Split toning is almost the same as color grading. Split toning was an older tool on Lightroom that allowed you to adjust the colors, and shadows of a photograph, and alter the mood of a photo. Color grading can do all of that plus more. You can use the color wheels to make more specific changes to your photo. Also, there are more sliders that allow you to blend the colors and add shadows to the image. It is much more than the sliders that were offered by split toning.