Everywhere in the world, before the intervention of man and fertiliser, soil, vegetation and animal systems evolved naturally to make the most efficient use of the rate of nutrients becoming available from parent materials, assisted by the local climatic conditions. Except during extreme events such as flooding or earthquakes, losses of nutrients to the outside environment were exceedingly small. Animals died and the nutrients they contained were returned to the soil during their decay. Then civilisation came along, and imposed totally new systems, where considerable quantities of nutrients are being removed in produce, and, to maximise production, plant-available forms of nutrients are kept at very high levels in the soil through the use of fertiliser. Unfortunately, at these high levels, nutrients are prone to loss to the atmosphere (in the case of N), and, in the case of all nutrients, in run-off to waterways and in leaching.

source: http://www.groupone.co.nz