E static chamber (uC); and dc/dt is the line slope of the gas concentration change over time.Tillage Conversion on CH4 and N2O EmissionsTable 2. Correlation analysis between changes in CH4 and N2O with soil temperature and soil moisture per sampling time.Sampling time Soil temperature CH4 N2OSoil moisture CH4 N2OR2008.10.18 2008.11.08 2008.12.16 2009.01.12 2009.02.27 2009.03.06 2009.03.20 2009.04.22 2009.05.19 0.6020* 0.6180* 0.7314** 0.6490** 0.6597** 0.3824 0.2876 0.4476* 0.8870**n3 3 3 3 3 3 3 3R0.3832 0.0377 0.0087 0.0723 0.3053 0.1461 0.0257 0.3044 0.n3 3 3 3 3 3 3 3R0.5429* 0.2945 0.0085 0.2988 0.5370* 0.0417 0.4966* 0.5154* 0.4593*n3 3 3 3 3 3 3 3R0.1020 0.1241 0.5142* 0.5200* 0.0914 0.0005 0.6132* 0.6735** 0.5027*n3 3 3 3 3 3 3 3*P,0.05, **P,0.01. doi:10.1371/INCB039110 journal.pone.0051206.tGWP of CH4 and N2OThe global warming potentials (GWP) were determined by measuring CH4 and N2O emissions. The GWP of CH4 and N2O are 25 and 298 times higher, respectively, than that of CO2 (the GWP of CO2 is 1) [27] and are calculated as follows: GWP H4 TF H4 25GWP 2 OTF 2 O 298where GWP(CH4) is the GWP of CH4 (kg CO2 ha21); TF(CH4) is the total uptake of CH4 (kg CO2 ha21 a21); 25 is the GWP coefficient of CH4; 100 is the time scale of climate change (a); GWP(N2O) is the GWP of N2O (kg CO2 ha21); TF(N2O) is the total emission of N2O (kg CO2 ha21 a21); and 298 is the GWP coefficient of N2O.Soil Factor MeasurementsThe meteorological data during the experiment were obtained from an agricultural weather station 1662274 in the experimental area. To evaluate the relation between soil temperature and moisture and CH4 and N2O emissions, we measured soil temperature at a depth of 5 cm and the soil moisture in the 0?0 cm soil layers simultaneously using a soil temperature, moisture and electric conductivity instrument (WET brand, made in the UK) as the temperature and moisture data collection tool. The soil samples were collected using a soil sampler with five replicates in each different tillage treatment and were dried and triturated after mixing. This sample was used to determine the SOC, NH4+-N and pH using the Potassium Dichromate Heating Method, the UV Colorimetric Method and the Potentiometry Method, respectively [28].Figure 3. A Linear regression between the CH4 uptake fluxes and SOC, B Linear regression between the CH4 uptake fluxes and soil pH. Arrows indicate the regression equation between the CH4 uptake fluxes and soil organic carbon, soil 1662274 in the experimental area. To evaluate the relation between soil temperature and moisture and CH4 and N2O emissions, we measured soil temperature at a depth of 5 cm and the soil moisture in the 0?0 cm soil layers simultaneously using a soil temperature, moisture and electric conductivity instrument (WET brand, made in the UK) as the temperature and moisture data collection tool. The soil samples were collected using a soil sampler with five replicates in each different tillage treatment and were dried and triturated after mixing. This sample was used to determine the SOC, NH4+-N and pH using the Potassium Dichromate Heating Method, the UV Colorimetric Method and the Potentiometry Method, respectively [28].Figure 3. A Linear regression between the CH4 uptake fluxes and SOC, B Linear regression between the CH4 uptake fluxes and soil pH. Arrows indicate the regression equation between the CH4 uptake fluxes and soil organic carbon, soil 1516647 pH. *indicates P,0.05. doi:10.1371/journal.pone.0051206.gGrain YieldThe grain yield of winter wheat was sampled from the 1.5 m6 6 m portion in the central area of each plot.Tillage Conversion on CH4 and N2O EmissionsFigure 4. A Linear regression between the N2O emission fluxes and soil NH4+-N, B Linear regression between the N2O emission fluxes and soil pH. Arrows indicate the regression equation between the N2O emission fluxes and soil NH4+-N, soil pH. **indicates P,0.01. doi:10.1371/journal.pone.0051206.gStatistical AnalysesThe data were analyzed using analyses of variance and the SPSS 17.0 Statistical Analysis System and were mapped using Sigma Plot 10.0. The mean standard deviation and least significant difference were calculated for comparison of the treatment means.Results CH4 and N2ODifferences in CH4 flux were observed when converting from HT to HTS, from RT to RTS and from NT to NTS (Figs. 2 A toC). The soil absorption of CH4 increased in different periods after conversion to subsoiling compared with the con.
