Best approach is to try a foliar spray on a limited area or a surface application in a strip first, at these low rates. Observe and follow up. My own experience has shown that for very limited areas, products such as Miracle Grow and liquid formulations of chelated iron work very well. I have used them in the greenhouse and garden, with very good success. Follow the label exactly, especially as foliar sprays, since they have very high salt concentrations and can be very injurious to plant tissue.
Foliar sprays are the principal means of applying iron to crops, such as for fruit trees.
Severe iron deficiency may require switching from a sensitive crop to more tolerant crop. Rates of application for soil treatments vary from as little as five pounds of Reax Iron, or one gallon of THIS Iron to as much as 1,000 pounds of ferrous sulfate per acre. As a foliar spray, as little as 0.5 percent Reax Iron, THIS Iron, or ferrous sulfate solutions may be applied as foliar sprays on sensitive crops. Some organic or chelated forms of iron applied to deficient soils are generally very effective, while most inorganic salts are not effective under calcareous conditions. Instructions for each product should be followed closely.