Industrial Hemp Finola Variety Photosynthetic, Morphometric, Biomechanical, and Yield Responses to K Fertilization Across Different Growth Stages

The growing interest in Cannabis&nbsp:sativa as a highly used crop is present worldwide. There are limited data about the effect of potassium (K) fertilizer on industrial hemp yield for dual purposes (seed and stem production). The current study aimed to investigate the influence of adding two different K fertilizers, KCl and K2SO4, at two growth stages (flowering and ripening) on the productivity and chlorophyll a fluorescence (ChlF) of Cannabis sativa, variety Finola. Before sowing, different K treatments were applied: K1&mdash:100 kg ha&minus:1 KCl (60% K) and K2&mdash:100 kg ha&minus:1 K2SO4 (52% K, S 17%). The OJIP (O stands for &ldquo:origin&rdquo: (minimal fluorescence), P for &ldquo:peak&rdquo: (maximum fluorescence), and J and I for inflection points between the O and P levels) data were recorded and used for ChlF transients and individual ChlF parameters during vegetation. At harvest, the stem morphology parameters and yield (plant height, stem weight and diameter, and stem and seed yield), tensile strength, and the modulus of elasticity were determined. The results show the sensitivity of minimal (F0) and maximal fluorescence (Fm), electron transport from QA to intersystem electron acceptors (ET0/(TR0 &minus: ET0)), and electron transport flux until PSI acceptors (RE0/RC) to K fertilization. The parameters that described electron transport (ET0/RC, &psi:E0, and &phi:E0), performance index on absorption basis (PIABS, TR0/DI0, and &phi:P0), dissipation (DI0/RC), and electron transport to photosystem I (&phi:R0 and &delta:R0/(1 &minus: &delta:R0)) had a reaction only at the growth stage, indicating a change in their activity during the aging of the Cannabis sativa plants. The average stem height was 67.5 cm, and the stem diameter was 0.41 cm. The different K sources did not significantly influence the stem height and diameter, nor the dry stem (on average 12.2 t ha&minus:1) and seed yield (on average 1.85 t ha&minus:1). The tensile strength of individual hemp stems was the highest with K2SO4 (53.32 MPa) and the lowest with KCl (49.25 MPa). The stem stiffness by modulus of elasticity was about 5 GPa on average for all the treatments. In general, the photosynthetic parameters in this study varied more between the growth stages than between the different K fertilizer formulations. Moreover, based on the results of this study, it can be recommended to use both fertilizers, KCl and K2SO4, in dual-purpose industrial hemp production since no significant effect was found for the stem morphometric and biomechanical parameters as well as for the agronomic parameters.