太湖地区典型轮作与休耕方式对稻田水稻季N_(2)O和CH_(4)排放量的影响

Effects of Typical Crop Rotation Systems and Land Fallow on Paddy Soil N_(2)O and CH_(4) Emissions in Taihu Lake Region of China

轮作休耕是实现"藏粮于地、藏粮于技"的重要途径之一,目前在太湖稻田区域主要推广紫云英(Astragalus sinicus L.)-水稻(Oryza sativa L.)、油菜(Brassica napus L.)-水稻和休耕-水稻典型轮作与休耕方式。在太湖地区典型稻田水稻生长季设置了6个处理:(1)紫云英-水稻轮作,不施N肥处理,MRN0;(2)紫云英-水稻轮作,当地常规施肥量(300 kg·hm^(-2),以纯氮计,下同),MRN300;(3)油菜-水稻轮作,不施N肥处理,RRN0;(4)油菜-水稻轮作,当地常规施肥量(300 kg·hm^(-2)),RRN300;(5)休耕-水稻轮作,不施N肥处理,FRN0;(6)休耕-水稻轮作,当地常规施肥量(300 kg·hm^(-2)),FRN300。通过田间试验,研究了不同轮作与休耕方式对水稻产量、氮肥利用率及稻田温室气体CH_(4)和N_(2)O排放的影响,从而为综合评价轮作休耕方式提供科学依据。田间试验结果显示,与不施氮肥处理相比,在不同轮作休耕方式下施氮300 kg·hm^(-2),可增加53.7%—60.0%的水稻产量,以MRN300处理水稻产量最高,与RRN300和FRN300处理相比,水稻产量分别提高了1.6%和6.0%。在不施氮水平下,MRN0、RRN0和FRN0各轮作处理间N_(2)O排放通量和累积排放量均值差异不显著(P>0.05)。而在施氮300 kg·hm^(-2)下,紫云英-水稻轮作可降低N_(2)O排放通量和累积排放量,与RRN300和FRN300处理相比,N_(2)O排放通量分别降低了36.0%(P<0.05)和2.1%(P>0.05)。在同一施氮水平下,紫云英-水稻轮作CH_(4)排放通量和累积排放量最小,与RRN300和FRN300处理相比,MRN300处理CH_(4)排放通量分别降低了1.1%和6.7%,CH_(4)和N_(2)O的全球增温潜势(GWP)分别降低了3.3%和6.5%,单位水稻产量温室气体排放强度(GHGI)分别降低了4.6%和11.6%。综上,紫云英-水稻轮作对提高水稻产量,降低温室气体排放效果最好。

Optimizing crop rotation system together with adopting land fallow management is one of the important strategies to realize the goal of“hiding grain in the land and grain in technology”.Currently,milk vetch(Astragalus sinicus L.)-rice(Oryza sativa L.)rotation,rape(Brassica napus L.)-rice rotation and fallow-rice rotation are the dominated rice-cropping systems in Taihu Lake region of China.In this study,we conducted a field experiment and evaluated the responses of rice yield,nitrogen use efficiency(NUE)and CH4 and N_(2)O emissions during rice-growing season to the abovementioned different rice-cropping systems.Our study included six treatments:(1)milk vetch-rice rotation with no N-fertilizer addition(MRN0);(2)milk vetch-rice rotation with 300 kg·hm^(−2) N application(MRN300);(3)rape-rice rotation with no N-fertilizer application(RRN0);(4)rape-rice rotation with 300 kg·hm^(−2) N application(RRN300);(5)fallow-rice rotation with no N-fertilizer application(FRN0);and(6)fallow-rice rotation with 300 kg·hm^(−2) N application(FRN300).Compared with no N-fertilizer application treatments,we found that rice yields were increased by 53.7%‒60.0%with 300 kg·hm^(−2) N application in different rice-cropping systems.MRN300 treatment had the highest rice yield,which was 1.6%and 6.0%higher than that in RRN300 and FRN300 treatments,respectively.No significant difference was observed among different ricecropping systems under no N-fertilizer application(P>0.05).However,milk vetch-rice rotation(MRN300)could decrease N_(2)O cumulative N_(2)O emissions by 36.0%(P<0.05)and 2.1%(P>0.05)as compared to rape-rice(RRN300)and fallow-rice(FRN300)cropping systems,respectively,under the N application of 300 kg·hm^(−2) N.MRN300 had the lowest cumulative CH4 emissions,which was 1.1%and 2.1%smaller than that in RRN300 and FRN300,respectively.Overall,compared to the other rice-cropping systems,milk vetch-rice rotation(MRN300)decreased the GWP 3.3%‒6.5%and the GHGI 4.6%‒11.6%,respectively.Our results suggest that the implementation of milk vetch-rice rotation is effective in improving rice yield and reducing greenhouse gas emissions.