Nitrogen isotope ratio (δ15N) as a tool to trace the major nitrogen source in vineyards

Aim: to elucidate if it is possible to detect variations in the source of nitrogen (organic vs. inorganic) measuring nitrogen isotope ratio (δ¹⁵N) in berries and to examine the degree of variation occurring for this parameter naturally within a vineyard.

Methods and Results: two nitrogen fertilization strategies based on the use of organic and inorganic nitrogen sources were compared through four consecutive seasons in a vineyard, and berry δ¹⁵N was measured at harvest. The source of nitrogen affected remarkably nitrogen isotope ratio, as samples from organically fertilized vines always showed higher δ¹⁵N values. Additionally, variations in berry δ¹⁵N were measured during two seasons in a 60-node sampling grid in a 4.2 ha vineyard, showing that a wide range of variation existed for δ¹⁵N within the vineyard, and that its values followed a structured pattern that was in accordance with variations in altitude, being lower in the highest parts of the field.

Conclusions:

The source of nitrogen (organic vs. inorganic) affects berry δ¹⁵N. Nevertheless, the degree of variation observed naturally within a single field is very relevant, and associated to variations in altitude. 

Significance and Impact of the Study: this is the first study that, to our knowledge, demonstrates a direct relationship between nitrogen source and nitrogen isotope ratio in grapevines, and opens the door to its use in grapevine nutrition and terroir studies.