Spatial-heterogeneous granulation of organic amendments and chemical fertilizer stimulated NO emissions from agricultural soil: An microcosm study.

The promising application modes of organic fertilizer (OF) and chemical nitrogen (N) fertilizer (CF) could be the homogeneous granulation (HG: OF and CF are distributed spatially evenly) and spatial heterogeneous granulation (SG: OF and CF are distributed separately in space), where the N transformation processes, such as the nitrous oxide (NO) emissions, are greatly influenced by the spatial distribution of the OF and CF, particularly. Currently, there is a lack of in-depth understanding about the microbial mechanisms of the SG and HG application on NO emissions, and the related functional guilds (ammonia oxidizers and heterotrophic denitrifiers) respond to the granular fertilizer is yet not known. In the present study, we made CF (N-(NH)SO), cow compost and maize straw (2% or 8% based on the N proportion) into granular of 1 cm in diameter, in HG and SG forms, respectively, and then applied these granules in soils for 80 days incubation. Results showed that, compared with HG treatments, the SG treatment promoted the ammonium (NH), nitrate (NO) and microbial biomass carbon (MBC) intensities, and increased the NO emissions possibly through ammonia oxidize bacteria dependent nitrification and fungal denitrification. In addition, the high maize residues proportion in organic fertilizer significantly mitigated NO emissions by the coupled impacts of suppressed nitrification and enhanced denitrification enzyme activity with high C input. Overall, our results suggest that spatial heterogeneous granulation of and CF may induce higher risk of NO emissions and the higher proportion of maize residues could potentially mitigate such increased emissions.