Effect And Driving Mechanism Of Adding Organic Fertilizer On N₂O Emissons And Isotopic Signature From Vegetable Soil

As one of the three major greenhouse gases,N₂O has received extensive attention.Farmland ecosystems are main source of N₂O emissions,and fertilization will increase N₂O emissions in agricultural soil further.The agronomic measures of vegetable fields are characterized by high water and high fertilizer,and the N₂O problem is also the most prominent.In recent years,the state has vigorously advocated the partial replacement of inorganic fertilizer with organic fertilizer,and the specific effect of organic fertilizer on N₂O production is not clear.It is urgent to carry out relevant work to solve these proplems.In this study,our purpose were to study the mechanism of nitrogen transformation under the action of soil microorganisms.Furthermore,defining the microbial driving mechanism of soil N₂O emissions can provide a theoretical basis for N₂O reduction in farmland and develop reasonable fertilization measures.The specific conclusions of the test were as follows:Effect of different proportions of manure on N₂O emission behavior.Test consisted of two parts,field and indoor?without acetylene and with acetylene?.The treatment included 100%sheep manure,80%sheep manure+20%inorganic fertilizer,50%sheep manure+50%inorganic fertilizer,100%inorganic fertilizer and no fertilizer control.The results showed that the N₂O emissions and cabbage yield of sheep manure were significantly lower than that of inorganic fertilizer under the same nitrogen application rates;N₂O emissions of the 100%inorganic fertilizer was the highest in all treatments,but the cabbage yield was not significantly higher for the 100%inorganic fertilizer than 50%inorganic fertilizer+50%organic fertilizer treatment in the field experiment;50%sheep manure+50%inorganic fertilizer treatment has the highest N₂O emission in indoor culture.The N₂O isotopocule mapping(?¹⁵N^bulk-SP)showed that the denitrifier and nitrifier denitrification processes of sheep manure;while the inorganic fertilizer contributed the same proportion of four microbial activities.In addition,indoor test with the addition of acetylene showed that N₂O reduction and nitrification were not completely inhibited.Effects of different proportions of commercial organic fertilizers on N₂O emission behaviors.Test consisted of a field static gas box test and an undisturbed soil column box?without acetylene and with acetylene?test.The treatment included 100%commercial organic fertilizer,80%commercial organic fertilizer+20%inorganic fertilizer,50%commercial organic fertilizer+50%inorganic fertilizer,100%inorganic fertilizer and no fertilizer control.The results showed that there was no significant difference in N₂O emissions,ammonium nitrogen and nitrate nitrogen concentration,and cabbage yield under the same nitrogen application rates.The?¹⁵N^bulk and?¹⁸O of N₂O were the highest in organic fertilizer and decreased with the decrease of organic fertilizer ratio,and the trend of SP value was opposite.The N₂O isotopocule mapping showed that nitrifier nitrification and fungal denitrification and denitrifier denitrification occurred in the static gas box.Nitrifier nitrification and denitrifier bacteria denitrification mainly occurred in the undisturbed soil column box.100%commercial organic fertilizer and 80%commercial organic fertilizer had higher denitrification,while urea and 50%commercial organic fertilizer had higher nitrification.Effects of different types of organic and inorganic fertilizers on N₂O emission behavior.There were 5 treatments in the 2016 test and 7 treatments in the 2017 test.The results showed that under the same nitrogen application conditions,N₂O emissions and cabbage yield of the three inorganic fertilizers including urea,potassium nitrate and diammonium phosphate were significantly higher than that of the three organic fertilizers including sheep manure,cow manure and chicken manure.However,the application of inorganic fertilizer to soil leads to soil acidification.?¹⁵N^bulk,?¹⁸O and SP values were higher in the organic fertilizer than the inorganic fertilizer,except for the higher?¹⁸O value in potassium nitrate.The N₂O isotopocule mapping showed that inorganic fertilizer promoted more nitrification,while organic fertilizer promoted denitrification.In addition,potassium nitrate mainly enhanced fungal denitrification.Fungal denitrification also played an important role in other treatments.The effect of N₂O reduction on the isotopomer ratios for organic fertilizer.Three kinds of organic fertilizers including chicken manure,cow manure and sheep manure were set under anaerobic conditions?pure He?.The results showed that the three organic fertilizers had no significant effect on soil OM?organic matter?,pH and C/N.The N₂O emission caused by denitrification was mainly related to the nitrate content in soil.The results of stable isotope method and acetylene method showed that the reduction extent of N₂O of three organic fertilizers was about 80.7%and 76.6%,respectively.The?¹⁸O,?¹⁵N and SP of N₂O of different fertilizers were not significantly different.In addition,the N₂O reduction increased the?¹⁸O and SP values,and?(¹⁸O)_R and SP_R under the complete N₂O reductions were–20‰and–5.8‰,respectively.The SP_R differed from direct observations by 3‰.