Benchmarking the relationship between nitrogenous compounds in wine grape juice with nitrogen fertiliser applications to determine nitrogen fertiliser replacement value

To accurately use organically derived nitrogen (N) sources to meet plant N demand it is useful to know their equivalence to mineral N fertilisers, which are the industry standard.
This equivalence is frequently calculated for annual plants in arable systems but has not yet been attempted in Vitis vinifera (grape vines). This study tested five yield and juice attributes which hold potential as indicators of N fertiliser rate in vines: yield, yeast assimable N (YAN), YAN_total (YAN multiplied by yield and a juice extraction factor), apparent nutrient efficiency (ANE) and apparent nutrient recovery of the fruit (ANR_fruit). Eight levels of fertiliser 0, 8, 16, 24, 32, 40, 48 and 56 kg ha^‑1 were applied to vines for three years on two sites of contrasting soil type.
YAN was found to have a linear correlation with N fertiliser rate with r² values of 0.4-0.7 and thus was the best indicator of mineral N equivalence.
Yield was decoupled from N fertiliser rate and was therefore a poor indicator.
ANE and ANR_fruit were unreliable indicators, being sometimes very closely correlated to N fertiliser rate (r²>0.9) and other times not significantly correlated at all.
The use of yield in ANE and ANR_fruit calculations is understood to be the source of this unreliability.
The relationship between YAN and N fertiliser rate increased over successive years of treatment, highlighting the value of multi-year trials when establishing NFRV in perennial crops such as wine grapes.

II International Symposium on Precision Management of Orchards and Vineyards

P. French, M. Hardie, N.D. Swarts

Vitis vinifera, organic nitrogen fertiliser, yeast assimable nitrogen, perennial horticulture

https://doi.org/10.17660/ActaHortic.2024.1395.22