Equivalent Fluid Pressures of bulk fertilizer / salt

I am a structural engineer needing to design some retaining walls for a building which is going to have bulk fertilizer stored against it. This would be similar to a salt storage building. My walls are going to be vertical and I'm interested in knowing how to determine an effective fluid pressure acting on the wall of bulk fertilizers (range is fine since I'm sure different fertilizers have different densities, angles of internal friction, etc). I'm also interested in how salt would act pressure-wise on a vertical wall surface.

Thanks.

Alan ■