Gridded Soil Surface Nitrogen Surplus on Agricultural Land: Impact of Land Use Maps

Nitrogen (N) compounds as plant nutrients play a key role in food production. Additional N nutrients, including mineral fertilizers, have been applied to agricultural land to an extent that impacts on the global N cycle (1). Negative consequences become visible to the local and global environment through eutrophication, acidification and through the formation of N2O, a powerful greenhouse gas. Gridded maps of N surplus on cropland have been developed to display major N flows on several levels (global and local) and are key for the development of policies to manage the globally increased N input (2,3). Grasslands, which are responsible for around half of the total agricultural N2O emissions, have not been analyzed in greater detail yet although required as a background of N management policies (4,5). A major obstacle here is the limited availability of data on grassland N fixation as well as removal at harvest. Here we analyze available input information for sensitivities and uncertainties, with the aim of developing scientific support for N management policies. The concept reflects a similar approach for cropland (6),
where we tested the influence of different crop maps. In this work we tested the impact of different land use maps in assessing N surplus on agricultural land (arable land and permanent pastures) for the year 2010. This way we are able to identify critical regions to minimize environmental impacts while also offering a first analysis of the sensitivity of the results, in order to indicate areas where further research is needed.