Abstract: A mobile trailer for spreading a granular material mixture is disclosed. This trailer comprises at least two containers or bin compartments for containing a respective granular material, a movement-imparting assembly for moving the granular materials and a material mixer and spreader assembly for mixing and spreading the granular materials. Each bin compartment comprises a respective material-exit opening and the material mixer and spreader assembly is positioned near these openings. The movement-imparting assembly comprises a respective movement-imparting device mounted to each bin compartment for moving a respective granular material though a respective opening towards the material mixer and spreader assembly. A controller is linked to the movement-imparting assembly so as to selectively and independently modulate the speed of each movement-imparting device thereby modulating the ratio of each granular material received, mixed and spread by the material mixer and spreader assembly.