It should be continually recycled Steve, in an ideal world anyway.
In a nutshell it's when fertiliser is used to excess that's where the problem lies. If we use 'just enough' fertiliser then the plants take it in, we eat the plants and there are very low levels left in the soil, so we top the levels up next year or whatever. The problem is/has been that farmers put phosphate into the soil, when the soil already has more than enough phosphate present. The excess ends up in the groundwater or as run off etc. This is quite simplistic and part of the bigger picture, but that's what's been happening in the UK for years. Govt has passed legislation to keep levels down, the EA has recently employed people to measure the levels present. Crazy really, farmers using more than they need is costing them £££s and ballsing up the environment. You'd think they would have twigged sooner?
