Effects Of Ammonium Bicarbonate On Dielectric Relaxation And Dielectric Loss Characteristics Of Soil

Soil nitrogen monitoring has always been one of the key research contents of scholars at home and abroad.Soil nitrogen content monitoring is of great significance to agricultural production and ecological environment.At present,the measurement methods and technologies of soil nitrogen content mainly rely on the instruments in the laboratory,such as continuous flow analyzer or relevant chemical analysis methods.Although the measurement accuracy is high,the speed is slow,and the measurement results have a certain lag,which can not guide irrigation and fertilization in time.Based on the lack of long-term field nitrogen monitoring equipment and related measurement theories,this paper uses dielectric measurement equipment such as vector network analyzer and coaxial probe,and carries out dielectric measurement experiments and research under the coupling condition of soil and ammonium bicarbonate based on the theories of dielectric polarization,dielectric relaxation,dielectric loss and different phase interface double-layer model.In the research process,considering the main factors affecting the dielectric properties of soil,five variables are designed:ammonium ion content N,volume water content θ_v,soil type,test temperature and test frequency.Taking Black soil,Lou soil and Soft soil as objects,soil samples with five different ammonium ion content and five different water content are prepared.The soil dielectric spectrum(1 MHz～4 GHz)are obtained by dielectric measurement.Based on the experimental results and related theories,the dielectric polarization behavior and characteristics of soil coupled with ammonium bicarbonate are analyzed,the dielectric relaxation and dielectric loss characteristics are studied,and the dielectric measurement models of soil water content and soil ammonium nitrogen content are constructed respectively.After research,After research,the following main conclusions are drawn:(1)Under the coupling condition of soil and ammonium bicarbonate,the micro polarization mechanisms affecting the dielectric relaxation and loss characteristics of soil are mainly interface polarization,relaxation polarization and steering polarization in the frequency range below 1 GHz.With the increase of ammonium ion content N and water content θ_v,the relationship between the overall dielectric relaxation and dielectric loss characteristics of soil and frequency is more significant.(2)Under the coupling condition of soil and ammonium bicarbonate,ammonium ions are unevenly distributed in the heterogeneous mixed system,and are densely distributed in the Stern layer close to the surface of soil particles(colloidal particles).With the increase of distance,the concentration of ammonium ions decreases and tends to be evenly distributed.With the increase of ammonium bicarbonate application,the number of ammonium ions increases,more cations are adsorbed into the double electric layer of soil particle interface,and the number of dipole moments in soil increases;On the contrary,with the decrease of ammonium ion content,the number of dipole moments in soil decreases.(3)According to the correlation between the real part of dielectric constantε’and soil volume water contentθ_v,the dielectric measurement model of water content established at the frequency of 146.96 MHz has high correlation coefficient and applicability,and its correlation coefficient R~2 is 0.86854.According to the interaction between the imaginary part of dielectric constantε’and ammonium ion content _NW and the real part of dielectric constantε’,the dielectric measurement model of nitrogen content established at the frequency of 4.00 GHz has high correlation coefficient and applicability,and its correlation coefficient R~2 is 0.89658.(4)Based on Maxwell Garnett theory and formula,combined with Debye relaxation model,a dielectric mixing model is proposed to estimate soil water content.Through comparative analysis with equivalent series model and Bruggeman model,it is determined that the"semi physical semi empirical"water content dielectric measurement model proposed in this paper has high estimation accuracy and applicability.There are still deficiencies in this study:when studying the effects of ammonium ions on the dielectric properties of soil porous media,other salt ions are not considered enough.In the follow-up test and research,it is necessary to contact other salt ions with large content for research and analysis.