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Large parts of New Zealand have been in agricultural production for less than one hundred years. In many cases farmers are still trying to develop their properties. The ability to top-dress fertilizer from aircraft has been an important part of that development as access is impossible with wheeled vehicles and because of the large areas that need to be covered. Recognition of the variability of the pastoral country gives an opportunity to further target development expenditure. Poor economic utilization of fertilizer usually means greater opportunity for nutrient leakage and adverse environmental impacts. Further developments in VRAT cause us to examine the levels of precision in existing systems and their effect on economics of operation. A method of system analysis is presented both in terms of the basic ability of blanket application systems, followed by the impacts of implementing variable rate. The flowability of material from the aircraft is an important factor in determining the uniformity of spread. Further studies are being performed to achieve a better understanding of the environment within the aircraft and the properties of the material being spread that affect the spread characteristics. Environmental agencies are also placing restrictions on the physical and chemical properties of material that can be spread from an aircraft as a permitted activity. Much more emphasis is placed on proof of placement and in a number of quality assurance programs it is a requirement.