*2.1. Experimental Conditions*

The field trials were conducted on hop farms located in Bragança (41◦4133.6 N, 6◦4432.7 W, and 850 m above sea level), north-eastern Portugal, from 2016 to 2018. The region benefits from a Mediterranean-type climate, with an average annual temperature and precipitation of 12.7 ◦C and 772.8 mm, respectively [25]. Data on average monthly temperatures and precipitation during the experimental period are shown in Figure 1.

**Figure 1.** Average monthly temperature and precipitation during the three years of the study.

Six plots, named here as Plot 1 (~0.5 ha), Plot 2 (~0.5 ha), Plot 3 (~4 ha), Plot 4 (~2 ha), Plot 5 (~2 ha) and Plot 6 (~2 ha), were used in this experimental protocol. The classification of the fields was made with the farmers' help and was based on the crop growth and yield in the previous years. In Plot 1, the plants were classified as weak vigour plants, as the hop bines did not reach 4 m in height. In Plot 2, the growth of the plants was classified as fair, as the plants did not reach the top of the pole (7 m). In Plot 3, the vigour of the plants was classified as good, as the hop bines exceeded 7 m in height, but the volume of the canopies, aboveground biomass and cone production were clearly below optimal. In the Plots 4, 5 and 6, the vigour of plants was classified as very good vigour, since the hop bines reached a full size and produced abundantly.

Before the installation of the trials, all the plots were analysed for soil properties. The soil samples were collected in three replicates at 0–0.20 m depth. Each replicate was a composite sample, prepared from soil collected from 15 random points. The samples were oven-dried at 40 ◦C and sieved in a mesh of 2 mm. Thereafter, they were analysed for pHH2O (soil: solution, 1:2.5), cation-exchange capacity (ammonium acetate, pH 7.0), organic C (wet digestion, Walkley–Black method), extractable P and K (Egner–Riehm method) and soil separates [26]. The results of the soil analysis are presented in Table 1.


**Table 1.** Selected soil properties (average ± standard deviation; *n* = 3) determined just before the start of the experiments from soil samples collected in plots of different plant vigour (weak, fair, good and very good) at 0–0.20 m depth.

a Pipette method; b Potentiometry; c Walkley–Black; d Egner–Riehm; e Ammonium acetate, pH 7.

All the plots where the experiments took place were grown on a high trellis system supported by concrete poles and a network of steel cables placed at a height of 7 m. The hop bines were guided from the ground to the upper net with nylon threads. At planting, the seedlings were spaced at 2.8 m × 1.6 m between and within rows. Two tutors emerged from each original place where the seedlings were planted, giving rise to a density of 2232 plants per hectare, which were trained in Spring into two twin canopies.

The plots were irrigated by flooding the space between rows. Farmers estimate the average use of 6000 m<sup>3</sup> of water per hectare and per year, equivalent to 600 mm. From the end of May to mid-August they perform an average of 10 watering events of 60 mm each.

The floor was managed by tillage (3 to 4 passes per year), which has a double function of controlling weeds and removing the superficial crust caused by this irrigation method allowing a better water infiltration at subsequent irrigation events.

All the plots received an annual fertilization plan consisting of the application of a compound NPK (7:14:14) fertilizer late in winter (just before plant regrowth from winter resting period) at a rate of ~500 kg ha−1. Thereafter, during the growing season, two side dress N applications were performed by using ~200 kg ha−<sup>1</sup> of ammonium nitrate (27% N) (applied when plants were close to reach the top wire) followed by ~450 kg ha−<sup>1</sup> of calcium nitrate (15.5% N) (applied at early flowering).
