Agricultural nitrogen input data
Estimated average total annual application of manufactured nitrogen (1km
resolution, kg/km2/year) was extracted for England
from the raster CEH Land Cover® plus Fertilisers (CEH, Wallingford, UK;
https://www.ceh.ac.uk). CEH dataset used data from Defra British
Survey of Fertiliser practice (2010-2015) to derive average annual
application of manufactured fertilisers for each crop type and then
derived total application at 1km resolution using crop areas from CEH
Land Cover® plus: Crops (averaged 2015-2017) (Osório et al.2019). As changes in land use intensity in the UK were limited, with
trends stable overall since 1994 (Martay et al. 2018), we assume
that values based on these maps are representative for the sampling
years (2011 and 2012).
For the Netherlands, mean values of nitrogen fertilizer application rate
by crop were extracted from the database of the Netherlands Enterprise
Agency (RVO) for 2016 (Gewascodelijst Stikstofgebruiksnormen ;
https://english.rvo.nl). To estimate the mean value of nitrogen applied
as fertilizer at 1km resolution (in kg/km2/year), we
calculated a weighted average, taking into account the proportion of
each crop in the landscape. Crop coverage per site were extracted for
each 1km2 cell as an average of the BRP
(Basisregistratie gewaspercelen ) shapefiles 2015 and 2016
obtained from the RVO (https://english.rvo.nl/).
\begin{equation}
N\_Fer=\sum{(Proportion\ of\ each\ crop\ category\ \times\ mean\ annual\ application\ rate\ for\ the\ category)}\nonumber \\
\end{equation}These years (2015-2016) correspond to the median of study years in the
Netherlands included in the analyses, that are 2013, 2014, 2017 and
2018.