*2.2. Soil and Plant Sampling*

Within each of the fields, sampling points of soil and plants were georeferenced using a Global Positioning System (GPS) receiver. The locations of the sampling points were selected to obtain large variability in the studied traits, i.e., soil properties as well grain yield and ear number (Figure 3). The characteristics of each of the three research sites are presented in Table 1.

Soil samples were collected from a layer of 0–90 cm at the end of winter or in early spring before the starting of the vegetation. Grain yield and number of ears per square meter were determined at the full maturity of plants in plots of 2 m<sup>2</sup> (2 × 1 m<sup>2</sup> subplots, each located very closely to the soil and plant sampling points). The following statistical parameters were calculated: average, standard deviation, minimum, and maximum for each field in a given year.

**Figure 3.** Normalized Difference Vegetation Index (NDVI) maps of the experimental fields in three locations ((**<sup>a</sup>**,**b**): Bro˙zówka—A, (**<sup>c</sup>**,**d**): Zdziechów—B, and (**<sup>e</sup>**,**f**): Kryłów—C) in two seasons: 2017 (on the left) and 2018 (on the right), from dates when maximum average value of this index was achieved, with soil and plant sampling points superimposed. Explanation of color representation of NDVI values and the dates of NDVI acquisition are given.
