Study On The Kinetic And Thermodynamic Characteristics Of Soil Urea Conversion Under The Coupling Of Water-nitrogen-temperature

At present,China has become the country with the largest nitrogen fertilizer application amount in the world,but the nitrogen utilization efficiency is far lower than the world average.Low nitrogen utilization efficiency can cause not only the waste of resources,but also environmental pollution.Therefore,deeply revealing the mechanism of nitrogen fertilizer transformation is an important prerequisite for solving the bottleneck problem of nitrogen utilization efficiency,and is one of the effective means to solve the environmental pollution fundamentally.The methods of laboratory culture experiment,theoretical analysis and mathematical simulation were adopted in this paper.Kinetic and thermodynamic properties of soil urea conversion were studied under the coupling effects of different moisture contents????60%,80%,and 100%of field capacity?,nitrogen application rates?F??247,309,371,and 433 mg/kg?,and temperatures?T??15°C,20°C,25°C,and 35°C?.The conclusions were as follows:?1?Kinetic characteristics of urea hydrolysis under the coupling of water-nitrogen-temperature was analysed.Results showed that the effects of moisture content,temperature,nitrogen application rate and their interaction on urease activity,hydrolysis rate constant and half-life were as follows:T>F>?>T*F>T*?>F*?>T*?*F.The importance degrees of moisture content,nitrogen amount and temperature to hydrolysis kinetic process were 10.4%,26.8%and 62.8%,respectively.Five models,the water-temperature coupling model K_u??,T?,water-nitrogen coupling model K_u??,F?,temperature-nitrogen coupling model K_u?T,F?and two water-nitrogen-temperature coupling models(K_u-1??,F,T?and K_u-2??,F,T?)were developed.The mean absolute percentage error?MAPE?of the models were 1.89%,2.15%,4.75%,2.89%and 4.01%,respectively.?2?Thermodynamic characteristics of urea hydrolysis under the coupling of water-nitrogen-temperature was analysed.Results showed that the effects of moisture content,nitrogen application rate and their interaction on activation energy were as follows:F>F*?>?.The effects of moisture content,nitrogen application rate,temperature zone(T_zone)and their interaction on temperature coefficient were as follows:T_zone*F>T_zone*F*?>F>?>T_zone>F*?>T_zone*?.The effects of individual factors and their interaction on activation enthalpy??H_u?were as follows:F>?>T>F*?>T*F>T*?>T*F*?,that on activation free energy??G_u?were as follows:T>F>?>T*F>T*?>T*F*?>F*?,that on negative activation entropy?-?S_u?were as follows:T>F>T*F>T*F*?>?>T*?>F*?,and that on activation degree?lgN_u?were as follows:T>F>?>T*F>T*F*?>T*?>F*?.K_u was determined by both?H_u and?S_u.Urea hydrolysis was an endothermic reaction controlled by both enthalpy and entropy.?3?Kinetic characteristics of the ammonium nitrogen conversion under the coupling of water-nitrogen-temperature was analysed.Results showed that the effects of moisture content,temperature,nitrogen application rate,and their interaction on conversion rate constant(K_NH)of ammonium nitrogen were as follows:T>?>T*?>F>T*F>T*?*F>F*?.The importance degree of moisture content,nitrogen amount,and temperature to the conversion process of ammonium nitrogen were 39.1%,8.3%,and 52.6%,respectively.Four models,the water-temperature coupling model K_NH??,T?,water-nitrogen coupling model K_NH??,F?,temperature-nitrogen coupling model K_NH?T,F?,and water-nitrogen-temperature coupling model K_NH??,F,T?were developed.The MAPE values of the models were 3.5%,1.3%,4.3%,and 3.44%,respectively.?4?Thermodynamic characteristics of the ammonium nitrogen conversion under the coupling of water-nitrogen-temperature was analysed.Results showed that the effects of moisture content,nitrogen application rate,and their interaction on activation energy of the ammonium nitrogen conversion were as follows:F*?>F>?.The effects of moisture content,nitrogen application rate,temperature zone(T_zone)and their interaction on temperature coefficient of the ammonium nitrogen conversion were as follows:T_zone>T_zone*F*?>?>T_zone*F>F*?>T_zone*?>F.The effect of individual factors and their interaction on activation enthalpy(?H_NH)were as follows:T*F*?>?>F*?>T*F>F>T*?>T,that on activation free energy(?G_NH)were as follows:T*F*?>T>T*F>F*?>T*?>F>?,that on activation entropy(?S_NH)were as follows:T>T*?>T*F*?>F*?=F>T*F>?,and that on activation degree(lgN_NH)were as follows:T>?>T*F*?>T*?>F>T*F>F*?.K_NH was determined by both?H_NH and?S_NH.The ammonium nitrogen conversion was an endothermic reaction controlled by enthalpy and entropy.?5?Kinetic characteristics of ammonia volatilization under the coupling of water-nitrogen-temperature was analysed.Results showed that the effects of moisture content,temperature,nitrogen application rate,and their interaction on ammonia volatilization rate constant?K_N?were as follows:T>F>?>T*F>T*?>F*?>T*?*F.The importance degree of moisture content,nitrogen amount,and temperature to the ammonia volatilization process were 12.2%,17.9%,and 69.9%,respectively.Four models,the water-temperature coupling model K_N??,T?,water-nitrogen coupling model K_N??,F?,temperature-nitrogen coupling model K_N?T,F?,and water-nitrogen-temperature coupling model K_N??,F,T?were developed.The MAPE values of the models were 3.5%,1.3%,4.3%,and 3.44%,respectively.?6?Thermodynamic characteristics of ammonia volatilization under the coupling of water-nitrogen-temperature was analysed.Results showed that the effects of moisture content,nitrogen application rate,and their interaction on activation energy were as follows:?>F*?>F.The effects of moisture content,nitrogen application rate,temperature zone and their interaction on temperature coefficient were as follows:F>F*?>T_zone*?>T_zone*F*?>T_zone*F>?>T_zone.The effect of individual factors and their interaction on activation enthalpy??H_N?were as follows:T*F*?>T*F>?>F>F*?>T>T*?,that on activation free energy??G_N?were as follows:F>T*F*?>T*F>F*?>T*?>T>?,that on negative activation entropy?-?S_N?were as follows:T>T*F*?>T*F>T*?>F*?>F>?,and that on activation degree?lgN_N?were as follows:T>F*?>?>T*F*?>T*F>T*?>F.K_N was determined by both?H_N and?S_N.Ammonia volatilization was an endothermic reaction controlled by both enthalpy and entropy.?7?Kinetic characteristics of nitrification under the coupling of water-nitrogen-temperature was analysed.Results showed that the effects of moisture content,temperature,nitrogen application rate,and their interaction on nitrification rate constant(K_NO)were as follows:T>?>T*?>F>T*F>F*?>T*?*F.The importance degree of moisture content,nitrogen amount,and temperature to the nitrification process were 3.5%,17.9%,and 51.9%,respectively.Four models,the water-temperature coupling model K_NO??,T?,water-nitrogen coupling model K_NO??,F?,temperature-nitrogen coupling model K_NO?T,F?,and water-nitrogen-temperature coupling model K_NO??,F,T?were developed.The MAPE values of the models were 3.49%,3.81%,3.02%,and2.57%,respectively.?8?Thermodynamic characteristics of nitrification under the coupling of water-nitrogen-temperature was analysed.Results showed that the effects of moisture content,nitrogen application rate,and their interaction on activation energy of nitrification were as follows:F>F*?>?.The effects of moisture content,nitrogen application rate,temperature zone and their interaction on temperature coefficient of nitrification were as follows:T_zone>T_zone*?>T_zone*F>F>T_zone*F*?>?>F*?.The effect of individual factors and their interaction on activation enthalpy(?H_NO)were as follows:T*F*?>T*F>F>T>F*?>?>T*,that on activation free energy(?G_NO)were as follows:?>T*F*?>T*?>F*?>T*F>T>F,that on the negative value of activation entropy(-?S_NO)were as follows:?>T*F>T*F*?>F*?>T*?>T>F,and that on activation degree(lg N_NO)were as follows:?>T*F*?>F*?>T*F>F>T*?>T.K_NO was determined by both?H_NO and?S_NO.Nitrification was an endothermic reaction controlled by both enthalpy and entropy.?9?Based on the analysis of the kinetic and thermodynamic characteristics of urea conservation,a new urea conversion prediction model?MCA-F-ANN?combined with modified cluster method and full feed-forward neural network was developed.T,W,F,reaction time,p H,and electrical conductivity?Ec?were regarded as inputs,and NH₄⁺–N,NO₃^-–N,and NH₃ contents were regarded as outputs.When MCA-F-ANN model was adopted to predict nitrogen content,the MAPE of NH₄⁺–N,NO₃^-–N,and NH₃ contents was 3.180%,2.756%,and 3.656%,respectively.This model had high simulation accuracy.