Effects of the Annual Nitrogen Fertilization Rate on Vine Performance and Grape Quality for Winemaking: Insights from a Meta-Analysis

Sustainability in grapevine cultivation requires the precise use of water and fertilizers, particularly nitrogen (N), to produce grapes of the highest quality for winemaking, while simultaneously avoiding harm to the surrounding waters and atmosphere by reducing NO3− losses and N2O and NH3 emissions from the vineyards. To address the challenge of optimizing N use in viticulture, many N fertilization trials have been carried out over the last decades, and a compilation and analysis of worldwide trials was therefore needed. The present study tackled this challenge through a meta-analysis of published research, which included 374 fertilization trials. From the compiled data, six vine production parameters and eight grape quality traits were extracted and normalized to enable comparisons between experiments. The Mitscherlich law of diminishing returns was able to satisfactorily describe the set of vine production parameters against nitrogen application rate, and the same occurred with the yeast assimilable nitrogen (YAN). In vines, both reproductive and vegetative growth similarly responded to the N application rate. In general, the nitrogen requirements for 95% of the maximum grape yield amounted to rates between 30 and 40 kg·N·ha−1, which increased nitrogen use efficiency (NUE) to values between 0.27 and 0.36 t·kg·N−1. Although several grape quality traits could not be described against the N rate in terms of any mathematical relationship, an N rate between 20 and 25 kg·N·ha−1 could be considered as maximizing grape quality for winemaking. Such N fertilization range increases NUE up to values between 0.41 and 0.47 t·kg·N−1, thus almost doubling the known NUE standards when grape quality is targeted instead of yield, although soil fertility could be exhausted in the mid-to-long term. Whatever the case, anthocyanins and polyphenols are well preserved in red grapes at such low N rates, although YAN is not. The results of this work will be useful for guiding new vine N nutrition research and N nutrition management in vineyards, thus increasing wine growing sustainability.