Do we need N and P removal when disposal is on land ?
The 3 main nutrients for plant growth are Nitrogen, Phosphorus and Patassium. So if you discharge wastewater plant effluent to soil, yes it will act as a fertilizer for the plants. Obviously, the balance required for fertilization varie from one plant to another. As with any fertilizer you would have to know what you are applying to your crop (N, and P concentration) in order to fertilize as required.
Before doing any application on land, you should check the regulation. In USA there is a regulation for land application. It may also need a permit.