Iron is necessary for maintenance of chlorophyll in plants. It also plays important role in the formation and activity of series of respiratory enzymes. Iron is relatively immovable in plants and tends to remain in order leaves, because of this newly formed leaves remain greenish in colour. If soil Ph is low the availability of ferrous is more if soil Ph is high availability if iron is very less so ferrous deficiency is high in high Ph soil.
For all crops, especially growing in black soil requires more ferrous, paddy, sugarcane, groundnut, wheat maize, turmeric & cirtus are the major crops growing in black soil requires more ferrous.