Danish agriculture is highly subsidized and regulated. There is, therefore, a large amount of data documenting agricultural practices. These data sets are primarily managed by the Ministry of Food, Agriculture and Fisheries of Denmark They expose the data both for download and as wfs/wms. One of the key data sets is the fields data set (Marker) the data sets include information on the crop of the individual field for each year since 2008. A idea of the amount of fertiliser used in a given area can be calculated by combining this data with the annual allowed amount of fertilizer for a given crop and soil type combination. The amount of allowed fertiliser is available in “Bekendtgørelse om jordbrugets anvendelse af gødning i planperioden” apendix 1 The data for season 2021/2022 is, for instance, available here