Thanks for the comments.
arisdemos - I used one simple cloud layer for the clouds, and I increased the glow power in the lighting settings of the atmosphere to get the brightness to the left.
Calico - I agree that using a blendshader has its benefits, but I frankly feel that the patchiness of grass is often overdone. When I'm walking around in the prairie that's fairly close to my home, I rarely see any kind of clumping. When looking at renders that feature large grass expanses, it's actually the ones with the soft, noisy patterns that look the nicest to me and seem to have the most realism. Not to say that patchy grass doesn't have its place (it works really well in your image); I just don't feel like it fits into what I was trying to accomplish here very well.
