Plutonium is an alternative; thorium as fertile material.
View page
Uranium-238 is a fertile nuclear material that is useful in
producing fissile material (Plutonium 239)
View page
Flood plains are formed when the river overflows its banks.It
deposits layers of fine soil and other material collect sediments
which are very fertile.
View page
No, it is purely mineral with no organic material that would be
needed by plants.