Soil and nutrition
Chlorosis: iron chlorosis in orchards, vineyards and cotton
On calcareous, alkaline soils iron is present but plants cannot take it up. Young leaves turn yellow between the veins while the veins stay green, and photosynthesis falls. Yield and quality suffer, most of all in fruit trees and vineyards.
Crops: Orchards, Grapes, Olive, Soybean, Maize, Cotton
When it is dangerous
The most sensitive phase is active growth: iron does not move inside the plant, so every new leaf is at risk – in orchards, the spring flush. At budding and flowering weak photosynthesis hurts yield formation, and during fruit fill it hurts fruit quality. Under irrigation the risk rises when calcareous soil is waterlogged or the water carries bicarbonate.
Causes
- Calcareous soil with alkaline reaction – pH above 7.5
- High active lime in the soil: the risk grows above 10%
- Bicarbonate in irrigation water
- Waterlogging on calcareous soil
- Low available iron in the soil
Signs on the field
- Yellow or almost white tissue between green veins on young upper leaves
- In severe cases, young leaves bleach and die
- Short internodes in fruit trees
- Pale patches in the canopy on part of the field
How ClusterOS notices it
In Sentinel-2 images ClusterOS sees that part of a field has turned paler and lost leaf area. But a 10 m satellite cannot tell iron chlorosis from nitrogen shortage: both cause the same drop in chlorophyll, and imagery shows it late. The key sign – a yellow net between green veins on young leaves – is visible only to an agronomist in the field or a drone. So the image shows where to look, and the diagnosis comes from a field check and a soil test.
What to do
- Inspect the pale areas: yellow young leaves with green veins point to iron, evenly yellow old leaves point rather to nitrogen
- Test the soil for pH, carbonates and active iron – total iron in leaves is misleading
- Check irrigation water for bicarbonate and change the source if needed
- Apply iron chelates and avoid waterlogging calcareous soil; a response to chelates confirms the diagnosis
Questions
How do I tell iron chlorosis from nitrogen deficiency?
Look at which leaves turn yellow and how. With iron shortage the young upper leaves yellow while the veins stay green. With nitrogen shortage the older lower leaves yellow evenly.
Why does a leaf test show normal iron when the leaves are yellow?
This is the known chlorosis paradox: a yellow leaf can hold as much iron as a green one. The problem is not the amount but that the plant cannot use it. Diagnose by soil pH, carbonates and active iron instead.
Learn about this risk on your fields before it becomes a loss
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Other risks in «Soil and nutrition»
Scientific basis
- Обзор известкового хлороза, Nutrient Cycling in Agroecosystems, DOI: 10.1007/BF01049769
- Morales F. et al., работы по парадоксу хлороза
- Korcak R.F. 1987
- Marschner's Mineral Nutrition of Higher Plants, 3-е изд., 2012