Interactive effects of soil moisture, nitrogen fertilizer, and temperature on the kinetic and thermodynamic properties of ammonia emissions from alkaline soil

Abstract

Soil moisture and nitrogen fertilizer application rates are among the key factors affecting ammonia (NH3) emission, particularly in alkaline soil. However, the dynamic and thermodynamic properties of NH3 emissions from alkaline soils have not been extensively studied. In this study, we conducted an incubation experiment and theoretical analysis to investigate NH3 emission dynamics and thermodynamic properties under treatments involving different moisture levels (5%, 15%, 25%, and 35%), nitrogen fertilizer application rates (0, 172.4, and 344.8 mg kg−1), and temperatures (10, 20, 30, and 40 °C). The accumulative NH3 emissions varied significantly among the different moisture, temperature, and nitrogen treatment conditions and exhibited a logarithmic growth trend over time. The highest accumulative NH3 emissions occurred under the following conditions: 344.8 mg kg−1 nitrogen fertilizer, 5% moisture, and 40 °C temperature. The highest average emission rate constant (KN) throughout the entire incubation period was obtained at 40 °C. The KN of NH3 emissions in the high-temperature region (30–40 °C) was more sensitive to temperature. With increasing soil moisture content, the activated free energy (ΔG) initially increased and then decreased. As the nitrogen fertilizer application rate increased, the ΔG decreased, thereby leading to higher NH3 emissions. Combining the kinetic and thermodynamic parameters revealed that temperature, soil moisture, and nitrogen fertilizer application rate were key factors influencing NH3 emissions in alkaline soil, with the nitrogen fertilizer application rate having a greater impact than that of temperature, soil moisture, and their coupling. These findings provide valuable insights into the thermodynamic and kinetic control mechanisms of NH3 emissions, which can be regulated by fertilization and irrigation methods that consider the nitrogen cycle in alkaline soils.