You have a really good base here. When looking for realism there are 2 things that stand out. Solid flat saturated colors tend to look cartoonish. With realism, you will have more of an unsaturated(or greyed out) base, especially in morning light. And then the other is texture. To get more realistic, you need to bring in texture. This usually means contrast. For the background, it just needed a bit of that contrast with some bright sunlight hitting areas. As you come closer, that light becomes more saturated and the contrast becomes more evident. A bit darker darks in the shadows and brighter brights in the sunlit areas. Then adding in the texture to that large flat green grass area. Hope this helps.

