The yield potential of switchgrass was verified by testing seven cultivars in a small-scale experiment carried out from 2018 to 2022 on Gleyic Fluvisol under Central European conditions. The treatments are as follows: pre-sowing (i/HA) soil humic preparation Humac AGRO (based on leonardite) with an ameliorative dose of 1000.0 kg ha−1 or (ii/NPK) basic nutrition with a dose of 220.0 kg ha−1 NPK; an annual dose of 70 kg ha−1 N was applied to both treatments (HA, NPK) and compared to (iii/UC) untreated control. A dry matter (DM) yield of 9.02 t ha−1 was achieved in the total average, which varied from 0.05 t ha−1 to 60.64 t ha−1. The yield was affected mainly by years (F-ratio 106.64), then by nutrition (F-ratio 79.03), followed by cultivars (F-ratio 56.87), and finally by replications (F-ratio 0.00). Switchgrass productivity increased according to the utility year; however, the driest year (2020—388 mm, 2021—372 mm, and 2022—288 mm) changed the order of the three full utility years (12.44, 19.13, and 7.73 t ha−1 DM, respectively). HA gives the highest DM yield of 13.69 t ha−1 on average with values of 9.19 and 4.19 for NPK and UC, respectively. The cultivars order was EG 1101 ˃ BO Master ˃ EG 1102 ˃ Kanlow ˃ Alamo ˃ Carthage ˃ NJ Ecotype (21.15, 12.48, 8.14, 7.70, 6.34, 4.47, and 2.89 t ha−1 DM when ranking average yield or 60.64, 45.20, 29.92, 29.15, 17.87, 9.86, and 5.93 t ha−1 DM when ranking maximal yields).

The main objective of the paper was to determine the ligno-cellulose quality and calorific value of switchgrass Panicum virgatum L. The impact of nutrition treatments (pre-sowing soil humic amendment HA and/or NPK, with annual dose of N on both the treatments, and untreated control UC) and years were evaluated as main effects within a pilot experiment with seven cultivars tested during 2018–2022. Two data sets of acid detergent fiber (ADF), acid detergent lignin (ADL), crude cellulose (CE), hemicellulose (HEM), neutral detergent fiber (NDF), and high heating value (HHV) were evaluated, the primary one in terms of quality content and the secondary one in terms of quality yield. The average ADF content of the switchgrass was 43.94% (range 30.15–50.91), while the average contents of ADL, CE, HEM, NDF, and HHV were 9.21% (6.02–12.41), 34.73% (17.98–40.08), 30.49% (21.34–38.41), 74.43% (59.20–81.15%), and 17.206 kJ g−1 (16.579–17.799), respectively. An adequate value of ADF yield was 4.17 Mg ha−1 (0.01–29.31), while for ADL, CE, HEM, NDF and HHV this was 0.79 Mg ha−1 (0.00–5.39), 3.37 Mg ha−1 (0.01–23.92), 2.79 Mg ha−1 (0.01–17.66), 6.96 Mg ha−1 (0.01–46.93), and 1.466 hGJ ha−1 (0.003–10.603), respectively. In terms of the both quality sets the cultivar was confirmed to be the most important factor followed by the year, with nutrition having the least impact. This impact order of the main effects was valid for each of the parameters. Moreover, in terms of quality yield the formation of homogeneity groups corresponded with dry matter yield and therefore with the order of cultivars (EG 1101 ˃ BO Master ˃ EG 1102 ˃ Kanlow ˃ Alamo ˃ Carthage ˃ NJ Ecotype), the years (2021 ˃ 2020 ˃ 2022 ˃ 2019 ˃ 2018), and the treatments (HA ˃ NPK ˃ UC).