This recommendation is specific to Texas and may or may not apply to your area.
The common reason for the lumpy, bumpy appearance, or the sand dune effect, that you describe is not the unevenness of the soil but the mowing of the grass. I suspect that you are mowing your Emerald zoysia with a rotary-type lawn mower and are not mowing it frequently enough. Emerald has extremely wire-like blades and, if mowed with a rotary mower (especially one that is not very sharp), many of those blades will just be pushed over instead of cut. This eventually causes the lumps. Then, when you lower your mowing height to try to correct this, you cut the top off the lumps, leaving brown spots. Emerald is best mowed with a reel-type mower and should be mowed frequently at a height of 1 to 2 inches.
