| In recent years, global warming and organic pollution have been paid much attention as two most important environmental problems. Farmland ecosystem is an important source of greenhouse gases emission. Herbicides, as an important part of field managements, inevitably influence greenhouse gases emission from soil by affecting the crop and the activity and community of soil microorganism.The objectives of this research were:1) to examine the effect of different typical herbicides and fertilizers application on greenhouse gases emission from rice-winter wheat rotation system, and further2) to explore the possible affected mechanism of N2O emission, and hence the result would be helpful to exactly estimate or mitigate farmland greenhouse gases and properly utilize herbicides. To approach the above objectives, indoor simulation incubaion experiment and field experiment in situ were employed in this study. Laboratory simulation experiment was carried out to study the effects of6typical dryland herbicides (atrazine, paraquat, glyphosate, tribenuron-methyl, acetochlor and fenoxaprop-P-ethyl) on soil respiration and N2O emissions from soil added with nitrogen fertilizers (NH4)2SO4or urea under the condition of30%(g/g) soil moisture and to study the effects of2typical flooded herbicides (butachlor and bensulfuron-methyl) with urea application on soil respiration, CH4and N2O emissions from soil under55%(g/g) simulated soil moisture. The rice field experiment dealt with the effects of the herbicides butachlor and bensulfuron-methyl on soil-plant respiration, CH4and N2O emissions in a dry direct seeded rice field and the possible mechanism of N2O emission affected by butachlor and bensulfuron-methyl application by measuring NH4+-N and NO3-N contents of the soil and the number of nitrifying and denitrifying bacteria. The wheat field experiment was carried out to study the effects of three typical wheat herbicides acetochlor, bensulfuron methyl and fenoxaprop-P-ethyl on soil-plant respiration and N2O emission.Indoor simulation incubation results showed, the effects of different herbicides on soil respiration and N2O emission were different under the same incubation condition and the effects of the same herbicide on soil respiration and N2O emission from soil added with different nitrogen fertilizers were also different. With the soil moisture of30%and urea amendment, tribenuron-methyl significantly enhanced soil respiration and N2O emission (P <0.05), and its soil respiration and N2O emission were1.26and1.53times higher than those from the control, respectively. Parquat significantly increased N2O emission with the increase of49%(P<0.05) and had no obvious influence on soil respiration (P>0.05). With (NH4)2SO4application, glyphosate inhibited soil respiration significantly by38.7%(P <0.05) and had no significant influence on N2O emission (P>0.05). Acetochlor significantly increased N2O emissions with the increase of53%(P<0.05) and had no obvious influence on soil respiration (P>0.05). Atrazine and fenoxaprop-p-ethyl had no significant influence on soil respiration and N2O emission from soil added with the two kind of nitrogen fertilizers (P>0.05). With the soil moisture of55%and urea amendment, butachlor enhanced soil respiration and N2O emission significantly (P<0.05), and its soil respiration and N2O emission were1.06and1.30times higher than those from the control, respectively. Bensulfuron-methyl had no obvious influence on soil respiration and N2O emission from soil (P>0.05). Butachlor and bensulfuron-methyl had no significant influence on CH4emission from soil (P>0.05).Field results indicated, butachlor enhanced soil-rice system’s respiration rate at the first week during rice growing season and then inhibited respiration rate. Finally, it had no obvious influence on respiration rate at the end of the rice growth period. Bensulfuron-methyl significantly inhibited respiration rate before base fertilizers application. After that, it had no obvious influence on respiration rate. After the first herbicides application, butachlor and bensulfuron-methyl promoted CH4emission from soil significantly (P<0.05). And then after the second herbicides application, butachlor and bensulfuron-methyl inhibited CH4emission (P<0.05). Over the whole rice growth period, butachlor application significantly increased N2O emission with the increase of77%(P<0.05). Bensulfuron-methyl had no obvious influence on N2O emission (P>0.05), but the mean of N2O cumulative emissions for bensulfuron-methyl treatment was higher than that from CK. N2O emission affected by butachlor was due to the increased NH4+-N and NO3-N contents of the soil. The increased NH4+-N contents and reduced NO3-N contents of the soil leaded to the result that bensulfuron-methyl had no obvious influence on N2O emissions. In the present study with the average WFPS (68.6%), nitrification was responsible for N2O production in a dry direct seeded rice field and the nitrifying bacteria plays an important role in N2O emission. The wheat field experiment showed, there were no significant differences on the dynamic pattern of respiration and N2O emission among the three herbicides acetochlor, tribenuron-methyl and fenoxaprop-p-ethyl treatments. However, the three herbicides significantly inhibited respiration rate in the middle wheat growth period. Acetochlor inhibited N2O emission significantly by31.5%(P<0.05). Tribenuron-methyl and fenoxaprop-p-ethyl had no significantly difference on N2O emission (P>0.05). |
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