The Effects Of Nitrogen Levels And Nitrification Inhibitors On Nitrous Oxide Emissions In An Intensively Managed Vegetable Cropping System

Recently,China's vegetable planting acreage increased year by year.With the characteristics of the high level of water and fertilizer inputs,vegetable field has become an important source of the overall agricultural greenhouse gas emissions?GHGs?.Nitrogen?N?fertilizer is an important factor contributing to the N₂O emissions,thus the relationship between N₂O emissions and different N levels of particular ecosystems could better predict N₂O emissions from the region and specific locations under different nitrogen application rates.Application of nitrification inhibitors can improve crop yields and NUE,reduce environmental pollution.Thus it is necessary to carry out research in studying the effect and mechanism of application of different nitrification inhibitors in vegetable ecosystem.Biological nitrification inhibitor with respect to chemical nitrification inhibitors has many advantages and it is worth exploring.Therefore,We used the field experiments and indoor incubation experiments in this study,which is divided into the following four sections:?1?To identify quantitative relationships between different application rates of nitrogen and N₂O emissions and calculate the emission factor applied to the soil vegetable greenhouse gas emissions,while determine the optimal amount of nitrogen fertilizer to provide a scientific basis for the effective control of N₂O emissions for vegetable production in reasonable nitrogen application technology.we conducted a two-year round field experiment by using static chamber-gas chromatographic techniques in a continuously cultivated vegetable cropping system,including four experimental treatments:NO?blank treatment,without fertilization?;N1?1/3 of local conventional nitrogen fertilizer?;N₂?2/3 of nitrogen Fertilizer local conventional?;N3?local conventional nitrogen fertilizer?and N4?4/3 of local conventionalnitrogen fertilizer?.?2?To evaluate the effects of different chemical nitrification inhibitors on N₂O emissions,vegetabl yields and NUE,a 2-yr field experiment with four treatments(without fertilizer?CK?,regular urea?Urea?,urea + dicyandiamide?DCD?,urea + nitrapyrin?CP?performed in triplicate was carried out in an intensive vegetable field using the static chamber and gas chromatography method.?3?To evaluate the effects of biological nitrification inhibitors on N₂O emissions,vegetabl yields and NUE,a 2-yr field experiment with four treatments?without fertilizer?CK?,regular urea?Urea?,urea + dicyandiamide?DCD?,urea + nitrapyrin?CP?performed in triplicate was carried out in an intensive vegetable field using the static chamber and gas chromatography method.?4?The effects ofdifferent nitrification inhibitors in situ field trails on soil pH,total nitrogen,soil microbialnitrogen immobilization,nitrification and denitrification process were studied,which can provide a theoretical basis scientific and rational application of these inhibitors in order for the long-term.The main findings are as follows:1.N application significantly affected the N₂O emissions.The cumulative N₂O emissions amounted to 33.8±3.8,50.4±4.4,60.0±3.9,73.4±3.0 and 96.2±5.4 kg.N ha-1 for the five N application rates,respectively;An exponential relationship was observed between cumulative N₂O emissions and N application rates,which suggested that application of N fertilizer increased the risk of N₂O emissions of vegetable land.Seasonal changes significantly affect the cumulative N₂O emissions and emission factors.Specially,the lowest yield scaled N₂O emissions was observed in the N₂ treatment.In addition,N₂ treatment significantly increased plant yield and NUE compared with N3 treatment.Thus,the recommended application of fertilizer in vegetable land would be N₂ treatment.Theaveraged N₂O emission factor of four treatments is 2.0%?range 1.8-2.3%?,which is twofold than that in IPCC?1.0%?.2.Compared with the conventional fertilization treatment,the CP treatmentignificantly reducing N₂O emissions by 15.3 kg N ha-1?,improved vegetable yield andnitrogen use efficiency by 12.6%and 17.6%,respectively.The nitrification inhibitor DCDhave obvious nitrification inhibitory in indoor incubation experiment,but not significantlyaffect N₂O emission,vegetable yield and nitrogen use efficiency in the field trials.3.Compared with the conventional fertilization treatment,the BNI treatmentignificantly reducing N₂O emissions by 18.7 kg N ha-1,improved vegetable yield andnitrogen use efficiency by 6.7%and 11.6%,respectively,which has a continuous effect in the field.4.The CP and BNI treatments can significantly increase soil pH,increase microbial biomass nitrogen content,reducing the apparent nitrification rate of the soil.And the changes in CP urea and biological nitrification inhibitor treatments were more evident.Therefore,this study indicated that high levels of nitrogen fertilizer increased risk of N₂O emissions.The relationship between N₂O emissions and nitrogen fertilizer was exponential growth.The optimal recommended nitrogen fertilizer rate is to reduce the 1/3 of local conventionnal fertilizer rate,which could significantly reduce N₂O emissions,improve yield and NUE;while the effects of application of new chemical and biological nitrification inhibitor?CP and BNI?in increasing vegetable yield and reducing N₂O emissions were superior to DCD,and they are worthy of further applications research.