The environmental trade-off of fertiliser, residue and catch crop management in Danish cropping systems

Context: Nitrogen is an essential macronutrient in agriculture, affecting both crop yields and soil health. In
Denmark, one of the most densely farmed regions in the world, excess reactive nitrogen (Nr) compounds are lost
to the environment along gaseous and hydrological pathways in forms such as nitrate, ammonia, nitrogen oxides
and dinitrogen.
Objectives: Here, we aim to assess the effect of different field management practices (fertilisation, crop residue
management or cultivation of catch crops) on environmental Nr losses and the field scale soil net GHG balance (i.
e., sum of soil C stock changes and direct and indirect N2O emissions).
Methods: For this purpose, highly detailed data from the Danish Agricultural Watershed Monitoring Program
(LOOP-program; 2013–2019) were used in combination with the process-based model LandscapeDNDC.
Results and conclusions: The results indicate that a mixture of organic and synthetic fertilisers turns soils to a
stronger net sink of GHGs (~70 – ~514 kgCO$_2$ eq ha$^{-1}$ yr$^{-1}$) compared to exclusive use of only one type of
fertiliser. In addition, incorporating crop residue and cultivation of catch crops increases the nitrogen use effi-
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ciency (NUE) by 3–11 % on average and decreases environmental Nr losses.