# Why do we say that in non-relativistic limit we need only two component spinor?

Why do we say that in non-relativistic limit we need only two component spinor? (As in Schrödinger equation, we do not even talk of spinors,... they are one component object) I have read this statement in several books discussing non relativistic limit of Dirac equation.

The term "Schrodinger equation" is ambiguous, and can sometimes refer to the abstract equation $H|\psi> = E|\psi>$ and sometimes refer to more specific things such as the spacial portion of the non-relativistic wave-function. The non-relativistic wave-function of a particle with spin does involve spinors, so the general Schrodinger equation applied to it has both a spacial part and a spin part.
It's true that the spinors you need to describe a non-relativistic particle are only 2-component rather than 4-component, as long as the particle's kinetic energy is much less than its rest energy ($\frac{p^2}{2m} << mc^2$)