THe techiques I used here are a little advanced. First I decided that row of hay-stacks in the middle are the main point of interest. To obtain the right balance I could crop the top; thus moving the line of hay off the center ( a good thing). Or I could crop the grass and move the hay down. I decided to crop the grass because the sky is more interesting the field.

- I think created a layer from the image
- Created a layer mask using "select color"
- Turned the layer mask into a clipping mask
- Adjusted the levels of the mask.

This allowed me to darken the sky without darkening the ground.

Hope you like the effect.
Charlie