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.