*2.3. Experimental Design*

The objective of the experiment was to quantify the "baseline" mineralization of soil organic N, since the N mass balance used in this experiment included N mineralization not only from this compartment, but also from other compartments, including animal waste and annual crop or grassland residues recently incorporated into the soil. To this end, (i) the 137 experimental fields were cropped with silage maize for four (since 2011) or five (since 2010) consecutive years without any mineral or organic fertilization, and (ii) only mineralization data for 2012, 2013 and 2014 were considered, to exclude N flows resulting from inputs of fertilizers and crop residues incorporated into the soil before the experiment began. The experimental design was, thus, based on estimating N mineralization for three consecutive years. Experimental monitoring was performed on an area of 1485 m<sup>2</sup> (33 m × 45 m), divided into three subplots of 45 m2 (6.0 m × 7.5 m) in the middle for replicate measurements.
