KINETICS AND THERMODYNAMICS OF SOIL NITRIFICATION UNDER THE COUPLING OF MOISTURE CONTENT AND TEMPERATURE

Soil temperature and moisture content play critical roles in controlling nitrogen (N) cycling. This study aimed to determine the effect of temperature, moisture content, and the interaction between the two on the kinetic and thermodynamic parameters and reveal the key thermodynamic control mechanism of ammonia volatilization. Laboratory culture experiment was conducted under different temperatures (15 degrees C, 25 degrees C, and 35 degrees C) and moisture contents (60%, 80%, and 100% field capacities), and the NO3--N content was measured every two days. Results showed that the increasing moisture content and temperature would increase the activation degree (lgN) and the percentage of activated molecules. This result promoted the effective collision frequency between the molecules, increased the probability of achieving the transition state (vertical bar Delta S vertical bar), and decreased the energy consumption (Delta G) or the energy consumption per temperature (Delta G/T) during the realization of transition state. These conditions increased the amount and accumulation rate (K) of NO3--N. The interaction of temperature and moisture content showed no significant effect on the kinetic parameters and thermodynamic parameters. Since Delta H > 0, Delta G > 0, and Delta S < 0, the accumulation process of NO3--N was an endothermic reaction controlled by enthalpy. The results supplemented the control mechanism of NO3--N accumulation fertilized with urea.