (2.4%).
Table 1.
Emission of CH4 related to storage of dairy cattle slurry.
Table 2.
Emission of CH4 related to composting.
Table 3.
Emission of N2O related to composting dairy FYM.
Figure 2.
Annualized emissions of N2O, CH4, and CO2 related cattle waste management.
Table 4.
Emission of CO2 related to energy consumption for composting dairy FYM.
Table 5.
Emission of N2O related to storage of cattle slurry.
3.3. GHG Emissions Related to Fertilizer Manufacture
The GHG emission related to fertilizer manufacture in the FYM system (1.5 Mg CO2-eq ha−1 y−1, Table 6) was almost double that for the slurry system (0.82 Mg CO2-eq ha−1 y−1, Table 6), mainly owing to the difference in N application rate. Slurry contains substantial amount of readily available N, however, most of N in FYM is in organic form. Therefore, the amount of N fertilizer supplemented to grassland in FYM system (159 to 177 kg-N y−1) was greater than that in slurry system (90 kg-N y−1).
Table 6.
Emissions of GHG related to synthetic fertilizer manufacture.
3.4. GHG Emissions Related to Grassland Management
The GHG emissions related to grassland management were similar between the FYM and slurry systems (0.49 vs. 0.47 Mg CO2-eq ha−1 y−1, Table 7), because the herbage yields were not significantly different between the slurry (8.8 Mg y−1) and FYM (9.5 Mg y−1) systems. The GHG emissions related to grass cutting, turning and harvesting, bailing and wrapping were greater than those related to loading and spreading of slurry or FYM. This is mainly because slurry and FYM were spread twice and once a year, respectively; however, grass cutting, turning and harvesting, bailing and wrapping was performed four times a year in both the slurry and FYM systems.
Table 7.
Emission of CO2 related to fuel consumption for grassland management and transport.
3.5. Overall Net GHG Emissions and GHGI
The net GHG emissions was 19 Mg CO2-eq ha−1 y−1 in the slurry system and 12 Mg CO2-eq ha−1 y−1 in the FYM system (Figure 3). The GHGI was 2.2 Mg CO2-eq Mg−1 in the slurry system and 1.3 Mg CO2-eq Mg−1 in the FYM system. Thus, the net GHG emissions of the FYM system was 36% (6.9 Mg CO2-eq ha−1 y−1) less and the GHGI of the FYM system was 41% (0.89 CO2-eq Mg−1) less than that of the slurry system.
Figure 3.
Annualized overall net GHG (greenhouse gas) emissions from herbage production.
The contribution of grassland soil, cattle waste management, fertilizer manufacture and grassland management to the net GHG emissions were 78% (CO2: 66%, N2O: 11% and CH4: 0.2%), 15% (CO2: 0.0%, CH4: 15%, N2O: 0.1%), 4% and 2% in the slurry system, and 33% (CO2: 14%, N2O: 19% and CH4: −0.3%), 51% (CO2: 1%, N2O: 16%, CH4: 34%), 12% and 4% in the FYM system, respectively. These results collectively suggest that NECB and the N2O emissions from grassland and the CH4 and N2O emissions related cattle waste management are crucial to the control of net GHG emission and GHGI.
The FYM system reduced the net GHG emissions and GHGI relative to the slurry system (Figure 3). The net reduction was due largely to the improvement of C stock in grassland (Figure 1). Although the emissions of GHG related to cattle waste management and fertilizer manufacture were greater in the FYM system than in the slurry system (Figure 3), the FYM system maintained an advantage in net GHG emissions and GHGI, due mainly to the difference in NECB in grassland (Figure 1)—that is, the persistent organic matter in FYM decomposed slowly in the soil and contributed to the improvement of C stock, but the labile organic matter in slurry decomposed quickly in the soil and was released to the atmosphere as CO2 []. Our results support the validity of FYM application for the mitigation of GHG emissions [,], not only from grassland, but also during herbage production. In the slurry and FYM systems, N and P were supplemented based on the fertilizer recommendation. Therefore, the yields in the slurry (8.8 Mg y−1) and FYM (9.5 Mg y−1) systems were comparable to the standard yield (8–10 Mg y−1) in Nasu, Japan [].
3.6. Adjustment of Farming Practices
These results show that the FYM system improved the net GHG emissions and GHGI relative to the slurry system (Figure 3). In Japan, a substantial amount of manure is derived from imported feed, and thus represents the net import of organic matter, which must be used with care for fertility management []. Making maximum use of manure in consideration of N, P, and K requirements for herbage production to reduce synthetic fertilizer rates to the absolute minimum is crucial to mitigating overall GHG emissions [,]. Applying manure and synthetic N fertilizer in excess of demand increases N2O emissions from grassland [,]. Therefore, the tightening of N application rates can limit overall GHG emissions. Mixing low-quality dried grass as a bulking agent into FYM reduced CH4 and N2O emissions [] and could further improve the C stock in grassland. For this goal, both the selection of appropriate methods for cattle waste management and the decision to base fertilizer application rates on the N supply from manure are crucial to reducing the net GHG emissions and GHGI.
4. Conclusions
The FYM system reduced the overall net GHG emissions and GHGI by 36% (6.9 Mg CO2-eq ha−1 y−1) and 41% (0.89 Mg CO2-eq Mg−1), respectively, relative to the slurry system. The net reduction was due largely to the improvement of C stock in grassland. Although the emission of GHG related to cattle waste management and supplemental fertilizer manufacture was greater in the FYM system than in the slurry system, the FYM system maintained an advantage. NECB and the N2O emissions from grassland and the CH4 and N2O emissions related to cattle waste management are crucial to the control of net GHG emissions and GHGI.
Supplementary Materials
The following is available online at http://www.mdpi.com/2073-4433/9/7/261/s1, Table S1: Calculation bases of greenhouse gas emissions.
Acknowledgments
This work was financially supported by the Ministry of Agriculture, Forestry and Fisheries of Japan through the “Development of technologies for mitigation and adaptation to climate change in Agriculture, Forestry and Fisheries” research project. The author thanks Ryusuke Hatano, Hokkaido University, and Kazuyuki Yagi, NARO, for their valuable discussion on the experimental design.
Conflicts of Interest
The author declares no conflict of interest. The funding body had no role in the collection, analyses, or interpretation of data, in the writing of the manuscript, or in the decision to publish the results.
References
- Greenhouse Gas Inventory Office of Japan (GIO). National Greenhouse Gas Inventory Report of Japan; Center for Global Environmental Research, National Institute for Environmental Studies: Tsukuba, Japan, 2017. [Google Scholar]
- Maeda, K.; Hanajima, D.; Morioka, R.; Toyoda, S.; Yoshida, N.; Osada, T. Mitigation of greenhouse gas emission from the cattle manure composting process by use of a bulking agent. Soil Sci. Plant Nutr. 2013, 59, 96–106. [Google Scholar] [CrossRef]
- Mori, A. Greenhouse gas sink-source functions of grassland ecosystems. Jpn. Agric. Res. Q. 2016, 50, 187–190. [Google Scholar] [CrossRef]
- Mori, A.; Hojito, M. Effect of dairy manure type on the carbon balance of mowed grassland in Nasu, Japan: Comparison between manure slurry plus synthetic fertilizer plots and farmyard manure plus synthetic fertilizer plots. Soil Sci. Plant Nutr. 2015, 61, 736–746. [Google Scholar] [CrossRef]
- Mori, A.; Hojito, M. Effect of dairy manure type and supplemental synthetic fertilizer on methane and nitrous oxide emissions from a grassland in Nasu, Japan. Soil Sci. Plant Nutr. 2015, 61, 347–358. [Google Scholar] [CrossRef]
- Shimizu, M.; Marutani, S.; Desyatkin, A.R.; Jin, T.; Nakano, K.; Hata, H.; Hatano, R. Nitrous oxide emissions and nitrogen cycling in managed grassland in Southern Hokkaido, Japan. Soil Sci. Plant Nutr. 2010, 56, 676–688. [Google Scholar] [CrossRef]
- Sawamoto, T.; Nakamura, M.; Nekomoto, K.; Hoshiba, S.; Minato, K.; Nakayama, M.; Osada, T. The cumulative methane production from dairy cattle slurry can be explained by its volatile solid, temperature and length of storage. Anim. Sci. J. 2016, 87, 827–834. [Google Scholar] [CrossRef] [PubMed]
- Fukumoto, Y.; Suzuki, K.; Waki, M.; Yasuda, T. Mitigation option of greenhouse gas emissions from livestock manure composting. Jpn. Agric. Res. Q. 2015, 49, 307–312. [Google Scholar] [CrossRef]
- Zhang, H.; Matsuto, T. Comparison of mass balance, energy consumption and cost of composting facilities for different types of organic waste. Waste Manag. 2011, 31, 416–422. [Google Scholar] [CrossRef] [PubMed]
- Snyder, C.S.; Bruulsema, T.W.; Jensen, T.L.; Fixen, P.E. Review of greenhouse gas emissions from crop production systems and fertilizer management effects. Agric. Ecosyst. Environ. 2009, 133, 247–266. [Google Scholar] [CrossRef]
- Pimentel, D. Handbook of Energy Utilization in Agriculture; CRC Press: Boca Raton, FL, USA, 1980. [Google Scholar]
- Bhogal, A.; Nicholson, F.A.; Rollett, A.; Taylor, M.; Litterick, A.; Whittingham, M.J.; Williams, J.R. Improvements in the quality of agricultural soils following organic material additions depend on both the quantity and quality of the materials applied. Front. Sustain. Food Syst. 2018, 2, 9. [Google Scholar] [CrossRef]
- Ito, N. Open type compost fermentation instrument. In The Report of Cost Research of Machines and Equipment for Livestock Waste Treatments 2002 (Undertake Research Project Commissioned by Livestock Industry’s Environmental Improvement Organization); Japan Livestock Production Facilities and Machineries Association: Tokyo, Japan, 2002; pp. 46–73. (In Japanese) [Google Scholar]
- National Institute for Agro-Environmental Sciences (NIAES). Manual for Life Cycle Assessment of Agricultural Practice in Japan; National Institute for Agro-Environmental Sciences: Tsukuba, Japan, 2003; pp. 1–51. (In Japanese) [Google Scholar]
- Sasaki, Y. Forage Crops, Specific Energy Consumption for Production Systems of Major Crops; Agriculture, Forestry and Fisheries Technical Information Society: Tokyo, Japan, 1996; pp. 361–383. (In Japanese) [Google Scholar]
- Intergovernmental Panel on Climate Change (IPCC). Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change; Climate Change 2007: The Physical Science Basis; Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K.B., Tignor, M., Miller, H.L., Eds.; Cambridge University Press: Cambridge, UK, 2007. [Google Scholar]
- Shimizu, M.; Marutani, S.; Desyatkin, A.R.; Jin, T.; Hata, H.; Hatano, R. The effect of manure application on carbon dynamics and budgets in a managed grassland of Southern Hokkaido, Japan. Agric. Ecosyst. Environ. 2009, 130, 31–40. [Google Scholar] [CrossRef]
- Handbook of Animal Waste Management and Utilization in Hokkaido 2004; Ohara, M., Takeda, Y., Omura, K., Eds.; Hokkaido Prefectural Experiment Stations and Hokkaido Animal Research Center: Sapporo, Japan, 2004. (In Japanese) [Google Scholar]
- Shiga, H.; Ohyama, N.; Maeda, K.; Suzuki, M. An evaluation of different organic materials based on their decomposition pattern in paddy soils. Res. Bull. Natl. Agric. Res. Cetr. 1985, 5, 1–19, (In Japanese with English Summary). [Google Scholar]
- Hirata, R.; Miyata, A.; Mano, M.; Shimizu, M.; Arita, T.; Kouda, Y.; Matsuura, S.; Niimi, M.; Mori, A.; Saigusa, T.; et al. Carbon dioxide exchange at four intensively managed grassland sites across different climate zones of Japan and the influence of manure application on ecosystem carbon and greenhouse gas budgets. Agric. For. Meteorol. 2013, 177, 57–68. [Google Scholar] [CrossRef]
- Shimizu, M.; Hatano, R.; Arita, T.; Kouda, Y.; Mori, A.; Matsuura, S.; Niimi, M.; Jin, T.; Desyatkin, A.R.; Kawamura, O.; et al. The effect of fertilizer and manure application on CH4 and N2O emissions from managed grasslands in Japan. Soil Sci. Plant Nutr. 2013, 59, 69–86. [Google Scholar] [CrossRef]
- Grassland Agriculture and Forage Seed Association (GAFSA). Agricultural activity and global warming. In Greenhouse Gas Mitigation by Self-Supplying Forage Production; Grassland Agriculture and Forage Seed Association: Tokyo, Japan, 2010; pp. 3–7. (In Japanese) [Google Scholar]
- Cardenas, L.M.; Thorman, R.; Ashlee, N.; Butler, M.; Chadwick, D.; Chambers, B.; Cuttle, S.; Donovan, N.; Kingston, H.; Lane, S.; et al. Quantifying annual N2O emission fluxes from grazed grassland under a range of inorganic fertiliser nitrogen inputs. Agric. Ecosyst. Environ. 2010, 136, 218–226. [Google Scholar] [CrossRef]
- Paustian, K.; Lehmann, J.; Ogle, S.; Reay, D.; Robertson, G.P.; Smith, P. Climate-smart soils. Nature 2016, 532, 49–57. [Google Scholar] [CrossRef] [PubMed]
© 2018 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).