*2.2. Weather Conditions*

Weather conditions during the growing seasons (2016–2018) are presented using the hydrothermal index, according to Sielianinov [19] (Figure 1). Variability in weather conditions during the study was reflected in the index values. Low index values (multi-year average) were recorded in March 2016 and 2017, April 2016, 2017 and 2018, May 2016 and 2018, June and July 2018, August 2018 and September 2016 and 2018. More favourable moisture conditions during the growing season were observed in 2016 and 2017, compared to the much drier 2018 growing season (May: K = 0.43, June: K = 0.41).


**Table 3.** Soil characterization at the study site.

**Figure 1.** Sielianinov index (K) during the growing seasons 2016–2018 (recorded at the Agrometeorological Observatory in Gorzy ´n, Poland). Sielianinov K Index: <0.5—drought, 0.5–1.0—semi-drought, 1.0–1.5—zone of optimal moisture, >1.5—excessive moisture.2.3. Influence of Fertilizers on Nitrogenase Activity (Diazotrophy).

At the commencement of the flowering phase, the level of diazotrophy (as expressed by nitrogenase activity) was measured with the acetylene-ethylene reduction (ARA) method [20]. Five plants were randomly selected from the experimental treatment plots and were placed into tightly sealed 2000 mL vials. To achieve a 10% (*v*/*v*) acetylene concentration in the gas phase (air), purified acetylene (C2H4) was then injected into each vial. After one hour, 1 mL of gas was withdrawn and stored in small glass vials (each vial sealed with a rubber septum and aluminum seal). Ethylene concentration was quantified using a gas chromatograph CHROM 5 (Laboratorni Pˇristroje, Praha, Czech Republic). Dinitrogenase activity was quantified as the amount of acetylene reduced to ethylene (expressed as nMC2H4 plant−<sup>1</sup> <sup>h</sup>−1) and is presented here as the average value of five replications (from each measurement).

#### *2.3. Soil Sampling for Biochemical Analysis*

The soil samples that were collected from the upper 0–20 cm layer were used for biochemical analyzes. During the study period, the samples were collected at four terms during each growing season: 1st term—plant emergence (BBCH 5–10), 2nd term—full plant growth (BBCH 35–40), 3rd term—plant inflorescence (BBCH 51–59), 4th term—after harvest.

Soil samples were collected from 5 locations in each experimental plot (in four replications for each of the nine treatments). In total, 36 soil samples (weight per sample: 1 kg) were collected.
