The effect of fertilisation and crops on nitrogen sequestration based on microbial analysis and N2O emissions
Authors: Kuusemets Laura 
Published: February 2023

EGU General Assembly 202323-28 April 2023&#160;THE EFFECT OF FERTILISATION AND CROPS ON NITROGEN SEQUESTRATION BASED ON MICROBIAL ANALYSIS AND N2O EMISSIONSLaura Kuusemets1, &#220;lo Mander1, Jordi Escuer Gatius2, Alar Astover 2, Mikk Espenberg11 University of Tartu, Institute of Ecology and Earth Sciences, Vanemuise 46, 51014 Tartu, Estonia2 Estonian University of Life Sciences, Institute of Agricultural and Environmental Sciences, Kreutzwaldi 5, 51014 Tartu, EstoniaContact: laura.kuusemets@ut.ee&#160;Nitrogen (N) is an essential nutrient in crop production as N is used to make amino acids (make the proteins that construct cells), is one of the building blocks for DNA, and is a significant component of chlorophyll (photosynthesis). The input of N in the form of fertilisers increases crop yield. On the other hand, agricultural nitrogen inputs can cause N leaching and the loss of biologically active N to the atmosphere, contributing to global warming. Thus, excessive and inefficient use of N fertiliser results in enhanced crop production costs and pollution of water bodies and the atmosphere. Agricultural landscapes are an important source of nitrous oxide (N2O), a highly active greenhouse gas and stratospheric ozone depleter. The main objectives of the study were to evaluate whether and how different crop species and fertilisation norms affect nitrous oxide (N2O) emissions and soil microbiome using the closed chamber method and quantitative polymerase chain reaction (qPCR) analysis.The study was done in the IOSDV (International Organic Nitrogen Long-term Fertilisation Experiment) experimental field located in the southern part of Estonia. The crop species studied were barley (cultivar &#8220;Elmeri&#8221;), sorgo (cultivar &#8220;Susu&#8221;), and wheat (cultivar &#8220;Mistral&#8221;). The fertiliser treatment is constituted of mineral nitrogen fertilisation and fertilisation with farmyard manure. Three nitrogen fertiliser treatment rates were used: 0, 80 and 160 kg ha&#8722;1. Samples were collected over seven months, from April 2022 to October 2022. qPCR was used to quantify the abundance of bacteria- and archaea-specific 16S rRNA, nitrification (bacterial, archaeal and comammox (complete ammonia oxidation) amoA) denitrification (nirK, nirS, nosZI and nosZII) and dissimilatory nitrate reduction to ammonium (DNRA; nrfA gene) marker genes from the soil samples.The results of this study indicate that different fertilisation influence N2O emissions and the highest N2O emissions are emitted from the highest N fertilizer treatment (160 kg ha&#8722;1). On average, sorgo fields fertilised with farmyard manure had slightly higher N2O emissions compared to fertilisation with mineral fertiliser.&#160;In addition, on average, the highest and smallest N2O emissions occurred with wheat and barley, respectively. The N2O emissions among all crop species decreased during drought in the summer. The preliminary microbial analysis shows that nitrification was the primary process resulting in N2O emissions, but the different groups of nitrifiers showed different trends under different fertilisation and crops.&#160;