Nutrients and limiting factors

The terms 'nutrient' and 'limiting factor' summarise the results of an experiment in which increase in supply results in an increased response. By extension they are often - perhaps usually - used when the user believes that were such an experiment made it would have this characteristic. If the supply is further increased the response diminishes and may, eventually, become negative. 'Nutrient' and 'limiting factor' therefore apply, strictly, only when the circumstances are specified: they cannot be attached to a particular substance without qualification. The claim that 'nitrogen is a nutrient (or limiting factor)' is incomplete. All nutrients are limiting factors, but the reverse is not true. The widespread belief that only one factor can limit a complex process at one time is demonstrably false in general, though it may sometimes be true in particular cases.