*2.2. Experimental Design*

The field experiment was a balanced 2 × 4 factorial trial conducted on two different sites each year. The first factor was the type of N fertilizer: (i) ammonium nitrate, 34-0-0, (ii) ammonium saltpeter with ammonium sulfur, 32-0-0-5. The second factor was composed of three rates of nitrogen/sulfur plus absolute N/S control. The arrangemen<sup>t</sup> of the 2nd factor was as follows:


The first N or NS rate of 80 kg N ha−1, together with the respective amount of S, was applied before WOSR spring regrowth. The second N rate of 40 or 80 kg ha−<sup>1</sup> was applied at the end of March or the beginning of April. Amounts of applied phosphorus (P) and potassium (K) fertilizers were adjusted to the actual status of P and K soil fertility level, and applied before WOSR sowing. P was used as di-ammonium phosphate (18% N, 46% P2O5), and K as muriate of potash (60% K2O). The size of an individual experimental plot was 400 m<sup>2</sup> (9 × 44.4 m) The fore-crop for WOSR at all sites was winter wheat. Standard tillage technology was applied for soil preparation for WOSR. Immediately after the winter wheat harvest, phosphorus and potassium fertilizers were broadcast on the entire field and shallow stubble ploughing (10–12 cm) + harrowing was done. Two or three weeks later, depending on the planned sowing date, a standard ploughing to a depth of 25 cm was done with simultaneous soil compaction with a Cambell roller. Seedbed preparation and seeding was conducted immediately after ploughing. The amount of seeds, based on 1000 seed weight, was adjusted to reach a plant density at emergence of 40–50 plants m<sup>−</sup>2. The row spacing was 12.5 or 25 cm, depending on the farm equipment. A robust program to control all weeds, pests, and diseases was employed in accordance with standard farm practice during the growing season, following integrated pest managemen<sup>t</sup> (IPM) principles. In order to achieve a homogenous stage of seed maturation (seed moisture of 8%), desiccants were applied. Harvest was performed the earliest seven days later by a combine harvester from an area of 300 m2.



**Table 2.** Main characteristics of meteorological conditions during the study on the background of the long-term averages.

1 January–July; 2 Precipitation; 3 Temperature; 4 Poznan-Ławica Meteorological Station.
