Yes, different kinds of vegetational covers can be identified. Agricultural land is much more organized than nonurbanized, non- farming land. Band 4 is the easist to use to see vegetation. Band 4 has the highest reflectance. Band 3 has the lowest reflectance.
Spectral reflectance is the amount of light reflected from the land.
For me, the features are easier to see using one band. I think that the single band images are easier to interpret. Advantages to combining bands are that the features have greater contrast, and that certain features have higher reflectance. Disadvantages to combining bands are that the features are not as easy to identify and are not as clear, the image is not really like a picture but an x-ray.