The coffee plant's roots breath and actually need some air. Thus, constant watering of the coffee plant, or the coffee plant sitting in water, causes the leaves to turn yellow, young shoots wilt, and the coffee tree dies. The coffee plant likes high humidity of about 90 percent. The humidity in the air performs two functions for the coffee plant, one is to keep evaporation from the coffee plant at a minimum, the other is to diffuse the light striking the coffee plant. Coffee plants like filtered to moderate sun light.
Coffee grows on sides of mountains which makes for natural partial lighting conditions.
However, some types of coffee plants can take direct sun light without overhead shade trees or a mountain side cutting off a half days light. And again, this differs with coffee plant types. Bare soil loses its richness and character by being baked by the sun and beat on by the rain. If the sun bakes the top soil too much, the coffee plant's roots die. Therefore, for most coffee plants, the soil should be shaded as much as possible.