Maintenance dose
If a farmer goes to the trouble of having soil samples analysed (normally by his fertilizer supplier) and there is enough N and P, the farmer will be told to apply a maintenance dose. That is a relatively low level of fertilizer, most of which gets washed away into the local water courses without affecting the crop. The fertilizer company REALLY does not want the farmer to not use their product - They might stop buying it when they don't need it...
Biting the hand that feeds IT
