Rates for maintenance requirements depend on the original fertility of the soil and its ability to retain applied phosphate in a form which is not readily available to plants. The correct rates depend on the amount of growth of the pasture which, together with management factors and type of farming practised, determine the losses of phosphorus through transfer of fertility and through stock and stock produce sold off the farm. Very little experimental work has been done on maintenance requirements, but it appears that these may vary from 1 cwt superphosphate per acre every few years on the more fertile soils of the South Island to 3–4 cwt per acre each year on some of the “high phosphate fixing” volcanic soils of the North Island.