Does foliar fertilization with Seaweed improve the productivity and quality of ‘Merlot’ grape must?

Developing technologies that help vines survive and produce in quantity and quality within current times is mandatory. In this sense, in the 2021/2022 agricultural harvest, the influence of the foliar application of seaweed – Laminaria japonica was studied, aiming at productivity and quality of the must in the 'Merlot' grape. In the city of "Santana do Livramento", "Rio Grande do Sul" (RS), Brazil; in a 15-year-old commercial vineyard of 'Merlot' clone ENTAV-INRA® 347, grafted onto 'SO4' rootstock, the following treatments were applied on 6 occasions: No treatment (control) and; Foliar application of Laminaria japonica seaweed (commercial product: Exal (ALAS), 2 kg ha-1) The treatments consisted of 4 replications (interval) and each interval had 4 plants. The response variables evaluated at harvest time were: productivity (t ha-1). Using the WineScanTM SO2 equipment (FOSS®, Denmark) the must was evaluated: density [g (cm3)-1], sugars (g L-1), pH, tartaric acid (g L-1), malic acid (g L-1), gluconic acid (g L-1), ammonia content (mg L-1), potassium content (mg L-1), total acidity (g L-1 in tartaric acid). The treatment with foliar application of seaweed stood out in productivity (11.3 t ha-1) when compared to the control treatment (9.8 t ha-1). In the must, the potassium content showed significant differences between the treatments, with a reduced level being obtained with the foliar application of seaweed. It is preliminarily concluded that the application of foliar fertilizer based on seaweed (Laminaria japonica) increased the productivity of 'Merlot' vines and reduced the potassium content in the must. Acknowledgements: To the Company "Algas" América Latina Agricultura Sustentável (ALAS), in the names of its managing partners, Luis Augusto Bennemann de Souza and Fernando Carbonari Collares, for the donation of organic fertilizer composed of Marine Algae (Exal), and for the contribution with some inputs to the execution of this research.