A pretty popular thing this effect is. Requires knowledge of basic photoshop.

Create a new layer having 1024x768 px and 72 dpi. Select now the Rectangle Tool (U) to represent the background for the picture to be next.



Blending Options-Gradient Overlay



Gradient’s parameters:



The new layer must be painted in white color by using the Paint Bucket Tool (G). Click after that on the next option on this layer:



Press three times on Ctrl+F. Press on the Add a Mask on the layers, Fill 50%, Blending Mode - Soft Light. The Gradient Tool will be helpful to dark out the lowest part of the picture.



Choose the Brush Tool (B) and represent the grass on a new layer (press the right button on the picture and select)

Select two colors for the brush: CCDC4A and 7FB51B from the left panel, the way it is demonstrated in the next picture. Applying smooth motions, we have to represent the hills covered with the grass.