The 5omm would make a good portrait or general purpose lens, especially good in low light because of the wide aperture, but not really much good for macro unless used with extension tubes maybe. Always best to use an actual macro lens where possible, something like the Sigma 105 or the Tamron 90 would be my recommendations.
As for landscapes well yes, you could use the 50mm but it would be very limiting, especially with a cropped sensor. I would more likely be thinking of a focal range between 10mm and 24mm so probably the Sigma 10-20 or any decent standard zoom lens.
So to answer your original question, Ideally there isn't really a single lens that is good for both macro and landscape, they are essentially different ends of the spectrum.