Quantitatively ranking the influencing factors of ammonia volatilization from paddy soils by grey relational entropy

Ammonia (NH₃) volatilization from paddy soils is a main source of atmospheric NH₃ and the magnitude is affected by many factors. Because of the complex field condition, it is difficult to identify the relative importance of individual factor on NH₃ volatilization process in different locations and at different times. In this study, the grey relational entropy method was used to evaluate the relative impact of four main factors (i.e., nitrogen fertilizer application rate, NH₄-N concentration, pH, and temperature of the floodwater) on NH₃ volatilization loss from three different field experiments. The results demonstrated that floodwater NH₄-N concentration was the most important factor governing NH₃ volatilization process. Floodwater pH was the second most important factor, followed by temperature of the floodwater and nitrogen fertilizer application rate. We further validated the grey relational entropy method with NH₃ volatilization loss data from other published study and confirmed the order of importance for the four factors. We hope the findings of this study will be helpful for guiding design to reduce paddy soil NH₃ emission.