Response of Hops to Algae-Based and Nutrient-Rich Foliar Sprays

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 plant −1 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 α- and β-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.