Evaluation of the impact of different nitrogen fertilisation forms and techniques on yeast-assimilable nitrogen (YAN) in <i>Vitis vinifera</i> L. cv. Riesling: A three-year field study

Efficient nitrogen fertilisation in viticulture has the dual challenge of enhancing grape quality while reducing the environmental impacts associated with nitrogen use. This three-year field study evaluated different nitrogen fertilisation forms and application methods for the perennial fruit crops Vitis vinifera L. cv. Riesling, including foliar, topsoil, and subsoil applications at a rate of 50 kg N ha ⁻¹. The study focused on the impact of nitrogen fertilisation on nitrogen content, nitrogen use efficiency and amino acid concentrations in grape berries and must. Results show that foliar fertilisation with urea is particularly effective, improving nitrogen levels in berries, nitrogen use efficiency (NUE), and amino acid composition as well as overall yeast assimilable nitrogen (YAN) in all three test years. N fertilisation by fertigation enhanced N levels in the berries and leaves as well as overall YAN and amino acid composition in two of the study years but to a lesser extent than foliar fertilisation with urea. Fertilisation with controlled uptake long-term nutrition process positively affected berry N, amino acid composition and total YAN in one year. While N fertilisation with ENTEC® increased N concentration in the berries in one year, no other effects were observed. No effects on berry N, YAN or amino acid composition were observed when grapevines were fertilised with calcium ammonium nitrate, but an increase in soil nitrate was observed after the season in November 2013. Fertilisation with compost did not result in any improvement of the tested parameters and NUE compared to the unfertilised control was negative in all 3 years. Foliar fertilisation with urea demonstrates a notable potential for maintaining adequate yeast-assimilable nitrogen (YAN) - essential for healthy fermentation - in grape must, even under dry conditions. This potential is increasingly prevalent under projected climate scenarios of increased water limitation. Findings suggest that foliar urea application can support fermentation quality in winemaking while offering a sustainable nitrogen management strategy adaptable to varying viticultural conditions.