Foliar Fertilisation in Viticulture: Comparison of Two Mineral Fertilisers

Verdenal T., Dienes-Nagy Á., Belcher S., Reynard J.-S., Zufferey V.

Original article appeared in Swiss Agricultural Research

15.04.25

Photo: Agroscope,
Carole Parodi

Foliar fertilisation around veraison improves grape nitrogen levels without affecting vigour. A trial shows that the fertilisers ‘Safe N 300’ and ‘Folur’ effectively increase assimilable nitrogen in the grape must; however, their degree of effectiveness depends on climatic conditions.

Foliar fertilisation is an essential practice in agriculture – particularly in viticulture – for optimising rapid nutrient assimilation and preventing grape nitrogen deficiencies. Unlike root uptake, foliar uptake is passive and dependent upon the leaf-surface nutrient concentration gradient. Applying foliar nitrogen in the form of urea around veraison (BBCH 81 stage) increases grape nitrogen levels, thereby preventing stuck alcoholic fermentation and organoleptic deviations during winemaking. Vine vigour was not affected.

A trial was conducted from 2017 to 2019 on a Chasselas plot in Pully, Switzerland to test the efficacy of two mineral foliar fertilisers compared to a non-fertilised control (Table 1). The fertilisers were applied in two treatments of 5 kg N/ha around veraison with no additional fertilisation. The measured parameters included vine vigour, yield, grape quality and levels of assimilable nitrogen in the musts.

Variant	Supplier	Nitrogen Concentration	Forms of Nitrogen	Amount Applied
Control 0	–	–	–	–
Folur	Tradecorp, Madrid	20% p/p	urea	2×5 kg N/ha
Safe N 300	Yara, Paris	26% p/p	4% ammonium 4% nitrate 12% urea 6% urea formaldehyde	2×5 kg N/ha

Table 1. Trial variants. Each variant contains 15 vines and was repeated four times in randomised homogeneous blocks. Fertilisers were applied to all of the foliage on two occasions around veraison. Chasselas, Pully, 2017-2019.

Both tested fertilisers shown to be effective

The results show that the climatic conditions of the vintages strongly influenced grape nitrogen levels. The hot, dry 2018 vintage (385 mm precipitation, average temperature of 18.6° C during the April-September growing season), favoured better fruit ripening but limited the accumulation of assimilable nitrogen in the must (89 mg N/L in the non-fertilised control). Conversely, the cooler, more humid 2017 and 2019 vintages led to better plant nitrogen assimilation (average 132 mg N/L in the must) (Figure 1).

Foliar nitrogen application significantly increased the level of assimilable nitrogen in the musts. The two fertilisers tested demonstrated a similar efficacy without affecting yield or grape maturity. Increases in assimilable nitrogen varied according to the year: an average gain of 62mg N/L in 2019 as compared to just 24mg N/L in 2017 and 2018. In 2018, despite fertilisation, nitrogen levels failed to reach the critical threshold of 140mg N/L, jeopardising a potential improvement in wine quality. By contrast, in 2017 and 2019 this threshold was exceeded thanks to fertilisation, ensuring a good nitrogen balance.

‘Safe N 300’ marginally outperformed ‘Folur’, although the differences between the two over the whole of the three-year period were negligible. The use of several forms of assimilable nitrogen seems to have contributed to greater fertilisation efficacy.

Figure 1. Assimilable nitrogen (amino acids + ammonium) in the must at harvest, according to year and foliar fertilisation. Chasselas, Pully, Switzerland. The error bars represent the standard deviations; the values accompanied by different letters are significantly different according to the Tukey test (p < 0.05).

Conclusions

Foliar fertilisation around veraison is an effective solution for limiting nitrogen deficiencies in the musts, when used in conjunction with other agronomic strategies that aim to optimise grapevine nitrogen nutrition.
The climatic conditions of the vintage play a major role in the assimilable nitrogen content of the grapes.
Foliar nitrogen application at the veraison stage is an effective means of correcting assimilable nitrogen levels in the grapes without affecting vine vigour.
The ‘Safe N 300’ and ‘Folur’ fertilisers effectively increased the assimilable nitrogen content in the musts at harvest and can be recommended at a level of 10-20kg N/ha for foliar fertilisation of the vine at the veraison stage.
Where the concentration of assimilable nitrogen in the grapes is extremely low, foliar fertilisation may be insufficient to reestablish levels above 140 mg N/L, the threshold for acute deficiency during white-wine vinification.