WINETECH Technical Yearbook 2019

ASTRID BUICA, ALÉTA BRUWER & WESSEL DU TOIT: Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch KEYWORDS: Foliar fertilisation, sulphur, nitrogen, YAN, amino acids, glutathione. SEPTEMBER 2019 NITROGEN AND SULPHUR FOLIAR FERTILISATION (PART 2)

In this three part series, we explore some fundamental aspects of sulphur and nitrogen foliar fertilisation and the chemical and sensory results of a recent project that took place in South Africa. Part 2 of the series focuses on the effects of the nitrogen and sulphur foliar fertilisation on the non-volatile composition of grapes and musts. INTRODUCTION All recent international studies of foliar fertilisation looked only at selected aspects related mainly to the chemical composition of the grapes and wines. Driven by renewed interest, more research on foliar fertilisation was reported in the past years. The research study presented here was done in South Africa over three seasons and took a more comprehensive approach (Bruwer, 2018). We looked into some specific aspects, but also into the overall effect (combination

of individual effects) of the treatments. Since a vineyard treatment will affect not only the composition of the grape, but will have a lasting effect all the way to the wine, evaluations took place throughout this process. EXPERIMENTAL LAYOUT AND TREATMENTS A checkered design was used in the field experiments. The general layout in a vineyard row followed a pattern of 12 experimental vines, three buffer vines, followed by the next 12 experimental vines. Treatments never started next to a road (at the end of a row). The layout was also adapted to the vineyard block itself, and looked like the layout presented in Figure 1. Due to circumstances beyond our control, three different vineyards were used for Chenin blanc and two for Sauvignon blanc throughout the three years of the project.

In addition to a control (C) that received no foliar fertilisation, three different treatments were applied to the experimental vineyards. The treatments consisted of nitrogen (N, Ureum LB), sulphur (S, Microthiol), and nitrogen+sulphur (N+S) equivalent of 10 kg/ha N and 5 kg/ha S. The calculation was done taking into account the number of vines per ha and the number of vines treated. In our case, we used 1.176 g N/vine

and 0.588 g S/vine, translating into 25.56 g Ureum LB product and 7.35 g Microthiol product per 12 vine treatment, dissolved in 20 L water. Two foliar sprays were applied to each vineyard every season. Foliar fertiliser sprays were applied first approximately two to three weeks, and second, one week before véraison. There were at least 10 days between the treatments.