Step 4

On each of the ground layers, make a new layer, change the mode to Overlay 100% and fill it with 50% gray.

Activate the Dodge Tool (O with Midtones Range, Exposure about 20-25% to brighten the details on the contour of the ground parts to fit the light on the background (we'll add it in the next steps). You can see how I did it with Normal mode and the result with Overlay mode.

Step 5

Select the ground layers and the dodge ones and hit Ctrl+G to make a group for them.  Change the group mode to Normal 100% and on top of the layers within this group, go to Layer > New Adjustment Layer > Curves  and decrease the lightness. On this layer mask, use a soft black brush to erase the dark effect on the right of the background and midground to reveal the lightness there.