Effect Of Organic Fertilizer And Inorganic Fertilizer Application On N₂O And NO Emissions From Fluvo-aquic Soil In The North China Plain

The North China Plain is an important grain production area in China.Due to the low content of soil organic carbon,farmers have to overuse inorganic nitrogen fertilizer for increasing crop yields.The over-application of nitrogen fertilizer does sustainably increase maize yield at present,and in contrast,it leads to the low use efficiency of nitrogen fertilizer and the increase of N₂O emission.The combined application of organic fertilizer and inorganic fertilizer is widely regarded as a measure to simultaneously increase grain yield and soil organic carbon,however the effect of organic fertilizer and inorganic fertilizer application on N₂O and NO emissions from cropland in the North China Plain is unclear,which may be related to the type and application rate of organic fertilizer.Here,N₂O and NO emission and crop yield in cropland under combined application of different types and rates of organic fertilizers plus inorganic N fertilizer were measured in the North China Plain.Field plot trials under maize-wheat rotation were carried out from June 2018 to May 2019.Eight treatments were designed as follows:no N fertilizer（CK）,inorganic fertilizer（NPK）,40%cow manure N plus 60%inorganic fertilizer N（CM）,40%chicken manure N 60%inorganic fertilizer N（FC）,40%pig manure N plus 60%inorganic fertilizer N（FP）,20%cow manure N plus 80%inorganic fertilizer N（1/2CM）,20%chicken manure N plus 80%inorganic fertilizer N（1/2FC）,and 20%pig manure N plus 80%inorganic fertilizer N（1/2FP）.Soil N₂O fluxes were measured using the static closed chamber method,and other auxiliary variables and crop yields were also monitored.Annual N₂O emission and annual NO emission were 0.70 kg N₂O-N ha^-1 and 0.10kg NO-N ha^-1 under CK,respectively,increased significantly to 2.71 kg N₂O-N ha^-1and 0.32 kg NO-N ha^-11 under NPK.There were no significant differences in N₂O emissions between NPK and CM,FC or FP.However,N₂O emissions were significantly reduced by 30.8%,38.7%and 11.3%,respectively,under 1/2CM,1/2FC and 1/2FP,compared with CM,FC and FP.Decreased input of easily decomposed organic carbon was suggested to reduce the denitrification potential and N₂O emissions.Except for the cow manure treatment in maize season（CM>1/2CM）,NO emissions increased significantly with the decrease of ratio of organic fertilizer to inorganic fertilizer,while the magnitude of increased NO emission was significantly lower than the decreased N₂O emission.There were no significant differences in NO emissions between 1/2CM,1/2FC or 1/2FP and NPK.But N₂O emissions were significantly reduced by 29.5%,38.4%and 21.3%,respectively,under 1/2CM,1/2FC and 1/2FP,compared with NPK.The N₂O fluxes were significantly correlated with soil WFPS during the maize season（P<0.05）.A significant relationship was observed between the N₂O fluxes and soil temperature at a depth of 5 cm in all the treatments during the maize season（P<0.05）.These indicated that soil N₂O flux in maize season was mainly affected by water content,while soil temperature was the key factor affecting N₂O fluxes in wheat season.The cumulative N₂O emissions in wheat season was significantly lower than that in maize season,probably because low temperature delayed urea hydrolysis and reduced nitrification and denitrification.There was a significant linear relationship between N₂O fluxes and soil DOC content during the maize season in all the treatment except CK and NPK treatments（P<0.05）.The results show that organic fertilizer plays a dual role,which not only increased the labile organic carbon and enhanced the soil denitrification potential,but regulated the soil inorganic nitrogen level for the production of N₂O by nitrification and denitrification.Compared with CM,FC,FP and NPK,there was no obvious increase in maize yield under 1/2CM,1/2FC and 1/2FP,while wheat yield was increased.There were no significant differences in maize and wheat yield between 1/2CM,1/2FC and 1/2FP.Therefore,based on the perspective of ensuring crop yield and reducing greenhouse gas emission,the combination application of 25%organic fertilizer nitrogen and 75%inorganic fertilizer nitrogen was a better choice in the North China Plain.