Profitable Fertilizer Use

I Initial most effective rate to maximize yield when fertilker is first used. 

Most effective rate to maximize yield after 6 to 8 years of applying fertilizer at rate 1. 

The economic optimum rate of fertilizer is the rate that provides maximum profit-maximum addition to profit as a result of fertilizer use. This rate, say P, is determined by imposing the condition for profit maximization 

The magnitude of added profit due to fertilizer use pressed in monetary v3ue per unit of area, for 

---