Iron deficiency in tomato is characterized by an intense chlorosis (yellowing) at the base of young leaves, with the midrib and leaf veins remaining green. These symptoms are called interveinal chlorosis and netting respectively. At later stages, the chlorosis extends to the whole leaf and leaves gradually take a bleached aspect. Brown necrotic spots appear on the highly chlorotic lamina. At this stage, the application of foliar fertilizers containing iron can still rescue the leaves and the plants. Veins are the first to recover, showing a bright green color. The re-greening of the veins after the application of iron is the most recognizable symptom of this disorder.
Iron deficiency can be a serious problem in calcareous, alkaline soils or in poorly drained soils that flood easily and create anaerobic conditions in the roots. The absorption of iron by the plant and the yield response seem to be directly related to the concentration of CaCO3 in the soil and its pH. Another factor limiting the availability of iron to the plant is excess of heavy metals in the soil. Because iron has a low mobility, iron deficiency symptoms appear first on the youngest leaves. Leaf chlorosis and necrosis reduce chlorophyll content, inhibit the photosynthetic rate, retard growth and lower the yield potential of the tomato plant. The optimal pH for the growth of tomato plants is 6.5.
Organic matter in animal manures, peat and composts can be used to add iron and other nutrients to the soil. They enhance soil structure, improve the water and nutrient holding capacity and serve as reservoir of nutrients. Nutrient availability can vary widely depending on the type of material used and the environmental conditions.
There are several fertilizers on the market that contain iron.The most common and inexpensive strategy is to correct the iron deficiency while preparing the field at bedding. Iron sulfate (FeSO4) can be used for this purpose. Iron chelates are also available but they are rather expensive. Foliar sprays are effective in re-greening the crops and may help to save the yield if applied at early stages of the deficiency and at regular intervals (10 days to two weeks). Both iron sulphate or iron chelates can be used as a sprays.
Choose tomato varieties that are less susceptible to iron deficiency.,If possible, avoid planting tomatoes in calcareous, alkaline soils.,Improve the drainage of the soils and do not over-water.,Do not lime, since this will increase the pH of the soil.,Modify soil pH to reach optimal growth conditions for tomato.