| Methane?CH4?is one of the most important greenhouse gases after CO2,and the main sources of CH4 emissions come from various agricultural activities.Among all kinds of agricultural sources,paddy field is one of the most important sources of CH4.It is important to mitigate CH4 emission from the perspective of farmland management.Therefore,in the present study we investigated the effect of altering rice-flooded-fallow paddy?RF?to rice-wheat rotation?RW?on the emissions of CH4 in Sichuan hilly region.The results were as follows:1.RF and RW showed obvious seasonal patterns in CH4 fluxes: high in autumn and summer season,while low in spring and winter season.After altering winter-flooded paddy to rice-wheat rotation,the cumulative emissions of CH4 reduced by 43%.The reduction of cumulative CH4 emission in rice season accounted for 39% of the total reduction,and accounted for 61% during the non-rice season.At the same time,we got wheat output.Therefore,altering RF to RW could significantly reduce the CH4 emission,and the CH4 emission in the non-rice season was greater than that in the rice season and increased crop yields.2.When the wheat was planted after the water was drained in fallow season of RF,the CH4 emissions in wheat season were reduced by 70% to 81% compared to those in RF.Therefore,altering RF to RW could significantly reduce the CH4 emission in fallow season.Moreover,from 2012 to 2015,CH4 average fluxes in fallow season of RF were about 3 to 80 times higher than those in wheat season of RW,and the cumulative emissions were about 3 to 6 times higher.The CH4 fluxes from RF were significantly higher than those from RW.Average CH4 fluxes during the three non-rice seasons from2012 to 2015 in RF were 0.8,1.62 and 3.65 mg C m-2h-1,and the fluxes in RW were 0.01,0.1 and 1.05 mg C m-2h-1.CH4 emission during non-rice seasons in RF and RW increased over years.3.After altering RF to RW,CH4 fluxes in rice season of RW reduced by 24% to 33%compared to those in rice season of RF.Therefore,altering RF to RW not only could significantly reduce the CH4 emission in fallow season,but also in rice season.Duringrice season from 2013 to 2014,the CH4 average fluxes from RF were 2 times higher than those in RW,and the cumulative fluxes were 1.4 times higher.The CH4 fluxes from RF were significantly higher than those from RW.During the rice season from 2013 to 2014,CH4 average fluxes from RF were 10.22 and 11.78 mg C m-2 h-1,and the fluxes from RW were 5.64 and 6.89 mg C m-2 h-1.During the two years,CH4 fluxes from RF and RW increased over years in rice season.4.In rice season of RF,there was no significant difference on CH4 fluxes between usual nitrogen use and no nitrogen fertilizer in 2013?p>0.05?.However,the CH4 flux of usual nitrogen use was significantly higher than that of no nitrogen fertilizer.And there was a significant different between them?p<0.05?.During the fallow season of RF from2014 to 2015,the CH4 flux of usual nitrogen use was significantly higher than that of no nitrogen fertilizer.As a whole,nitrogen fertilizer reflected promotion on CH4 emission of RF.From 2012 to 2015,the cumulative CH4 emission in RW with usual nitrogen use were2.3,1.7 and 1 times than those in wheat season with no nitrogen fertilizer,respectively.And the CH4 cumulative fluxes of UN in RW during rice season were about 1.1 and 1.3times higher than NN.So the CH4 fluxes of UN in RW whether in rice season or wheat season.Nitrogen fertilizer reflected promotion on CH4 emission of RW.5.From 2012 to 2015,CH4 fluxes in rice season of RW and RF with plants were higher than no plant treatments,and there was a significant different between them?p<0.05?.In rice season in 2013 and 2014,CH4 cumulative fluxes from RF with plants were about 2.2 and 3.1 times higher than those of no plant,and CH4 cumulative fluxes from RW with plants were about 2.7 and 1.8 times higher than those with no plant.However,the CH4 fluxes with plants in wheat season of RW had little difference with those of no plant.As a whole,plant reflected significant promotion on CH4 fluxes in rice season of RW and RF,but there was no significant influence on CH4 fluxes in wheat season.6.CH4 fluxes from RF and RW were significantly positive correlated with the soil temperature at the 5cm depth?p<0.05?;when the soil temperature was higher than 10?from RF,and higher 15? from RW,the CH4 fluxes increased with the increase of soil temperature.The sensitivity of soil to temperature from RW was lower than RF.Aftercomprehensive analysis of environmental factors which affecting CH4 emissions,we know that ammonium nitrogen,nitrate nitrogen,dissolved total nitrogen and soil temperature had significant influence on CH4 flux from RW,and the soil temperature was the major factor;but in the fallow season of RF,field water depth was the major factor on CH4 emission.7.There was no significant relationship between soil moisture and CH4 flux from RW?p>0.05?,and field water depth was significant positive correlation with CH4 flux from RF?p<0.05?,mainly concentrated in 1 to 5 cm water layer.Also,there was no significant relationship between soil organic carbon and CH4 flux from RF?p>0.05?.There was no significant relationship between the content of ammonium nitrogen,nitrate nitrogen,dissolved total nitrogen and the CH4 flux?p>0.05?,and the relationship between soil organic carbon and CH4 flux from RW was not significant?p>0.05?,it's same as the relationship between ammonium nitrogen,dissolved total nitrogen and CH4 flux?p>0.05?,there was a significant negative correlation between nitrate nitrogen content and CH4 flux?p<0.01?.Overall,during altering winter-flooded paddy to rice-wheat rotation,the change of soil moisture condition and temperature and dissolved total nitrogen are the major factor on CH4 emission,and altering winter-flooded paddy to rice-wheat rotation can reduce CH4 fluxes while increasing crop yields.Therefore,altering winter-flooded paddy to rice-wheat rotation is beneficial to environment and farmers. |
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