Partial organic substitution for chemical fertilizer reduces NO emissions but increases the risk of N loss through nitrification in Tibetan farmland.

The combination of organic fertilizers (OFs) and chemical fertilizers (CF) is a promising agricultural management strategy to improve soil fertility while mitigating NO emissions in croplands. However, there is still lacking of in-depth understanding of the effects of different OF and CF blends on NO emissions and the underlying drivers. To this end, we conducted a short-term soil incubation to address the influences of partial OF substitutions for CF, i.e., 40% substitution of compost (CP), Yak dung (YD), Qingke straw (QS), and sheep dung (SD) on the processes of nitrification and denitrification in sandy loam soils in the Lhasa Valley. We found that CP, QS, and SD reduced cumulative NO emissions by 53.43%, 25.96% and 16.64%, respectively compared to pure chemical fertilizer (N), except YD caused a significant higher in total NO emissions. Fertilization treatments primarily regulate potential NO emissions by affecting denitrification processes. While ammonia-oxidizing archaea (AOA amoA) could be the main driver of nitrification, and nirS abundance explained most of the cumulative NO emissions. In addition, NO-N tends to accumulate in the farmland soils, indicating an increase in the risk of leaching and nutrient loss. Overall, soil NO emission reduction was favored by applying partial organic fertilizer substitution especially after through compost. Co-composting of animal manure and crop residue has more impressive potential for mitigating farmland NO emissions.