Organic fertilizer application reduce ammonia volatilization in an acidic soil

Ammonia (NH3) volatilization has garnered significant concern owing to its detrimental environmental impact. Yet, the specific characteristics of NH3 volatilization and its associated microbial activity in response to various fertilizer management strategies in acidic soils remain poorly understood. To address this gap, we conducted a five-year field observation experiment by applying urea alone, as well as in combination with organic fertilizer (rapeseed cake or Vicia), to explore the effect of soil organic matter (SOM) mineralization on NH3 volatilization and to elucidate the contribution of ammonia oxidizers to NH3 volatilization in the acidic soil. The results revealed that the combined application of organic fertilizers and urea (ranging from 0.63 to 7.81 kg ha- 1) reduced NH3 volatilization compared with applying urea alone (ranging from 2.6 to 13.02 kg ha- 1). Vicia mulching was shown to be more effective in reducing NH3 loss. NH3 volatilization was positively regulated by CO2 emissions. Initially, organic fertilizers applications facilitated SOM mineralization, thereby enhancing NH3 volatilization during the first year. However, after five years of sustained application of these fertilizers, SOM mineralization became suppressed, consequently lowering the cumulative NH3 volatilization. Moreover, NH3 volatilization exhibited a significant negative correlation with the nitrification potential of ammonia-oxidizing bacteria (AOB), which became more abundant after organic fertilizer application. Our results underscore the suppressive effect of organic fertilizer application on NH3 volatilization through the reduction of SOM mineralization. Furthermore, it was elucidated that AOB was the primary drivers of nitrification, regulating the conversion of NH3 to NO3 - in the acidic soil.