*2.1. Study Area*

This study was carried out with data collected in the 2021 season in 39 wheat (*Triticum aestivum* L.) plots located in the Llanada Alavesa region, situated in the center of the province of Araba/Álava in northern Spain (Figure 1). This region is characterized by agricultural fields growing mainly winter cereals (wheat and barley), potatoes, colza, legumes, forage maize, and sugar beet. Wheat sowing was carried out at a density of 230 kg ha−<sup>1</sup> with Filón variety seeds between 20 and 30 November 2020. All fields were fertilized with chemical fertilizers, averaging 53 kg ha−<sup>1</sup> of N, 36 kg ha−<sup>1</sup> of P, and 102 kg ha−<sup>1</sup> of K in the growth stage (GS) GS21 that corresponds to tillering [58]. For the top-dressing fertilization, 117 kg ha−<sup>1</sup> N was applied in the stem elongation phase (GS30).

According to the Köppen classification, the Llanada Alavesa region has a temperate oceanic climate (Cfb) [59] characterized by an average annual air temperature of 11.7 ◦C. During the summer months, the average temperature reaches 20 ◦C, while the winter months are relatively mild with an average temperature of 6 ◦C. Average annual rainfall was 750 mm, with July and August being the driest months with less than 50 mm of precipitation. The study plots were established over two distinct soil types developed on two different lithologies. Thus, soils on the lithology from the Cretaceous geological era are characterized by steep and irregular terrain, are relatively shallow (20–70 cm), and have a high concentration of calcium carbonate (CaCO3) of over 50%. The dominant soil fraction is silt, which has a concentration exceeding 40%. The second type of soil, sourced from Quaternary material, is deeper (over 120 cm), has a lower concentration of CaCO3 (<25%) and a loamier texture, and the stone content is higher [60].

**Figure 1.** Upper left-hand side of the image shows the general location of the study area within Spain. Upper right-hand side shows detail of the study area with the average yield of each plot (right part). Below, wheat phenological stage and dates when satellite images were acquired. Red squares represent S1 and blue squares represent S2.

The average grain yield of the studied plots (Figure 1) ranged from 4.76 t ha−<sup>1</sup> for the G32 plot to 8.91 for the G7 plot, with an average value for all plots of 7.01 t ha−1. Plot size ranged from 0.72 to 9.42 ha, with 2.46 ha being the average, representing well Llanada Alaves's plot diversity.
