Over recent years, some hopyards of northeast Portugal have presented poorly developed
plants and reduced productivity. In this study, an attempt was made to improve the homogeneity
of hop fields and restore their productivity by using plant biostimulants as foliar sprays. The
experimental apparatus included four field trials carried out in four plots of different plant vigour, as
evaluated by farmers over previous years (weak, fair, good and very good). The experiments were
arranged as a factorial of foliar treatment (two plant biostimulants containing extracts of seaweed
algae and an untreated control) and year (2017 and 2018). The plot and the year influenced greatly
almost all the measured variables related to tissue nutrient concentration and crop performance. In
the control plots, cone dry matter (DM) yield varied from 83.3 to 394.4 g plant1 from the weak to
the very good plots. In 2018, cone DM yield was significantly higher than in 2017. The use of foliar
sprays influenced less the elemental composition of plant tissue than the plot or the year. The use
of foliar sprays only increased significantly crop yield in the plot of weak plant vigour. The foliar
treatments did not increase - and -acid concentration in the cones; in the control treatment of the
most productive plot, the values were, respectively, 11.2 and 3.9%. Although seaweed extracts tend
to help plants cope with several abiotic and biotic stresses, they showed to be effective in mitigating
the stress that is affecting these plants, which probably is poor soil drainage caused by the flooding
irrigation system, only under conditions of severe stress.
The authors are grateful to the Foundation for Science and Technology (FCT, Portugal)
for financial support from national funds FCT/MCTES, to CIMO (UIDB/AGR/00690/2020) and for
Sandra Afonso’s doctoral scholarship (BD/116593/2016).
