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It is essential to reduce methane (CH4) emissions to minimize the contribution of global warming from rice paddies because CH4 contributes approximately 87% to the global warming potential (GWP). An increase in N fertilizer application could reduce CH4 emissions for several reasons: (1) affect the biomass enhancement of crops to store carbon, (2) decrease methanogenesis activity due to increased nitrate respiration, (3) occur nitrate- and nitrite-dependent anaerobic CH4 oxidation. According to the global scale meta-analysis, increasing N application reduces CH4 emissions. However, the reducing effect of nitrogen (N) fertilization on CH4 emissions from rice paddies needs to be confirmed. The changes in CH4 emission induced by N have a reasonably wide margin of error because the research results were not controlled for the direct factors related to CH4 emissions. Hence, although the increased N fertilizer can increase crop productivity and reduce GWP, it is not introduced as an appropriate agricultural practice. To elucidate the effects of N fertilization on CH4 emissions from rice paddies, field-based manipulation experiments were conducted in three regions where N fertilizer was applied under the control of the other factors. In addition, we aimed to identify why CH4 emissions differ depending on the amount of N fertilizer through the result of the microbial-mediated CH4 cycle.Urea was selected as N fertilizer and application rates were at 0, 90, 135, and 180 kg ha-1 (N0, N1, N2, and N3, respectively). Irrigation, rice species (Oryza sativa cv. Samkwang), cultivation period, and input of P, K, Ca, and Si fertilizer were identically managed in 3 sites in Miryang, Wanju, and Hwaseong for three years. DNA/RNA co-extraction was performed using three region’s soil samples in the 3rd year. Real-time qPCR was performed to quantify the mcrA and pmoA gene copy numbers to identify the abundances of methanogens and methanotrophs, respectively.Cumulative CH4 emissions increased with increasing N fertilizer in Miryang. In contrast, cumulative CH4 emissions significantly decreased with increasing N fertilizer application rates in Hwaseong and Wanju. Especially, N2 and N3 showed CH4 emissions lower than N0 in Hwaseong. In Wanju, the decrease in the abundance of mcrA and subsequently methanogenesis after N1 may cause a reduction in CH4 emissions, while in Hwaseong, the increase in quantification of pmoA and the subsequent higher CH4 oxidation may induce a decline in CH4 emissions. In Miryang, higher mcrA may promote methanogenesis and higher CH4 emissions with an increasing N application. The different responses in methanogens and methanotrophs with different N fertilizer application rates could be due to the initial N concentration. The correlation analysis between initial N including ammonium and nitrate and CH4 emissions from the literature showed a negative relationship at a global scale, suggesting the mechanism based on our experimental results is robust in global rice paddies.In conclusion, additional N fertilizer application considering the initial N concentration can not only increase crop yield in rice paddies but also reduce global warming by reducing CH4 emissions.

BACKGROUND: Methane (CH4) emission is calculated using the default CH4 emission factor as recommended by the International Panel on Climate Change(IPCC guidelines). However, the default emission factor has been derived using including the data from other countries having different soil and environmental conditions and may not reflect the real CH4 emission rates in Korea. The objective of this study was to estimate the baseline emission factor of CH4 in Korean paddy soils during rice cultivation. METHODS AND RESULTS: Methane emission patterns were characterized in four different paddy soils across country for a consecutive 3 years during the rice cultivation period. Rice plants were cultivated under continuous flooding and fertilized using the recommended chemical fertilization in Korea (N-P2O5-K2O=90-45-57kg/ha). The mean CH4 emission rate was 2.32 kg CH4/ha/day and the uncertainty of the investigated data was 21.7%, with a valuable error range at 1.82-2.82 kg CH4/ha/day with a 95% confidence interval. CONCLUSION(S): Conclusively, the Korean paddy soils' baseline emission factor of CH4 is approximately 2.32 kg CH4/ha/day and can be used to estimate the CH4 emissions more exactly.

This study was carried out to investigate the effects of the complex fertilizers containing polyaspartic acid (PAA) on growth and emission in rice field and optimum application rate of the fertilizer compared to the standard recommended application rate (control). The PAA-containing complex fertilizers (PCF) were applied at 55, 65 and 75% levels of standard recommended application rate (control). The application rate of PAA in the plot of every PCF treatment was 150g ai/10a. The PCF was applied as a basal dressing without topdressing at tillering stage. The growth parameters of rice and its nitrogen use efficiency treated with PCF at a 65 to 75% level were not different compared with those of control, and the rice yield was also not significantly different between PCF at a 65 to 75% level and control during 2 years(2010~2011) field experiment. And the -N content in soil was not affected by 65% to 75% level of PCF treatment. Considering overall research results such as rice yield and growth parameters PCF is not significantly different with the control and the optimum application rate of the PCF as a basal fertilization was determined to be 65~75% of the standard application rate based on the result in rice cultivation. Moreover, emission rate was significantly reduced by PCF treatments, showing 216 kg and 229 kg at 65% and 75% PCF treatment level, respectively, compared to 266 kg of the control.

BACKGROUND: Accurate estimates of total direct emissions from croplands on a country scale are important for global budgets of anthropogenic sources of emissions and for the development of effective mitigation strategies. Methane production resulted by the anaerobic decomposition of organic compounds where acts as inorganic electron acceptor. This process could be affected by the addition of rice straw, water management and rice variety itself. METHODS AND RESULTS: Rice (Oryza sativa L. Japonica type, var Samkwangbyeo) was cultivated in four plots: (1) Nitrogen-Phosphorus-Potassium (NPK) (:90-45-57 kg/ha); (2) NPK plus 3 Mg/ha rice straw (RS3); (3) NPK plus 5 Mg/ha rice straw (RS5); (4) NPK plus 7 Mg/ha rice straw (RS7) for 3 years (2010-2012) and the rice straw incorporated in fall (Nov.) in Gyeonggi-do Hwaseong-si. Gas samples were collected using the closed static chamber which were installed in each treated plot of . According to application of 3, 5, 7 Mg/ha of rice straw, methane emission increased by 46, 101, 190%, respectively, compared to that of the NPK plot. CONCLUSION(S): We obtained a quantitative relationship between emission and the amount of rice straw applied from rice fields which could be described by polynomial regression of order 2. The emission scaling factor estimated by the relationship were in the range of IPCC GPG (2000).

Increase in greenhouse gas emissions during the last century has led to remarkable changes in our environment and climate system. Many policy measures have been developed to reduce greenhouse gas emissions across the world, many of which require our lifestyle changes from energy-intensive to energy-saving. One of the changes in our living patterns is to consider food miles. A food mile is the distance food travels from where it is produced to where it is consumed. Providing information of food miles will help people choose low mileage food, helping promote a "green consumption" action and lead to a low carbon society with emission reduction systems. In this study, 10 items are selected from 23 Harmonized commodity description and 2-digit coding system (HS) to estimate their food miles, and emissions released in the transportation of imported food. For the estimation, four countries are chosen-Korea, Japan, United Kingdom (UK) and France, with Korea and Japan`s 2001, 2003, and 2007 trade statistics and UK and France`s 2003 and 2007 trade statistics used. As a result, Korea showed in 2007 the highest level of food miles and emissions per capita among 4 countries. That suggests that Korea should make an effort to purchase local food to reduce food miles and use low-carbon vehicles for food transport, contributing to reducing greenhouse gas emissions.

Increase of the greenhouse gases emissions during last century has led remarkable changes in our environment and climate system. Continuous monitoring of atmospheric constituents over the world is positively necessary to understand these changes around us. The concentrations of greenhouse gases () have been continuously measured at Global Climate Change Monitoring station in Gosan, Jeju since January, 2002. In this study, the variation characteristics of greenhouse gases as well as their annual, seasonal and diurnal trend using the data from January, 2002 to December, 2005 were analyzed. The raw data which was used in the analysis were validated with the methods recommended by WDCGG (World Data Center for Greenhouse Gases). The concentration of was increasing continuously by 2.1 ppm/year, while did not show any increasing or decreasing trend clearly for 4 years. The concentration of was slightly increasing and CFCs were decreasing except CFC-12 which has longer lifetime compared with other CFCs. The variations of the greenhouse gases at Gosan were shown to be consistent with the global trend. But the concentration level of in Korea was more or less higher than abroad.

To differentiate temperature effect from the light intensity effect on the formation of secondary products during the photooxidation of toluene--air mixtures, steady-state air temperature was changed from at the same light intensity of in an indoor smog chamber. Smog chamber consisted of 64 blacklights and a reaction bag made of Teflon film. Air temperature was controlled by an air-conditioning system. The starting time for rapid conversion of NO to was slightly delayed with decreasing air temperature. In contrast to light intensity effect, the ozone formation time and the ozone production rate were insensitive to air temperature. Although the formation time for secondary organic aerosols was not changed, the particle number concentration increased with temperature. However, the newly formed secondary organic aerosol mass at lower temperature was higher than that at higher temperature. Since light intensity significantly affected the starting time and quantity of ozone and aerosol formation, it is considered that the temperature could contribute partly the quantity of aerosol formation during the photooxidation of toluene--air mixtures.