Study Of Nitrous Oxide And Nitric Oxide Fluxes From The Vegetable Field In Dongting Lake Area

As a key part in cropland ecosystem,vegetable field with the characteristics of "high multiple crop index and large amount of fertilizer" is an important source of nitrogen-containing gases(N2O and NO).N2O and NO are not only greenhouse gases that directly or indirectly cause global warming,but also polluting gases that cause ozone holes.They play an important role in global climate change and ecological environment.Therefore,it is of great significance to study the N2O and NO emissions from vegetable fields.The study was carried out in the Dongting lake area open-air fertilized vegetable field.Using static chamber-gas chromatography technique and static chamber-chemiluminescence methods to observe in-situ N2O and NO emissions from rows and inter-rows in traditional vegetable lands under the conventional management mode during near one year(two vegetable seasons).The findings are as follows:Dongting lake area vegetable field is an important emission source of atmospheric N2O and NO.Under the local conventional fertilization management model(fertilizing amount 521 kg N ha-1 yr-1),N2O fluxes from rows and inter-rows in vegetable fields were-1.1 to 3285.6 ?g N m-2 h-1 and-1.1 to 530.8 ?g N m-2 h-1 respectively.There was a significant difference between rows and inter-rows(P<0.01).According to the proportion of area occupied by rows and inter-rows(7:3),the calculated weighted mean value is 3.9?2369.4 ?g N m-2 h-1.NO fluxes from rows and inter-rows were-0.9 to 1291.9 ?g N m-2h-1 and-0.3 to 309.5 ?g N m-2h-1,with the weighted mean value being-0.8?997.2?g N m-2h-1.The annual cumulative emission fluxes of N2O and NO were 9.43 kg N ha-1 and 1.41 kg N ha-1 respectively.The direct emission coefficient of N2O and NO were 0.74%and 0.24%respectively.The emission fluxes of N2O and NO from open-air vegetable fields in subtropical regions were characterized by high emissions during spring and summer,and low emissions during autumn and winter,which is due to the combined effect of environmental factors and management measures,such as soil temperature,soil moisture content(WFPS),fertilization,and rotational tillage.The exponential relationships between N2O or NO fluxes and temperature were found under different time periods.N2O emissions have a direct relationship with soil moisture.However,there were different relationships between N2O fluxes and WFPS under different WFPS ranges.There was a significant positive correlation when WFPS<60%,and a significant negative correlation when WFPS>60%.This study did not find that soil moisture had a significant effect on NO emissions.Fertilization enhanced N2O and NO emissions;N2O and NO continued to emit highly for a period of time after fertilization.The trends of N2O and NO emissions were basically consistent with the trends of soil NO3-and NH4+ concentrations,but there was only significant linear correlation between NO emissions and soil NH4+concentrations,which indicates N2O and NO emissions are regulated by other factors.In the vegetable fields,the total errors of annual cumulative N2O and NO fluxes were 3%and 2%respectively.The systematic error of N2O emissions caused by the flux calculation method made the estimated flux low 0-42%,and the error of NO flux due to the calculation method cannot be estimated.Random error was mainly from the observation space of the flux differences.When conducting greenhouse gas flux observation in farmland,space repeat should be increased appropriately to reduce the random error.At the same time,attention should also be paid to areas with significant differences such as ridges and ridges,and observation points should be laid out to avoid systematic deviations in flux observations.