Study On Greenhouse Gases Emissions And Soil Carbon Budget In Maizeand Rice Ratation Field

A field experiment was conducted at the Huaqiao town in Hubei Province from 2013 to 2014, in order to investigate the effects of different maize/rice cropping systems on greenhouse gases(GHG) emissions and soil carbon budget. In this experiment, five treatments were designed, including early rice-autumn maize(RM), spring maize-autumn maize(DM), spring maize-late rice( traditional transplanting)(MR1), spring maize-late rice(cup seedling transplanting(MR2),and early rice-late rice(DR). In situ observations were conducted on seasonal dynamics of CH4、N2O、CO2 emissions by static chamber-gas chromatography; GWP and GHGI of different cropping patterns were evaluated; soil carbon pool characteristics of different cropping patterns were analyzed; net soil carbon budget(NSCB) and the rate of change in soil organic carbon under different cropping patterns( δ SOC) were estimated. The main results were summarized as the following:(1) Different cropping systems had significant effects on CH4 emissions(P<0.05). CH4 cumulative emissions for each cropping pattern ranged from 3.21±0.39 g/m2(DM) to 179.9±7.97g/m2(DR). CH4 emissions mainly occurred in the rice season, and the emissions of late rice was higher than early rice. The CH4 emission of maize season was low. The CH4 cumulative emissions of maize season accounted for 9.8%~20.2% of total emissions. Compared with DR, other cropping systems significantly reduced CH4 by 83.1% ~97.0%. The CH4 emissions of DM was significantly lower than other treatments(P<0.05).(2) Different cropping systems had significant effects on N2 O emissions(P<0.05). N2 O cumulative emissions for each cultivation pattern ranged from 0.73±0.06g/m2(DR)~19.16±0.37g/m2(DM). N2 O emissions were mainly concentrated in the maize season, and the emissions in autumn maize was higher than spring maize. The dynamics of N2 O fluxes turned out to be similar in maize season. The N2 O emissions flux was low in rice season, N2 O cumulative emissions of rice season accounted for 2.0%~15.5% to total N2 O emissions. The N2 O cumulative emission of RM was significantly higher than MR1 and MR2. The N2 O emissions of DM is significantly higher than other cropping systems(P<0.05).(3) Different planting patterns had significant effects on CO2 emissions(P<0.05). CO2 cumulative emissions for each cultivation pattern ranged from 1262±260g/m2(DR)~4285±13.1g/m2(DM)。CO2 mainly emitted in maize season, and the emissions of autumn maize was higher than spring maize. The dynamics of CO2 fluxes turned out to be similar in maize field. CO2 emissions of rice season was significantly lower than the maize season, CO2 cumulative emissions of rice season accounted for 3.9%~32.1% in maize-rice cropping patterns. Compared with RM pattern, MR1 and MR2 significantly enhanced the CO2 emissions reached by 9%~21%. CO2 emission of DM was significantly higher than other cropping systems.(4) GWPs were significantly different among the cropping systems(P<0.05). The greenhouse effect caused by CH4 emission had the maximum contribution to GWP of DR, reached to 53.3%~72.9%. N2 O and CO2 emissions had great contribution to GWP of other maize/rice systems. N2 O contribution was 20.3%~57.3%, while CO2 contribution was 40.7%~69.9% to GWP. GWP of DM was significantly higher than other systems. Compared with DM, other patterns significantly reduced GHGI(P<0.05).(5)Net soil carbon budget(NSCN) estimates showed that: maize season showed net carbon output while the rice season exhibited net carbon input. DR showed a net carbon input, while, DM and MR2 showed net carbon output. The carbon output of DM were greater than MR2 significantly(P<0.05). Compared with the DR, maize-rice rotation significantly reduced soil carbon input, reduced the δSOC and promoted the carbon emissions. Compared with DR, maize-rice rotation significantly promoted soil carbon emissions.In total, compared with the double cropping of rice, maize-rice rotation reduced emissions of CH4, increased emissions of N2 O and CO2, but the GWP was not significantly reduced. The double cropping of maize significantly increased emissions of N2 O and CO2, enhanced the GWP; The maize season showed soil carbon output while the rice season showed net carbon input. Compared with the double cropping of rice, maize-rice rotation promoted the soil carbon output but had the higher yield.