The Production And Adsorption Mechanism Of Biochar Based Nitrogen Fertilizer And Its Evaluation Of Agricultural Applications

In order to increase the yield of greenhouse vegetables,there is a widespread phenomenon of excessive nitrogen fertilizer application.As a well-performing absorbent soil amendment,biochar has shown its application prospects in slow-releaseing of nutrient elements and reducing soil nitrogen loss.At present,most of the research on biochar-based nitrogen fertilizers is about its slow-release effect and biochar-based nitrogen fertilizers on crop growth.The research on the relationship between the preparation process of biochar-based nitrogen fertilizers and the effects of soil-crop systems is still insufficient.In this study,peanut shells were used as raw materials,oxidative modification methods were used to improve the adsorption capacity of biochar.The related physical and chemical properties of oxidized modified boichar were determined through characterization analysis.The adsorption system for inorganic nitrogen was constructed and the adsorption mechanism was explored through thermodynamic and dynamic fitting.Based on the results,nitrogen-carrying biochar with high adsorption performance were produced for further experiments.Nitrogen-carrying biochar were used as the carbon-based nitrogen fertilizer,which were compared with conventional mixed application method of biochar and nitrogen fertilizer,the ecological significance of combined application of biochar and nitrogen fertilizer in soil-crop system through soil column and cultivation experiments.The contents of this experiment include the following aspects:1.Preparation and physicochemical properties analysis of modified biochar:modified biochar suitable for mass production was prepared by soaking in different acids.The results of characterization analysis showed that acid washing could reduce the ash content of the biochar surface from 32.45 wt.%to 6.83 wt.%and decrease pH from 9.6 to 7.1.Experiment results demonstrated that the modification treatment of biochar in this experiment mainly plays the role of smoothing the surface of biochar and enhancing the hydrophilicity and surface electron exchange capacity of biochar.Acid treatment will cause certain pore collapse and damage.Hydrogen peroxide,as a weakly acidic oxidant,can enhance the structural stability of biochar while removing ash.2.Analysis of the adsorption mechanism of oxidized modified biochar on nitrate nitrogen and ammonium nitrogen in aqueous solution.The results show that the adsorption of nitrate nitrogen by biochar depends on the pH of the adsorption system,NO₃^--N show positive adsorption on the surface of biochar only when the adsorbent is acidic.The hydrogen peroxide-modified biochar showed a good adsorption capacity for NO₃^--N and the maximum adsorption rate could reach 40%when the pH of aqueous solution was equal to 2.Under acidic conditions,the adsorption of nitrate nitrogen by the modified biochar in this experiment was based on chemical adsorption.Acid treatment can greatly enhance the adsorption capacity of NH₄⁺-N in aqueous solution.Hydrogen peroxide-modified biochar showed the highest adsorption capacity of NH₄⁺-N among the five biochars(123.23 mg·g^-1).According to the results of the adsorption isotherm and the kinetic model fitting,the adsorption of ammonium nitrogen by modified biochar in this experiment is mainly related to the oxygen-containing functional groups on the surface of the biochar.The increase of NH₄⁺-N adsorption capacity is mainly related to the chemical adsorption process of biochar and the particle diffusion phenomenon that occurs in the porous structure of biochar.Through the research on the adsorption performance of biochar on nitrate nitrogen and ammonium nitrogen,the modified biochar which prepared in this experiment is more suitable for the improvement of slightly alkaline soil because of its weak acidity.The poor adsorption capacity of nitrate nitrogen under neutral or alkaline conditions makes it unsuitable for loading nitrate nitrogen as carbon-based nitrogen fertilizer.Ammonium nitrogen showed strong adsorption capacity,which made hydrogen peroxide-modified biochar more suitable for nitrogen loaded carbon-based biochar fertilizer production.3.Research on the effect of different combined application mode of biochar and nitrogen fertilizer on soil nitrogen loss:a maximum adsorption system were consracted based on the results of adsorption experiments,and nitrogen-loaded biochar were prepared as a biochar-based nitrogen fertilizer（CN）.The inhibition and control effects of soil nitrogen under different combined biochar and nitrogen fertilizer application methods were study compared with conventional mixed combined application of biochar and nitrogen fertilizer（C+N）,single application of biochar（C）,and single application of nitrogen fertilizer（N）.Its main conclusions are as follows:1)Compared with C+N,CN can significantly increase the available nitrogen content in soil and reduce soil nitrogen leaching.Under the same nitrogen fertilizer gradient,the leaching amount of nitrate nitrogen of CN is only 75%of C+N,which is 50%of N.Although the nitrogen loading mode can reduced the leaching of ammonium nitrogen to a certain extent,the result was not significant.2)The amount of ammonia volatilized in the soil treated with CN is less than that of C+N and less than N.Therefore,the carbon-based nitrogen fertilizer is made by adsorption of biochar and nitrogen fertilizer,can effectively reduce the loss of inorganic nitrogen in the soil compared with the traditional mixed method.3)Soil N₂O emission was inhibited by single application of biochar.In the same nitrogen fertilizer application gradient,the soil N₂O emission of CN is significantly smaller than that of C+N.The main reason is that the nitrogen-loading biochar adsorbed together with nitrogen fertilizer before it is applied to the soil,and the slow-release effect of nitrogen fertilizer in the soil is better than that of mixed application.4)The single application of biochar to the soil of the facility vegetable field can significantly increase the aboveground biomass of pakchoi.The larger the amount of biochar added,has a certain inhibitory effect on the aboveground and underground biomass.Compared with C+N treatment,CN can significantly increase the biomass,root surface area and root volume of pakchoi,and improve the soil nitrogen absorption rate,apparent utilization rate and partial nitrogen fertilizer productivity of the facility vegetable field.4.Effects of different biochar and nitrogen fertilizer application methods on soil greenhouse gas emissions and microbial community structure:1)Soil CO₂ emissions are mainly related to the amount of biochar added.The C/N ratio of the soil is related to the aeration of the soil.The results shows that under the same nitrogen application and the same biochar addition gradient,the accumulation of C+N carbon dioxide emissions is greater than that of CN,meanwhile the C/N of the soil treated with CN is less than C+N.It is indicated that the application nitrogen-loaded of biochar can reduce soil CO₂ emissions to a certain extent.2)The emission of soil CH₄ is mainly related to the permeability of the soil and the available carbon source.The mixed application of biochar and nitrogen fertilizer can significantly increase the emission of soil CH4.During the cultivation process,the soil treated with C,N and C+N Both CH₄ are discharged in a positive direction,while the cumulative emission of CH₄ treated by CN is negative.It is indicated that nitrogen-loaded biochar inhibited soil CH₄ emission at the initial stage of application.3)The addition of biochar is conducive to the metabolism of amino sugars in the soil.The application of nitrogen loaded biochar（CN）is more conducive to the stability of the soil microbial community than the mixed application of biochar and nitrogen fertilizer（C+N）.