Interactions of fertilisation and crop productivity on soil nitrogen cycle microbiome and gas emissions

Abstract. Fertilised soils are a significant source of nitrous oxide (N₂O), a highly active greenhouse gas and stratospheric ozone depleter. Nitrogen (N) fertilisers, while boosting crop yield, also lead to N₂O into the atmosphere, impacting global warming. We investigated relationships between mineral N fertilisation rates and additional manure amendment with different crop types through the analysis of abundances of N cycle functional genes, soil N₂O and N₂ emissions, nitrogen use efficiency (NUE), soil physicochemical analysis and biomass production. Our study indicates that N₂O emissions are predominantly dependent on the mineral N fertilisation rate and enhance with increased mineral N fertilisation rate. Higher N₂O emissions were attained with the application of manure. Manure amendment also increased the number of N cycle genes that are significant in the change of N₂O. Contrary to our hypothesis, there was no significant influence of crop type on soil N₂O emissions. The study indicated dominance of nitrification over denitrification in the soil. Microbial analyses also showed the potential role of comammox and DNRA processes as a source of N₂O. Our study did not find soil moisture to be significantly linked to N₂O emissions. Results of the study provide evidence that for wheat, a fertilisation rate of 80 kg N ha⁻¹ is closest to the optimal rate for balancing biomass yield, N₂O emissions, and achieving high NUE. Sorghum showed potential for cultivation in temperate climate, as sorghum maintained low N₂O emissions and N losses on mineral N fertilisation rate of 80 kg N ha⁻¹.