Delving into the importance of nitrogen & iron
10th March 2026
Nitrogen and iron are essential building blocks of healthy vines and high-quality wines. Ahead of the new season, Fruit & Vine examines their roles and how to manage these key nutrients.
Nitrogen and iron are central components of chlorophyll formation, so directly impact the vine’s ability to generate a healthy, green, canopy with maximum photosynthetic capacity. Deficiency of either nutrient results in chlorosis (yellowing) of leaves, although different parts will be affected due to differences in their mobility (see table).
As Hutchinsons agronomist Will Robinson explains, nutritional requirements vary for individual situations, depending on many factors, from soil type and nutrient status, to vine vigour and yield.
Managing nitrogen
As a perennial crop with a large root system, vines generally do not require additional nitrogen in the same way as other crops. Often, the main challenge on deeper, more fertile soils is managing excess nitrogen, rather than any deficiency, says Will. Excess nitrogen can lead to over-vigorous canopies at greater risk of fungal diseases, such as mildew or botrytis, shade fruit, and delay ripening.
Furthermore, nitrogen offtake in harvested grapes typically varies from just 10–50kg/ha, depending on yield, and in many cases, much will be replenished by nitrogen released naturally from the soil, he says.
“However, we find growers who are consistently achieving high yields (over 10t/ha) do often apply some additional nitrogen, typically around 50kg N/ha in the form of ammonium nitrate. As always though, discuss specific vineyard requirements with your FACTS-qualified advisor.”
Additionally, where vines struggled to grow in the previous season, some growers may apply early season nitrogen at bud burst to help vines reach the top wire and support larger clusters, Will adds. “If shoots are deficient and you’re not getting the top growth, the vine will abort berries because it’s simply not able to support them.”
Soil analysis should be done first, to check poor growth is not due to any other nutrient deficiency or soil issue, he advises.
“Petiole analysis can also be useful, however, may be too late for nitrogen decisions. If you are going to apply nitrogen, it must be as soon as vines wake up in spring. Avoid applying anything near flowering as this can trigger vines to go into a vegetative, rather than reproductive, cycle, reducing fruit set and berry number.”
Ammonium nitrate is generally preferred over urea, as nitrogen is immediately available, he notes.
“If it’s a really warm spring, vines can go from bud burst to flowering quite rapidly, and if you’ve put urea on, which takes a while to be broken down and taken up by plants, it might be getting into the vine too late.” In England, any urea fertiliser applied to soil in spring must incorporate a urease inhibitor to prevent ammonia losses.
Managing iron
Iron deficiency can be a challenge on some soils, particularly more alkaline (over pH7), says Will. In these conditions, iron is converted into insoluble compounds that plants cannot absorb through roots, even if total soil iron content is sufficient. Iron deficiency can also occur when soils are cold or waterlogged.
Rootstocks such as Fercal are better at absorbing iron from high pH soils, and are often grown on such sites. However, hidden variability in underlying soil conditions across vineyards can sometimes lead to isolated issues with iron deficiency in conventional rootstocks, and high levels of copper, manganese or zinc, are also known to lock-up iron, he notes.
“Prevention is better than cure, so where iron deficiency is an issue, apply foliar iron as soon as there’s sufficient leaf area to hit, ideally from the 3–5 leaf stage. Again, avoid doing anything around flowering, as iron can block pollen receptors.”
Will recommends using products in chelate form (such as Metalosate Iron), as the water-soluble molecules mix easily, do not bond with other nutrients, and are more easily absorbed through leaves, allowing faster uptake and correction of any deficiency.
He cites the example of one vineyard, where a vein of chalky soil running through the site was causing serious iron chlorosis in vines planted on the wrong rootstock for that soil. “Petiole analysis in May showed very low iron, but we managed to bring vines back with regular applications of a foliar chelated iron product throughout the season, apart from during flowering.”
Will concludes by adding: “No one nutrient can be considered in isolation. Everything is interlinked, so you need to understand what is optimum for your situation.”
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