Compiling C/N and total-N dataset to support countrywide soil nutrient emission models for Hungary

Soil carbon/nitrogen (C/N) ratios can provide essential information on soil health such as nitrogen limitations for plants or soil microorganisms. Determining soil C/N ratios can be challenging for larger geographic units such as for catchments, as nitrogen heterogeneity depends on several factors like land use, soil types, vegetation cover or seasonality. This paper investigates C/N ratio changes at different levels for diverse land management and land uses at plot-, catchment-, and country scale. For the plot- and catchment scale the study also presents data on seasonal variabilities of C/N ratio. For the countrywide evaluation, a digital soil mapping method was applied. Substantial differences were noted in total nitrogen amounts for arable lands, where the ‘no till’ system had up to 54.7% higher TN compared with ploughing. Catchment based monitoring showed the highest fluctuations for TN in the case of forest soils, while C/N ratios were relatively stable over the course of different seasons for the diverse land uses. Comparison of the topsoil C to N ratios in the European LUCAS and national SIM datasets shows that the difference in expected values is considerable (consecutively 10.35 and 7.41). The discrepancy can be explained partly due to different thematic representativity for land use and partly because of differences in analytical methodology. In addition, samples were taken almost twenty years apart. Overall, our study highlights the significance of land use, land management systems, spatial heterogeneity, time of samples collections, and the inconsistencies between different sampling and measurement methods.