Iron is a trace element used in many fertilisers, but alone it's used mainly on lawns. It helps with moss control, diseases such as fusarium patch and take-all patch which like high ph turf surfaces, as well as helping in worm control.
Its most common use though is as a moss killer. Regular applications every 6-8 weeks in the winter months will help stop any moss invading your lawn. It also has the added benefit of burning off certain weeds if used regularly and helps prevent algae problems.
Caution: Great care must be taken in the application of this product as over-use can damage lawns (although used correctly it is effective in neutral or slightly acidic soils).
Application rate: 35g sq. m base or dressing, or 60g diluted in 10 litres of water to cover 18 sq. m.